Arctic Sea Ice : Forum

Cryosphere => Antarctica => Topic started by: AbruptSLR on May 06, 2013, 02:08:44 AM

Title: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 06, 2013, 02:08:44 AM
I begin by posting the following article from Science (March 2013) by Carolyn Gramling, which indicates the newly identified risk that the Southern Ocean may start releasing CO2 into the atmosphere with increasing global warming, as well as the challenges for Regional Circulation Models, RCMs, to model this behavior:

Warming World Caused Southern Ocean to Exhale
The attached image shows the location of two sediment cores from the Ocean Drilling Program in the Southern Ocean reveal a million-year-long glacial-interglacial cycle of fluctuating ocean productivity and upwelling, correlating to ice-core atmospheric carbon dioxide records. Colors show average sea surface temperatures from January to March from 1978 to 2010.
Credit: S. L. Jaccard et al., Science (2013)
No land intersects the 60° circle of latitude south of Earth's equator. Instead, that parallel marks the northern limit of the Southern Ocean surrounding Antarctica. At this latitude, swift, prevailing westerly winds continually churn the waters as they circumnavigate the continent, earning the region the nickname "the screaming '60s".
But the Southern Ocean plays a more benign role in the global carbon budget: Its waters now take up about 50% of the atmospheric carbon dioxide emitted by human activities, thanks in large part to the so-called "biological pump." Phytoplankton, tiny photosynthesizing organisms that bloom in the nutrient-rich waters of the Southern Ocean, suck up carbon dioxide from the atmosphere. When the creatures die, they sink to the ocean floor, effectively sequestering that carbon for hundreds or even thousands of years. It also helps that carbon dioxide is more soluble in colder waters, and that the churning winds mix the waters at the surface, allowing the gases to penetrate the waters more easily.
There are signs, however, that the ocean's capacity to sequester atmospheric carbon dioxide has been decreasing over the past few decades, says climate scientist Samuel Jaccard of ETH Zurich in Switzerland. For one thing, the carbon doesn't stay sunk. Even as phytoplankton blooms sequester new carbon, the upwelling of deep, subsurface water currents in the region bring old, once-sequestered carbon back to the surface waters, allowing for exchange with the atmosphere. Meanwhile, the ozone hole has strengthened winds in the region, which may be hindering the carbon storage.
For clues to the future, climate scientists look to past glacial-interglacial cycles. Researchers have a record of atmospheric carbon dioxide stretching back millions of years thanks to ice cores from Antarctica, which contain trapped gas bubbles, snapshots of ancient air. But for the other half of the picture—what happened in the oceans during that time—there is only a relatively short record extending back about 20,000 years to the last glacial cycle. Ocean sediment records, which contain evidence of carbon and nutrients, are one way to reconstruct that history.
Previous ocean sediment records suggest that, as the world slipped into the last glacial period, less carbon overall reached the sediments of the Southern Ocean, coinciding with declining atmospheric carbon dioxide. During cold periods, increased sea-ice cover can keep gases trapped in the ocean—and the drier, dustier conditions bring much-needed iron to phytoplankton in the sub-Antarctic portion of the Southern Ocean, feeding blooms that gobble down carbon dioxide from the atmosphere.
What happens when the world moves into a warm, interglacial period isn't certain, but in 2009, a paper published in Science by researchers found that upwelling in the Southern Ocean increased as the last ice age waned, correlated to a rapid rise in atmospheric carbon dioxide.
Now, using two deep cores collected at two Ocean Drilling Program sites in the Southern Ocean, Jaccard and colleagues have reconstructed ocean records of productivity and vertical overturning reaching back a million years, through multiple glacial-interglacial cycles. This rapid increase in carbon dioxide as the world transitions from glacial to interglacial seems to be a pretty regular thing, they've found.
"There was relatively more carbon dioxide emitted from the deep ocean and released to the atmosphere as the climate warmed," Jaccard says. "The Southern Ocean sink was less effective."
As the world transitioned to glacial periods, on the other hand, atmospheric carbon dioxide decreased. This happened in two steps: First, in the Antarctic zone of the Southern Ocean, a reduction in wind-driven upwelling and vertical mixing brought less deep carbon to the surface. Then, about 50,000 years later, atmospheric carbon dioxide decreased again, the team reports online today in Science. This decrease, Jaccard says, is linked to blooms of phytoplankton in the sub-Antarctic Zone, slightly farther north, driven by an influx of iron carried by dusty winds.
The regularity of the glacial-interglacial signal is intriguing, and "it's a valid point to be making," says Robert Toggweiler of the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey. But he questions how to apply it to the future, because modelers have trouble making models sophisticated enough to reproduce such a signal.
It's known that when ice sheets start to melt, cooling the air in that region, the winds over the Southern Ocean strengthen, Toggweiler says. "The question is how does that signal get to the Southern Ocean?" The ozone hole plays a role in the stronger winds, but so does increasing temperature. So far, no one has been successful at taking the cooling in the north and generating winds in the south that produce much of a carbon dioxide response. "In general, models have been spectacularly unsuccessful in replicating this sort of response we're seeing here," he says.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 06, 2013, 02:25:22 AM
For my second post in this thread, I would like to present the following abstract (and two accompanying comparative images from the article), which illustrate the challenges with modeling Antarctic Bottom Water, AABW, behavior; which is critical to projecting future climate change:

Southern Ocean bottom water characteristics in CMIP5 models by Céline Heuzé, Karen J. Heywood, David P. Stevens and Jeff K. Ridley, Geophysical Research Letters (pages 1409–1414), 15 APR 2013 | DOI: 10.1002/grl.50287

"Southern Ocean deep water properties and formation processes in climate models are indicative of their capability to simulate future climate, heat and carbon uptake, and sea level rise. Southern Ocean temperature and density averaged over 1986–2005 from 15 CMIP5 (Coupled Model Intercomparison Project Phase 5) climate models are compared with an observed climatology, focusing on bottom water. Bottom properties are reasonably accurate for half the models. Ten models create dense water on the Antarctic shelf, but it mixes with lighter water and is not exported as bottom water as in reality. Instead, most models create deep water by open ocean deep convection, a process occurring rarely in reality. Models with extensive deep convection are those with strong seasonality in sea ice. Optimum bottom properties occur in models with deep convection in the Weddell and Ross Gyres. Bottom Water formation processes are poorly represented in ocean models and are a key challenge for improving climate predictions."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 06, 2013, 02:35:23 AM
I have posted this article from MIT before, but I believe that it belongs in this thread:

A climate window in the Southern Ocean: An updated circulation model reveals the Southern Ocean as a powerful influence on climate change
Jennifer Chu, MIT News Office
February 19, 2013
The world’s oceans act as a massive conveyor, circulating heat, water and carbon around the planet. This global system plays a key role in climate change, storing and releasing heat throughout the world. To study how this system affects climate, scientists have largely focused on the North Atlantic, a major basin where water sinks, burying carbon and heat deep in the ocean’s interior.

But what goes down must come back up, and it’s been a mystery where, and how, deep waters circulate back to the surface. Filling in this missing piece of the circulation, and developing theories and models that capture it, may help researchers understand and predict the ocean’s role in climate and climate change. 

Recently, scientists have found evidence that the missing piece may lie in the Southern Ocean — the vast ribbon of water encircling Antarctica. The Southern Ocean, according to observations and models, is a site where strong winds blowing along the Antarctic Circumpolar Current dredge waters up from the depths.

“There’s a lot of carbon and heat in the interior ocean,” says John Marshall, the Cecil and Ida Green Professor of Oceanography at MIT. “The Southern Ocean is the window by which the interior of the ocean connects to the atmosphere above.”

Marshall and Kevin Speer, a professor of physical oceanography at Florida State University, have published a paper in Nature Geoscience in which they review past work, examine the Southern Ocean’s influence on climate and draw up a new schematic for ocean circulation.

A revised conveyor

For decades, a “conveyor belt” model, developed by paleoclimatologist Wallace Broecker, has served as a simple cartoon of ocean circulation. The diagram depicts warm water moving northward, plunging deep into the North Atlantic; then coursing south as cold water toward Antarctica; then back north again, where waters rise and warm in the North Pacific.

However, evidence has shown that waters rise to the surface not so much in the North Pacific, but in the Southern Ocean — a distinction that Marshall and Speer illustrate in their updated diagram, where the attached image shows a new schematic emphasizes the role of the Southern Ocean in the world’s ocean circulation. The upper regions of ocean circulation are fed predominantly by broad upwelling across surfaces at mid-depth over the main ocean basins (rising blue-green-yellow arrows). Upwelling to the ocean surface occurs mainly around Antarctica in the Southern Ocean (rising yellow-red arrows) with wind and eddies playing a central role. Image: John Marshall and Kevin Speer

Marshall says winds and eddies along the Southern Ocean drag deep waters — and any buried carbon — to the surface around Antarctica. He and Speer write that the updated diagram “brings the Southern Ocean to the forefront” of the global circulation system, highlighting its role as a powerful climate mediator.

Indeed, Marshall and Speer review evidence that the Southern Ocean may have had a part in thawing the planet out of the last Ice Age. While it’s unclear what caused Earth to warm initially, this warming may have driven surface wind patterns poleward, pulling up deep water and carbon — which would have been released into the atmosphere, further warming the climate.

Shifting winds

In a cooling world, it appears that winds shift slightly closer to the Equator, and are buffeted by the continents. In a warming world, winds shift toward the poles; in the Southern Ocean, unimpeded winds whip up deep waters. The researchers note that two manmade atmospheric trends — ozone depletion and greenhouse gas emissions from fossil fuels — have a large effect on winds over the Southern Ocean: As the ozone hole recovers, greenhouse gases rise and the planet warms, winds over the Southern Ocean are likely to shift, affecting the delicate balance at play. In the future, if the Southern Ocean experiences stronger winds displaced slightly south of their current position, Antarctica’s ice shelves may be more vulnerable to melting — a phenomenon that may also have contributed to the end of the Ice Age. 

“There are huge reservoirs of carbon in the interior of the ocean,” Marshall says. “If the climate changes and makes it easier for that carbon to get into the atmosphere, then there will be an additional warming effect.”

Jorge Sarmiento, a professor of atmospheric and oceanic sciences at Princeton University, says the Southern Ocean has been a difficult area to study. To fully understand the Southern Ocean’s dynamics requires models with high resolution — a significant challenge, given the ocean’s size.

“Because it’s so hard to observe the Southern Ocean, we’re still in the process of learning things,” says Sarmiento, who was not involved with this research. “So I think this is a very nice snapshot of our current understanding, based on models and observations, and it will sort of be a touchstone for future developments in the field.”

Marshall and Speer are now working with a multi-institution team led by MIT’s collaborator, the Woods Hole Oceanographic Institution, to measure how waters upwell in the Southern Ocean. The researchers are studying the flow driven by eddies in the Antarctic Circumpolar Current, and have deployed tracers and deep drifters to measure its effects; temperature, salinity and oxygen content in the water also help tell them how eddies behave, and how quickly or slowly warm water rises to the surface.

“Any perturbation that is made to the atmosphere, whether it’s due to glacial cycles or ozone or greenhouse forcing, can change the balance over the Southern Ocean,” Marshall says. “We have to understand how the Southern Ocean works in the climate system and take that into account.”
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 06, 2013, 04:51:37 AM
The following two posts include a long excerpt from an April 15, 2013 article from Wired magazine about the importance of modeling eddies in the Southern Ocean; and the attached image shows simulations of Southern Ocean circulation at two levels of resolution. The model on the left, which uses a grid with 1-degree resolution, does not resolve ocean eddies, whereas eddies are resolved in the 1/6-degree model on the right. Image: American Meteorological Society:

Scientists Map Swirling Ocean Eddies for Clues to Climate Change
By Natalie Wolchover, Simons Science News

“What happens in the Southern Ocean has a profound impact on what the climate projections are 100 years from now,” said Sarah Gille, an oceanographer at the Scripps Institution of Oceanography in San Diego and, along with Ledwell and others, a principal investigator on the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean, or DIMES campaign. Earth is warming, and variations in climate models affect whether scientists predict an increase of, for example, 2, 4 or 6 degrees Celsius (3.6, 7.2 or 11.8 degrees Fahrenheit) a century from now, Gille said — “enough to actually make a real difference in climate and how much you worry about future climate change.”
At the high end of that range, many coastal and arid regions that are currently home to humans would become uninhabitable, subsumed by sea or desert.
Sea Changes
The Southern Ocean plays an outsize role in containing global warming, swallowing an estimated 10 percent of the heat-trapping carbon dioxide that humans pour into the atmosphere. But the ribbon of water surrounding Antarctica may be absorbing less carbon than it used to, a study in the journal Science suggested in February, possibly because strengthened winds are dredging up more sunken carbon from the seafloor and causing it to saturate the surface waters. Because subtle changes can trigger a feedback loop in fluid dynamics, some researchers think the Southern Ocean could eventually switch from absorbing carbon dioxide to emitting it (as may have occurred in the ancient past), which would further escalate global temperatures
The Southern Ocean has a powerful effect on Earth’s climate because it “provides a connection between the atmosphere and the deep ocean,” said Andrea Burke, a marine chemist doing postdoctoral work at California Institute of Technology who is not involved with DIMES. It circles Antarctica, enabling surface winds to drive it eastward in a continuous loop. The Antarctic Circumpolar Current, as it’s called, has an average or “mean flow,” while buildups of surplus energy erupt into eddies — circular currents tens of miles across that stir the water and, in a feedback process, reinforce the mean flow.
Because cold, dense water is farther below the ocean’s surface toward the equator than near Antarctica, ocean layers of constant density slope upward as one moves north to south across the Southern Ocean. Eddies and the mean flow draw water from the depths to the surface along these southward inclines, then drive it down again as it moves northward — a conveyor belt called an “overturning circulation” that scientists say is the biggest on Earth.
These circulations conspire to make the Southern Ocean a remarkably efficient absorber of greenhouse gases, which are swallowed at the surface and channeled to the seafloor. And as a driver of global ocean currents, the Southern Ocean bolsters the impact of the other oceans on the climate, too.
But because of the complexity of ocean dynamics, climate change effects — strengthening surface winds (also caused by the hole in the ozone layer) and the 0.8 degrees C (1.4 degrees F) rise in average global temperatures since the start of the Industrial Revolution, for example — could drastically alter these circulations decades from now.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 06, 2013, 04:55:19 AM
This is the second half of the long excerpt for the previous post:

“Understanding the feedbacks between the mean flow and the eddies is critical to understanding future climate change,” said Emily Shuckburgh, an applied mathematician at the British Antarctic Survey and a DIMES principal investigator whose research over the past decade has highlighted the complex role played by eddies in ocean dynamics.
Despite their importance in driving large-scale ocean circulations, eddies are not fully represented in climate models like those used by the Intergovernmental Panel on Climate Change (IPCC), Shuckburgh said. Those models are created by solving an interrelated system of equations at every point on a grid representing Earth. The finer the grid, the more geographic features a model can take into account and the more precisely it can predict the flow of materials such as heat and CO2, which directly impact climate. But ocean eddies are too small for even the most powerful supercomputers to resolve in models of the entire planet. Because these unresolved features strongly influence the behavior of larger features, such as the mean flow and the overturning circulation of the ocean, leaving them out of the picture creates large uncertainties in the models.
The working solution is to “parameterize” ocean eddies by incorporating a term into the equations used in coarse-grained climate models that attempts to capture their net effect. For years, this eddy parameter has been estimated based on satellite measurements and scattered temperature records. “We looked at this and said, ‘This is all great, but no one has ever measured the way that eddies flux heat or CO2. How do we know this has any basis in reality?’ ” Gille explained.
Climate science has suffered from a relative lack of studies of the Southern Ocean “because of its remote location and harsh weather,” Burke said. “This makes the results from the DIMES experiment really useful and unique.”
A rare collaboration of oceanographers, chemists and applied mathematicians in the United States and United Kingdom, the DIMES experiment was founded to fill the gaps in knowledge of the Southern Ocean. About twice per year since 2009, crews from each side of the Atlantic have taken turns traveling to the bottom of the planet to conduct experiments and collect data at sea, which will later be assimilated into climate models.
It’s a long way from the math department at Cambridge University where Shuckburgh spent much of her career. “You understand much better the errors in the measurement if you’ve actually seen how it’s done,” she said.
During the first voyage, the scientists released 80 kilograms (176 pounds) of an inert compound called trifluoromethyl sulfur pentafluoride, or CF3SF5, from a sled being dragged behind their ship a mile underwater. The molecules serve as a “tracer,” mapping the influence of eddies as they corkscrew through the ocean. In subsequent voyages — the seventh is currently under way and has its own blog — the crews have tracked the spread of CF3SF5 by collecting thousands of water samples
“We have such amazing sensitivity that we can run the experiment for five years, and we can still see the tracer after it has spread over thousands of miles of ocean,” said Ledwell, who has spent three decades developing the method.
Just like stirring helps disperse milk in coffee, the scientists expect the tracer to spread faster in eddying regions than elsewhere, especially at depths where eddies tend to swirl in place. Throughout the region, the crew released 200 neutrally buoyant floats that can be tracked with acoustics. The floats map the locations and paths of eddies as they drift through the water, and tracer measurements are then compared to this eddy map.
At the ocean surface, Shuckburgh led another float experiment that tested a novel approach to the study of fluid flow. Over the past decade, applied mathematicians led by George Haller, now of ETH Zurich in Switzerland, and others have discovered the mathematics describing rigid barriers that form in fluids called Lagrangian coherent structures. These structures, which are associated with eddies, organize turbulence by repelling fluids from areas known as stable manifolds and shunting them along contours known as unstable manifolds. Shuckburgh used satellite records of the Southern Ocean surface winds to guess the locations of hyperbolic points, where stable and unstable manifolds meet, and released GPS-rigged floats in those spots. “People thought we were mad,” she said.
The floats traced the arms of the hypothesized unstable manifolds almost exactly, lending support to this new conceptual framework for characterizing turbulence.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 06, 2013, 05:07:57 AM
In this post I present the abstract and one image from:

Closure of the meridional overturning circulation through Southern Ocean upwelling
By John Marshall & Kevin Speer
Nature Geoscience, 5,171–180 (2012)doi:10.1038/ngeo1391

"The meridional overturning circulation of the ocean plays a central role in climate and climate variability by storing and transporting heat, fresh water and carbon around the globe. Historically, the focus of research has been on the North Atlantic Basin, a primary site where water sinks from the surface to depth, triggered by loss of heat, and therefore buoyancy, to the atmosphere. A key part of the overturning puzzle, however, is the return path from the interior ocean to the surface through upwelling in the Southern Ocean. This return path is largely driven by winds. It has become clear over the past few years that the importance of Southern Ocean upwelling for our understanding of climate rivals that of North Atlantic downwelling, because it controls the rate at which ocean reservoirs of heat and carbon communicate with the surface."

The attached image Figure 1a shows a schematic diagram of the Upper Cell and Lower Cell of the global MOC emanating from, respectively, northern and southern polar seas.  The zonally averaged oxygen distribution is superimposed, yellows indicating low values and hence older water, and purples indicating high values and hence recently ventilated water. The density surface 27.6 kg m−3 is the rough divide between the two cells (neutral density is plotted). The jagged thin black line indicates roughly the depth of the Mid-Atlantic Ridge and the Scotia Ridge (just downstream of Drake Passage) in the Southern Ocean. Coloured arrows schematically indicate the relative density of water masses: lighter mode and thermocline waters (red), upper deep waters (yellow), deep waters including NADW (green) and bottom waters (blue). Mixing processes associated with topography are indicated by the vertical squiggly arrows.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: Bruce Steele on May 06, 2013, 08:06:24 AM
ASLR,   In very rough numbers , the oceans take up 25% of anthropogenic Co2, the soils and land plants 25% and the atmosphere  the remaining 50%. The" 50% of Co2 emitted by humans" in the Gramling 2013 paper must be 50% of the Co2 that the oceans absorb. This would better match the   "Southern Oceans swallowing an estimated 10% of the Co2 that humans pour into the atmosphere." in the Natalie Wolchover piece.  The North Atlantic and Arctic deep water as well as North Atlantic and North Pacific Intermediate Waters  contribute the other 50% of the ocean carbon  sink. These different sinks can stay away from direct atmospheric contact for periods of 30 to 1000+ years.  Anything that changed the amount of time these waters take between their formation and their upwelling back into atmospheric contact will ,along with water temperature, change their contribution to the carbon cycle.  Biological productivity, length of time in contact with the atmosphere , and nutrients are also parts of the biological pump but those cold, windy places where cold waters sink and the processes that bring the Co2 rich waters back to the surface are places to watch .         
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 06, 2013, 04:47:35 PM
Bruce,

Thanks for the clarifications (I agree with all of your points).  With such a complex topic, this thread can use all the input that it can get; as clearly possible increased upwelling in the Southern Ocean is one of the hotspots to watch.

Best,
ASLR
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 06, 2013, 04:49:57 PM
So far in this thread I have re-posted extracts and summaries from articles about regional and telecommunication projections of Global Circulation (or Coupled) Models, GCMs, and efforts to better match the observed complex behavior in the Southern Ocean (and adjoining areas); all of which have illustrated risks of current IPCC AR5 GCM projections underestimating global threats from such phenomena as: AABW slowing absorption of CO2; increased upwelling of CDW increasing emission of CO2 from the ocean water; incorrect modeling of eddies resulting in incorrect modeling of currents in the Southern Ocean leading to incorrect ocean - ice melting projections; etc.

Now, I would like to re-focus on the risks and challenges for Regional Circulation (or Coupled) Models, RCMs; that can interface dynamically both with larger GCMs and with Local Circulation Models, LCMs, or advective models for ice shelves, glaciers and ice sheets (see discussion in multiple threads in this Antarctic folder) in a manner utilizing multiple grid nesting in land-atmosphere-ocean-ice models that may allow for practical high-resolution atmospheric - ocean modeling of climate dynamics with regard to glacier-scale mass and energy balance, from:  Mölg, T., and G. Kaser (2011), "A new approach to resolving climate-cryosphere relations: Downscaling climate dynamics to glacier-scale mass and energy balance without statistical scale linking", J. Geophys. Res., 116, D16101, doi:10.1029/2011JD015669.
The need for such a "multiple grid nesting" approach (see the first attached images for an example for mountain glaciers) is illustrated by the following examples (and that in coming posts) regarding regional sea ice-ocean-atmosphere-ice interactions:

1) The importance of regional boundary conditions of roughness and dipycnal diffusivity is illustrated by the second attached images from: Seasonal and spatial variations of Southern Ocean diapycnal mixing from Argo profiling floats by  Wu, et al (2011), Nature Geoscience, Volume: 4, Pages: 363–366, doi:10.1038/ngeo1156; shows the horizontal distribution of topographic roughness and diapycnal diffusivity in the Southern Ocean, with panel a showing the topographic roughness and geographic distribution of high-resolution profiles (white dots) obtained from the Argo Iridium floats used in the Southern Ocean and described in this paper. The color scale represents Log10(Roughness) in m2; and panel b showing the horizontal distribution of diapycnal diffusivity, vertically averaged over the depth range 300–1,800 m, on a 6°×5° spatial grid. The color scale represents Log10(K) in m2 s−1.
It is noted that unless such measured regional conditions are modeled correctly the projected local upwelling and local currents that feed the advective ice melting processes will be incorrect.

2) Regional Eddies:The third attached image from: Sea Level Anomalies on 2012/01/01 exploiting 4 altimeters: Jason-2, Jason-1, Envisat and Cryosat-2. Credits Cnes-Ssalto/Duacs-Esa ; shows clearly the observed (by altimeter) size of eddies from the mixing of cold and warm water (resulting in measurable sea elevation differences).  With telecommunication of increasingly warm deep water from the tropics to the Southern Oceans, the correct regional modeling of such eddies is critical to understanding the observed changes to the ACC.

Other important nested modeling considerations will be discussed in subsequent posts.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 07, 2013, 02:32:00 AM
Ever since the increase in circumpolar wind speed (largely due to the formation of an ozone hole over the South Pole) was identified as the driving factor for the increased upwelling in Antarctica (primarily West Antarctica) that significantly accelerated the ice mass loss from Antarctica (primarily West Antarctica); there has been a heated debate as to whether the winds would change again and if so what would be the influence on upwelling and on ice mass loss.  The following abstracts address this matter, and generally indicate that the expected future increase in circumpolar wind speeds due to global warming will induce more upwelling/overturning and consequently more ice mass loss around Antarctica (most significantly in the WAIS):

Meredith, Michael P., Alberto C. Naveira Garabato, Andrew McC. Hogg, Riccardo Farneti, 2012: Sensitivity of the Overturning Circulation in the Southern Ocean to Decadal Changes in Wind Forcing. J. Climate, 25, 99–110.
doi: http://dx.doi.org/10.1175/2011JCLI4204.1 (http://dx.doi.org/10.1175/2011JCLI4204.1)
Abstract
The sensitivity of the overturning circulation in the Southern Ocean to the recent decadal strengthening of the overlying winds is being discussed intensely, with some works attributing an inferred saturation of the Southern Ocean CO2 sink to an intensification of the overturning circulation, while others have argued that this circulation is insensitive to changes in winds. Fundamental to reconciling these diverse views is to understand properly the role of eddies in counteracting the directly wind-forced changes in overturning. Here, the authors use novel theoretical considerations and fine-resolution ocean models to develop a new scaling for the sensitivity of eddy-induced mixing to changes in winds, and they demonstrate that changes in Southern Ocean overturning in response to recent and future changes in wind stress forcing are likely to be substantial, even in the presence of a decadally varying eddy field. This result has significant implications for the ocean’s role in the carbon cycle, and hence global climate.

Munday, David R., Helen L. Johnson, David P. Marshall, 2013: Eddy Saturation of Equilibrated Circumpolar Currents. J. Phys. Oceanogr., 43, 507–532.
doi: http://dx.doi.org/10.1175/JPO-D-12-095.1 (http://dx.doi.org/10.1175/JPO-D-12-095.1)
Abstract
This study uses a sector configuration of an ocean general circulation model to examine the sensitivity of circumpolar transport and meridional overturning to changes in Southern Ocean wind stress and global diapycnal mixing. At eddy-permitting, and finer, resolution, the sensitivity of circumpolar transport to forcing magnitude is drastically reduced. At sufficiently high resolution, there is little or no sensitivity of circumpolar transport to wind stress, even in the limit of no wind. In contrast, the meridional overturning circulation continues to vary with Southern Ocean wind stress, but with reduced sensitivity in the limit of high wind stress. Both the circumpolar transport and meridional overturning continue to vary with diapycnal diffusivity at all model resolutions. The circumpolar transport becomes less sensitive to changes in diapycnal diffusivity at higher resolution, although sensitivity always remains. In contrast, the overturning circulation is more sensitive to change in diapycnal diffusivity when the resolution is high enough to permit mesoscale eddies.

Morrison, Adele K., Andrew McC. Hogg, 2013: On the Relationship between Southern Ocean Overturning and ACC Transport. J. Phys. Oceanogr., 43, 140–148.
doi: http://dx.doi.org/10.1175/JPO-D-12-057.1 (http://dx.doi.org/10.1175/JPO-D-12-057.1)
Abstract
The eddy field in the Southern Ocean offsets the impact of strengthening winds on the meridional overturning circulation and Antarctic Circumpolar Current (ACC) transport. There is widespread belief that the sensitivities of the overturning and ACC transport are dynamically linked, with limitation of the ACC transport response implying limitation of the overturning response. Here, an idealized numerical model is employed to investigate the response of the large-scale circulation in the Southern Ocean to wind stress perturbations at eddy-permitting to eddy-resolving scales. Significant differences are observed between the sensitivities and the resolution dependence of the overturning and ACC transport, indicating that they are controlled by distinct dynamical mechanisms. The modeled overturning is significantly more sensitive to change than the ACC transport, with the possible implication that the Southern Ocean overturning may increase in response to future wind stress changes without measurable changes in the ACC transport. It is hypothesized that the dynamical distinction between the zonal and meridional transport sensitivities is derived from the depth dependence of the extent of cancellation between the Ekman and eddy-induced transports.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 08, 2013, 05:11:42 PM
So far in this thread I have focused on efforts to calibrate both GCMs and RCMs by matching hind castes to observed responses of the Southern Ocean; however, in this post I would like to briefly list some of the challenges that such GCMs and RCMS (preferably ESMs) should not ignore when they publish projections for future responses including:

- They should consider regional methane emissions (see the "Antarctic Methane" thread started by A4R).
- They should consider accelerating regional ice mass loss from ice shelves (including RIS and FRIS) and terrestrial ice, and changes to: SST, sea ice, currents and winds (see all of the threads for periods from 2012 to 2060 in this folder started by me)
-  They should consider the risk of regional collapse of the WAIS, and the resulting changes to ocean currents (see all the threads for the period from 2060 to 2100 from me in this folder, including discussion of new sea passageways)
-  They should evaluate the risk of regional collapse of AABW production (also see the discussion in the, influence of dust (which could increase the albedo of the AIS) from the desertification of South Africa and Australia due to the pole-ward expansion of the atmospheric Hadley Cells.
- RCMs should consider input of correct boundary conditions from the GCMs (preferably from Earth Systems Models, ESMs)
-  They should link dynamically to get input of correct ice mass loss from local circulation models, LCMs, of advective cells melting glaciers, ice shelves and ice sheets
- They should use different radiative forcing scenarios than the IPCC's cited probabilities of occurrences of the Recommended Concentration Pathways, RCPs, for AR5 which are highly misleading and should be corrected before used to interpret any GCM, RCM, or LCM, projections.
- Readers (policy makers) of GCM, RCM and LCM projections should not focus on median projections and they should remember that uncertainties increase with time into the future (meaning more risk).
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 09, 2013, 02:25:54 AM
While (as stated in the previous post) I have presented results from Local Circulation Models, LCMs, in may other threads, I thought that it would be good to post selected images (from a slide show compiled by Bill Lipscomb's team from the US - DOE and Los Alamos National Lab.) regarding recent research using the Community Ice Sheet Model (CISM):

- The first image shows key software in CISM
- The second image shows the concept of using software packages to fight on many challenging fronts at once for both GIS and WAIS types of ocean, atmosphere, land, ice situations.
- The third image shows a listing of progress by the team on these many fronts.
- The fourth image shows the coupling required between the various software packages

Due to the four image limit per post I will present images related to a  BISICLES analysis for the West Antarctic including the FRIS (Weddell Sea), and the ASE (Amundsen Sea Embayment) ice shelves.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 09, 2013, 02:43:50 AM
The following images continue from the preceeding post with figures related to analysis for the Western Antarctic focused on the FRIS and ASE ice shelves:

- The first image addresses the BISICLES analysis focused on the PIG ice shelf.
- The second image shows the boundary layer conditions for such an analysis.
- The third images shows future/planned moving boundaries for such models to account for subglacial cavity growth and sub-ice-shelf melting.
- The fourth images shows ocean water bottom temperatures below the FRIS, together with deep averaged water velocities (below FRIS); showing that the ice shelf provides conditions that promote ice mass loss.

These images show how impressive the current efforts are made on this LCM analysis; but to me they emphasize  how much work remains to be done before projections from the combined GCM, RCM, and LCM efforts can be depended upon for reasonably accurate SLR projections.  I image that it will not be until the AR7 result are published that the projections may be close to being accurate for up to 2m of SLR, but that AR8 results may be required before the risks associated with 3 to 6m of SLR are reasonably quantified.  By that time the consequences will be irreversible.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 09, 2013, 04:30:28 PM
Here I provide a little bit of elaboration on my previous comment that global, regional and local circulation models (GCMs, RCMs, and LCMs; or preferably their Earth System Model equivalents), will not even be close to identifying the risks of abrupt SLR from the WAIS until AR8 (at the earliest), for reasons including many of the following points:

- The LCM projections for ocean water temperatures below the FRIS are significantly lower than the data (a couple of years old) that I show in other threads, probably because this LCM does not capture the warm CDW water introduced into the Filchner Trough via changes in the Weddell Gyre.  Thus the LCM projections for ice mass loss from the FRIS are no where near the local observed (in 2012) sub ice shelf melt rates of up to 7m/yr (that I cite in another thread).  As the ice mass loss from the FRIS has a major impact of the AABW production in this area, the ocean boundary conditioned introduced into this LCM run are also in error (as the low volume of AABW allows the volume of warm LCM to extend further south).

- The first image  shows the results of a convergence study for the LCM indicating that they need a resolution of at least 1 km which means that there model is too local to capture advective interactions between PIG and Thwaites (as I discuss in the "Surge" thread).  Thus computers will need to become bigger and faster before complex regional interactions can be captured.

- The second image shows the subglacial hydrological system used in the LCM which does not include geothermal heating comparable to that measured in the BSB (Byrd Subglacial Basin) that is creating relatively large volumes of basal meltwater, sufficient to feed a key subglacial lake, which is also not included in the LCM system.  Furthermore, I have postulated that the basal meltwater entering the ocean through the Thwaites Gateway Trough act as a positive feedback for the advective formation of a subglacial cavity in the trough (which is not captured in this LCM model).

- As I have run out of time once again, I will just re-post the third image from the "Philosophical" thread that shows my projection (for RCP 8.5 input) of the risk of abrupt SLR and how if this is the case, the fat tail under the probability curve increases with time (i.e. just because incomplete GCM, RCM and LCM models do not yet demonstrate to policy makers adequate concern for the risk of abrupt SLR, that does not mean that the relatively high risk of such an occurrence will not be identified in the future).
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 09, 2013, 07:24:16 PM
Model studies such as the following have been used to support the SLR projections to be published in AR5:
Ice-sheet model sensitivities to environmental forcing and their use in projecting future sea level (the SeaRISE project)
by Bindschadler et al 2013, Journal of Glaciology, Vol. 59, No. 214, doi:10.3189/2013JoG12J125

ABSTRACT. Ten ice-sheet models are used to study sensitivity of the Greenland and Antarctic ice sheets to prescribed changes of surface mass balance, sub-ice-shelf melting and basal sliding. Results exhibit a large range in projected contributions to sea-level change. In most cases, the ice volume above flotation lost is linearly dependent on the strength of the forcing. Combinations of forcings can be closely approximated by linearly summing the contributions from single forcing experiments, suggesting that nonlinear feedbacks are modest. Our models indicate that Greenland is more sensitive than Antarctica to likely atmospheric changes in temperature and precipitation, while Antarctica is more sensitive to increased ice-shelf basal melting. An experiment approximating the Intergovernmental Panel on Climate Change’s RCP8.5 scenario produces additional first-century contributions to sea level of 22.3 and 8.1cm from Greenland and Antarctica, respectively, with a range among models of 62 and 14 cm, respectively. By 200 years, projections increase to 53.2 and 26.7 cm, respectively, with ranges of 79 and 43 cm. Linear interpolation of the sensitivity results closely approximates these projections, revealing the
relative contributions of the individual forcings on the combined volume change and suggesting that total ice-sheet response to complicated forcings over 200 years can be linearized.

Such model projections emphasize that they expect linear relationships between the loss of ice Volume Above Floatation (VAF), which is the part of ice mass loss that contributes to eustatic SLR, and the strength of the  forcing.  Furthermore, they state that non-linear feedbacks between various forcings are modest; and therefore, they imply that they have high confidence in their SLR projections.  Indeed, within the limits of their model assumptions their statements are probably all true and appropriate; but they fail to identify the risks not captured by their models; which they leave to policy makers to access for themselves. 
As one small example of the limits of these AR5-level model projections for SLR can be gleamed from the four attached figures.  The first image shows a comparison of VAF by various models (note that: 100 Gt of ice mass loss ~ 0.28mm of Eustatic SLR) for both the GIS and the AIS.  Of the models reported the University of Maine Ice Sheet Model, UMISM, is most influence by basal melting changes, and while this basal melting effect is demonstrated to be significant in the UMISM projections for GIS; the study has omitted a similar run (with the basal melting effect turned on) for the AIS.  This is odd because according the second attached figure (of AIS ice velocities); the third attached image (of AIS basal melt water thickness) and the fourth image (of AIS basal temperatures, which do not include the recent measured WAIS Divide borehole basal temperatures that were found to be four to five times higher than previously thought) all taken from  the UMISM website, clearly indicate that the UMISM model for the AIS has been run with the basal melt effect turned on.  Thus it is likely to conclude that when these models eventually are upgraded to include the best science for subglacial hydrology, that their VAF loss projections for the AIS will increase significantly/nonlinearly.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 09, 2013, 09:40:35 PM
In order to better quantify the uncertainties of the SLR projections provided by the types of AR5 generation of LCM's that I have been discussion; the various teams need to do a more thorough job of documenting paleo-behavior of the WAIS and the EAIS during past interglacial periods, and then calibrating their respective models to match this historical behavior.  For example, the paleo-record (see the first attached image for any example from the PIG) undeniably documents the importance of the subglacial hydrology on the rate of ice mass loss from the AIS in the past; yet the AR5 generation of projections are inadequate to fully capture this response.  Furthermore, in my various posts in different threads I have repeated referred to projections for the PIG from model work by Gladstone et al, such as that reported in:

Earth and Planetary Science Letters Volumes 333–334, 1 June 2012, Pages 191–199, http://dx.doi.org/10.1016/j.epsl.2012.04.022, (http://dx.doi.org/10.1016/j.epsl.2012.04.022,) Calibrated prediction of Pine Island Glacier retreat during the 21st and 22nd centuries with a coupled flowline modelBy Rupert M. Gladstone et al.

Abstract
"A flowline ice sheet model is coupled to a box model for cavity circulation and configured for the Pine Island Glacier. An ensemble of 5000 simulations are carried out from 1900 to 2200 with varying inputs and parameters, forced by ocean temperatures predicted by a regional ocean model under the A1B ‘business as usual’ emissions scenario. Comparison is made against recent observations to provide a calibrated prediction in the form of a 95% confidence set. Predictions are for monotonic (apart from some small scale fluctuations in a minority of cases) retreat of the grounding line over the next 200 yr with huge uncertainty in the rate of retreat. Full collapse of the main trunk of the PIG during the 22nd century remains a possibility."

Here I repeat Gladestone et al's  point that huge uncertainties exist regarding the rate of retreat of the PIG over the next 200 years, and that a full collapse of the main trunk of the PIG, soon after 2100 is a possibility.  I also note that the as global warming is occurring at a faster rate than for any other period for several million years; this raises additional uncertainties.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 09, 2013, 09:52:32 PM
I forgot to post the attached (low quality) image from Gladestone et al 2012 (see previous post), documenting the risk that their model projects a risk that the PIG grounding line could retreat all the way to the WAIS divide shortly after 2100.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 09, 2013, 10:04:59 PM
Additional details of the approach and results from Gladestone's team can be found at:

Journal of Computational Physics; Volume 232, Issue 1, 1 January 2013, Pages 529–549, http://dx.doi.org/10.1016/j.jcp.2012.08.037 (http://dx.doi.org/10.1016/j.jcp.2012.08.037)
Adaptive mesh, finite volume modeling of marine ice sheets, by Stephen L. Cornford, Daniel F. Martin, Daniel T. Graves, Douglas F. Ranken, Anne M. Le Brocq, Rupert M. Gladstone, Antony J. Payne, Esmond G. Ng, William H. Lipscomb

Abstract
Continental scale marine ice sheets such as the present day West Antarctic Ice Sheet are strongly affected by highly localized features, presenting a challenge to numerical models. Perhaps the best known phenomenon of this kind is the migration of the grounding line — the division between ice in contact with bedrock and floating ice shelves — which needs to be treated at sub-kilometer resolution. We implement a block-structured finite volume method with adaptive mesh refinement (AMR) for three dimensional ice sheets, which allows us to discretize a narrow region around the grounding line at high resolution and the remainder of the ice sheet at low resolution. We demonstrate AMR simulations that are in agreement with uniform mesh simulations, but are computationally far cheaper, appropriately and efficiently evolving the mesh as the grounding line moves over significant distances. As an example application, we model rapid deglaciation of Pine Island Glacier in West Antarctica caused by melting beneath its ice shelf.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 13, 2013, 04:44:00 AM
With a range of estimated world population as high as that indicated by the attached image from a 2010 UN population projection; there must be a lot of uncertainty in determing probable anthropogenic input into GCM, RCM and LCm models.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 13, 2013, 08:06:21 PM
On May 9th, I made a post in this thread to which the following abstract and conclusions are relevant:

Paleo ice flow and subglacial meltwater dynamics in Pine Island Bay, West Antarctica By F. O. Nitsche et al (2013); The Cryosphere, 7, 249–262, 2013; www.the-cryosphere.net/7/249/2013/; (http://www.the-cryosphere.net/7/249/2013/;) doi:10.5194/tc-7-249-2013

Abstract: Increasing evidence for an elaborate subglacial drainage network underneath modern Antarctic ice sheets suggests that basal meltwater has an important influence on ice stream flow. Swath bathymetry surveys from previously glaciated continental margins display morphological features indicative of subglacial meltwater flow in inner shelf areas of some paleo ice stream troughs. Over the last few years several expeditions to the eastern Amundsen Sea embayment (West Antarctica) have investigated the paleo ice streams that extended from the Pine Island and Thwaites glaciers. A compilation of high-resolution swath bathymetry data from inner Pine Island Bay reveals details of a rough seabed topography including several deep channels that connect a series of basins. This complex basin and channel network is
indicative of meltwater flow beneath the paleo-Pine Island and Thwaites ice streams, along with substantial subglacial water inflow from the east. This meltwater could have enhanced ice flow over the rough bedrock topography. Meltwater features diminish with the onset of linear features north of the basins. Similar features have previously been observed in several other areas, including the Dotson-Getz Trough (western Amundsen Sea embayment) and Marguerite Bay (SW Antarctic Peninsula), suggesting that these features may be widespread around the Antarctic margin and that subglacial meltwater drainage played a major role in past ice-sheet dynamics.
…….
Conclusions:  This compilation of old and new swath bathymetry data from Pine Island Bay provides a coherent and detailed picture of a formerly glaciated inner continental shelf allowing more complete mapping and analysis of bedforms than previously available from discrete swath tracks. The resulting map reveals details that are critical for the understanding of past ice flow behaviour, subglacial processes and their spatial variability.  Our compilation confirms and extends the general zonation of erosional subglacial bedforms in crystalline bedrock on the inner shelf and subglacial depositional features on sedimentary substrate on the mid-shelf as previously identified by Lowe and Anderson (2002). Added here is a zone nearest the Pine Island Ice Shelf front characterised by smooth topography and showing up to 300m of sediments. This finding documents that sedimentary substrate on the inner shelf of Pine Island Bay is more widespread than previously thought. The complex pattern of rugged crystalline basement alternating with smooth sedimentary substrate in inner Pine Island Bay is consistent with observations under the modern Pine Island Glacier. The seafloor topography and sediment presence of inner Pine Island Bay indicate that post-LGM floating and partially grounded ice may have persisted in the area directly in front of the modern ice front for a longer time than in other parts of the Pine Island Trough system.  The orientation and location of the complex subglacial meltwater channel network suggest significant meltwater supply not only from Pine Island Glacier, but also from the Thwaites Glacier and from the Hudson Mountains. Meltwater volumes currently generated underneath the Pine Island and Thwaites glaciers would probably not be sufficient to generate the observed channel-basin network if discharged continuously. More likely this network was generated over several glacial cycles by episodic flow events caused by storage and release of meltwater through subglacial lakes, with possible additional contributions from subglacial volcanic eruptions.  Comparison of basin dimensions with those of modern subglacial lakes suggests that the active systems might be connected by channel networks resembling those in Pine Island Bay. The increasing number of paleo-meltwater features discovered by high-resolution swath bathymetry on different parts of the Antarctic continental margin provides a detailed, view of subglacial flow systems that should allow further consideration of related hydrodynamic processes and ice dynamics. A better understanding of the timing and nature of subglacial meltwater flow in Pine Island Bay will require more targeted sediment sampling from the large basins and channels, some beyond the range of standard piston coring, and improved sub-bottom or high-resolution seismic coverage of these features."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on June 18, 2013, 11:18:51 PM
The accompanying two figures are from the paper available at the following link.  While the paper (see below) has a lot of relevant information, I only present two images, and I note that this SeaRISE project analysis is only adequate to serve as a base case analysis for comparison to future analyses, and the variations between models in the current SeaRISE is too high.
Spatial Sensitivities of the Antarctic Ice Sheet to Environmental Changes: Insights from the SeaRISE Ice Sheet Modeling Project
by Nowicki et al 2013

http://www.pik-potsdam.de/~anders/publications/nowicki_bindschadler13a.pdf (http://www.pik-potsdam.de/~anders/publications/nowicki_bindschadler13a.pdf)

First image caption: Surface temperature (black) and precipitation (gray) anomalies over the Antarctic ice sheet corresponding to the IPCC AR4 A1B scenario, which form the basis of the SeaRISE atmospheric scenarios.

The information in this first image is a key assumption that merits comparison with future observations as they become available.

The second image caption: The change (experiment minus control) in the volume above flotation resulting from the suite of single forcings for eight regions of the Antarctic ice sheet after 100 simulated years. A) Atmospheric forcings: deltaVAF-C1 (blue), deltaVAF-C2 (red), deltaVAF-C3 (black). B) Basal sliding forcings: deltaVAF-S1 (blue), deltaVAF-S2 (red), deltaVAF-S3 (black). C) Oceanic forcings: deltaVAF-M1 (blue), deltaVAF-M2 (red), deltaVAF-M3 (black).

Note that deltaVAF is the change in grounded ice volume above floatation.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on June 28, 2013, 06:05:58 PM
The following information comes from an article that can be downloaded from:

http://doos.misu.su.se/pub/ballarotta_drijfhout_kuhlbrodt_doos_2013.pdf (http://doos.misu.su.se/pub/ballarotta_drijfhout_kuhlbrodt_doos_2013.pdf)

The residual circulation of the Southern Ocean: Which spatio-temporal scales
are needed?

by: Maxime Ballarotta, Sybren Drijfhout, Till Kuhlbrodt, & Kristofer Döös
Ocean Modelling 64 (2013) 46–55, Elsevier

The abstract for the paper is:
"The Southern Ocean circulation consists of a complicated mixture of processes and phenomena that arise at different time and spatial scales which need to be parametrized in the state-of-the-art climate models. The temporal and spatial scales that give rise to the present-day residual mean circulation are here investigated by calculating the Meridional Overturning Circulation (MOC) in density coordinates from an eddy-permitting global model. The region sensitive to the temporal decomposition is located between 38oS and 63oS, associated with the eddy-induced transport. The ‘‘Bolus’’ component of the residual circulation corresponds to the eddy-induced transport. It is dominated by timescales between 1 month and 1 year. The temporal behavior of the transient eddies is examined in splitting the ‘‘Bolus’’ component into a ‘‘Seasonal’’, an ‘‘Eddy’’ and an ‘‘Inter-monthly’’ component, respectively representing the correlation between density and velocity fluctuations due to the average seasonal cycle, due to mesoscale eddies and due to large-scale motion on timescales longer than one month that is not due to the seasonal cycle. The ‘‘Seasonal’’ bolus cell is important at all latitudes near the surface. The ‘‘Eddy’’ bolus cell is dominant in the thermocline between 50oS and 35oS and over the whole ocean depth at the latitude of the Drake Passage. The ‘‘Inter-monthly’’ bolus cell is important in all density classes and is maximal in the Brazil– Malvinas Confluence and the Agulhas Return Current. The spatial decomposition indicates that a large part of the Eulerian mean circulation is recovered for spatial scales larger than 11.25_, implying that small-scale meanders in the Antarctic Circumpolar Current (ACC), near the Subantarctic and Polar Fronts, and near the Subtropical Front are important in the compensation of the Eulerian mean flow."

In regards to the attached image the paper's summary states:

" The eddy-induced transport (‘‘Bolus’’ cell) extends between 40oS and 64oS and mostly counteracts the Eulerian circulation with 2–3 Sv (i.e. ~15%), except in two local maxima."

The caption for the attached image is:

Fig. 6. Longitudinal integral of total bolus transports at 39oS, 56oS, 60oS and 65oS integrated from the surface down to the 37 kg.m-3 isopycnal and (b) maps of the total bolus transport integrated from the surface down to the 37 kg m-3 isopycnal (a 10o running mean is applied for in the zonal integral).
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on July 02, 2013, 05:13:08 PM
The following reference concludes that there is no statistically significant historical evidence over the past 800 years to support the GCM/RCM model assumption that warming global temperatures will result in greater precipitation in Antarctica; and furthermore, concludes that any such increase in future precipitation in Antarctica "… could be offset by enhanced loss due to wind blowing ablation."  Therefore, from a risk point of view it is non-conservative to rely on a significant increase in future Antarctic precipitation from significantly limiting future AIS contributions to SLR.

A synthesis of the Antarctic surface mass balance during the last 800 yr
By: M. Frezzotti, C. Scarchilli, S. Becagli, M. Proposito, and S. Urbini
The Cryosphere, 7, 303–319, 2013; www.the-cryosphere.net/7/303/2013/; (http://www.the-cryosphere.net/7/303/2013/;) doi:10.5194/tc-7-303-2013

http://www.the-cryosphere.net/7/303/2013/tc-7-303-2013.pdf (http://www.the-cryosphere.net/7/303/2013/tc-7-303-2013.pdf)

Conclusions:

"A total of 67 SMB records from the AIS over the last 800 yr were analysed to assess the temporal variability of accumulation rates. The temporal and spatial variability of the SMB over the previous 800 yr indicates that SMB changes over most of Antarctica are statistically negligible and do not exhibit an overall clear trend. This result is in accordance with the results presented by Monaghan et al. (2006), which demonstrate statistically insignificant changes in the SMB over the past 50 yr. However, a clear increase in accumulation of more than 10% (>300 kgm−2 yr−1) has occurred in high- SMB coastal regions and over the highest part of the East Antarctic ice divide since the 1960s. The decadal records of previous centuries show that the observed increase in accumulation is not anomalous at the continental scale, that high accumulation periods also occurred during the 1370s and 1610s, and that the current SMB is not significantly different from that over the last 800 yr.  The differences in behaviour between the coastal/ice divide sites and the rest of Antarctica could be explained by the higher frequency of blocking anticyclones, which increase precipitation at coastal sites and lead to the advection of moist air at the highest areas, while blowing snow and/or erosion have reduced the SMB at windy sites. Eight hundred years of stacked SMB records mimic the total solar irradiance during the 13th and 18th centuries, suggesting a link between the southern Tropical Pacific and the atmospheric circulation in Antarctica through the generation and propagation of a large-scale atmospheric wave train.
Minor changes in the earth’s radiation budget may profoundly affect the atmospheric circulation and SMB of Antarctica. To predict future trends in the ice sheet mass balance, models must reliably reproduce the SMB patterns of the 2000s and the recent past (at the year-long and millennial scales). Future scenarios provided by global climate models suggest that Antarctic snow precipitation should increase in a warming climate but that snow accumulation is primarily driven by atmospheric circulation; these increases could be offset by enhanced loss due to wind blowing ablation."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on July 09, 2013, 05:15:43 PM
I would like to use the findings of the recent Ice2sea program (an overview report is available from the link below; as well as from the published results o substudies, which I will cite as I get to them) as an example of a well intended program, with excellent scientists, that has drifted into scientific reticence; and that could benefit from a hazard analysis conducted either by the administrators of the program (possibly by retaining hazard assessment consultants); or by fellow international researchers offering critiques of the findings.  I am posting in this thread as most of the Ice2sea findings are based on GCM/RCM models that have proved the old adage that: "All models are wrong, but some models are useful."

http://www.ice2sea.eu/ (http://www.ice2sea.eu/)

As I do not have very much time available in continuous periods, I plan to make a series of posts intended to highlight areas of hazards that the Ice2sea program have failed to identify/address, included (but not limited to):
- The fact that high atmospheric methane concentrations over Antarctica will keep circumpolar wind speeds in a critical area, while the ozone hole heals itself, which contributes to the continued upwelling of warm CDW that is directly melting Antarctic ice sheets and ice shelves.
- The researchers need to correctly model positive feedback mechanisms on top of the SRES A1B scenario that they use in order to capture such effects as: (a) the Arctic Sea Ice albedo flip leading to increased polar amplification; (b) the El Nino hiatus period advancing the introduction of OHC into the CDW several decades fasters than base models assume; (c) increased cyclonic activity in the Southern Ocean contributing to Ekman's pumping of warmer deep water to higher water elevations; (d) reduced AABW formation leading to a change in CDW circulation patterns, including the introduction of more CDW into the Weddell Gyre which leads to FRIS; and (e) the present increased Antarctic Sea Ice which is currently shielding local ocean water from the cooling affect of winter winds on the ocean water in the critical coastal regions, leading to high year-round ice melting due to advection beneath the floating ice.
- The critical and numerous local/regional oceanographic effects that can influence the ocean water ice melting interaction.

As I have run out of time now, I will post this and I will try to be more specific in subsequent posts.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on July 10, 2013, 12:44:02 AM
Regarding my critique of the Ice2sea finding, I would first like to note that a meaningful portion of the findings of the Ice2sea program was underpinned by work performed at the Alfred Wegener Institute; and therefore, I will begin my comments by addressing some points about the recent findings published in:

Southern Ocean warming and increased ice shelf basal melting in the 21st and 22nd centuries based on coupled ice-ocean finite-element modelling
by: R. Timmermann and H.H. Hellmer; Ocean Dynamics; Final version submitted on 26. June 2013.

The first attached image from Timmermann & Hellmer (T-H) presents some of their findings about both global and local (Southern Ocean) ocean water potential temperatures at the indicated depths and locations.  As one key example, I would particularly note that in their projected average potential temperatures for the Amundsen Sea Shelf drop rather significantly from 2012 to about 2070; which I find difficult to believe as: (a) the most recent physical measures indicate that the volume of warm CDW in this area is still increasing (see replay #11 in the "Trends of the Southern Ocean" thread), (b) the OHC below 2000 m depth globally (and in the Southern Ocean) has been increasing in recent years, and (c) the high atmospheric methane concentrations over the Antarctic continent appear to be maintaining the circumpolar wind velocities that have been driving warm CDW onto the Amundsen Sea Shelf (which T-H's model may be assuming will decrease as the ozone hole heals itself over Antarctica).

The second attached image is of T-H's projections of annual basal ice mass loss from the indicated ice features.  I believe that these projections are too, and as an example I look at the values that T-H project for the Pine Island Ice Shelf, PIIS.  For 2009 Rignot 2013 estimates that PIIS had average basal melt rates several times higher (see the third attached image) that reported by T-H for 2009 indicating that T-H has calibrated their model to result in too low of basal melt rates.  Furthermore, the T-M model do not consider ice calving.

Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on July 10, 2013, 01:21:07 AM
My replies #3,4, and 8 indicate the importance of a model to capture the influence of eddies; and it does not appear to me that the models used in the Ice2sea program have sufficient resolution to fully capture this important phenomenon.

Also, I previously mentioned that I do not believe that the Ice2sea models fully capture the influence of Ekman pumping (see attached images, note that Ekman Transport is to the left in the Southern Hemisphere and can induce Ekman pumping) from storm in the Southern Ocean on episodically delivering warm deep water to the Antarctic ice sheets and ice shelves.

I would also like to note that the Ice2sea models only deal with average ocean temperatures; while ice melts non-linearly with increasing temperatures; therefore, it is expected that the Ice2sea ice mass loss projections will be lower than reality because of this non-linear affect.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on July 10, 2013, 03:55:53 PM
I expect that this will be my last critique post about the Ice2sea program, as this program has sponsored much excellent research work (which I will discuss in other threads); but unfortunately due to the complexity of Antarctic SLR contributions the conclusions of the Ice2sea findings are unreasonably watered-down (ie scientific reticence has ignored any controversial loose ends) as is indicated by the first attached image from the Ice2sea 2013 summary report (also found in: An expert judgement assessment of future sea level rise from the ice sheetsJ. L. Bamber and W. P. Aspinall, 2013; Nature Climate Change; 3,  424–427; doi:10.1038/nclimate1778; which I have discussed in another thread).

Unfortunately, the Ice2sea expert elicitation of SLR contributions from WAIS, EAIS and GrIS, shown in the first attached image fails to capture the full risk of dynamic (and abrupt) SLR for reasons including:
(a) the precipitation model that they used to estimate snow accumulation in Antarctica is inappropriately biased by the few Atmospheric River events that occurred during the study; which as I have discussed previously either have a low probability of re-occurrence, or if they do re-occur frequently may likely fall as rain rather than as snow by the end of the century;
(b) As discussed in my immediately three preceeding posts, the GCM/RCM projections that they relied on are inaccurate due to: (i) inadequate refinement; (ii) failure to capture key feedback mechanisms; and (iii) failure to capture key boundary conditions and initial and future forcing functions.
(c) Regarding, the failure to capture key initial and future forcing functions, the Ice2sea program over relies on standard forcing functions such as for SRES A1B and E1 shown in the second attached image.  It appears that the over reliance upon these standard input has resulted in a failure to capture the high ocean heat uptake, OHT, measured from 2000 to 2013; and have not captured the measured high atmospheric methane concentrations over Antartica.
(d) Also, the Ice2sea models to not consider the very significant amounts of ice calving expected over the next few decades including the likely collapse of then Larsen C ice shelf (within ten years); large-scale calving from FRIS and RIS; and significant calving from almost all other ice shelves around Antarctica by the end of the century (as indicated by the calving and basal ice melting rates indicated by Rignot et al 2013).
(e) I believe that it is safe to say that the Ice2sea model projections for accelerating ice mass loss from the AIS are 75 to 100 years later than what is likely to actually occur; in the same manner as many GCM and RCM models did not project the Arctic Sea Ice to be seasonally absent until 2100, when in actuality this may occur by 2016 +/- 3yrs (which of course will contribute to a faster rate of Polar Amplification due to the expected Albedo Flip discussed by Hansen et al).

Again, after this post I will focus on the positive contributions of the Ice2sea program.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on July 20, 2013, 03:19:57 PM
Modeling ice calving of Antarctic ice shelves is fundamental to correctly modeling regional circulation models, RCMs.  Unfortunately, while good progress is being made (see the following reference & abstract and attached images) no adequate mathematical formulae exist for fully capturing the risks of abrupt ice-shelf retreat due to calving.

Kinematic First-Order Calving Law implies Potential for Abrupt Ice-Shelf Retreat
by: Anders Levermann, Torsten Albrecht, Ricarda Winkelmann, Maria A. Martin, Marianne Haseloff, and Ian Joughin; The Cryosphere, 2012

"Abstract. Recently observed large-scale disintegration of Antarctic ice shelves has moved their fronts closer towards grounded ice. In response, ice-sheet discharge into the ocean has accelerated, contributing to global sea-level rise and emphasizing the importance of calving-front dynamics.  The position of the ice front strongly influences the stress field within the entire sheet-shelf-system 5 and thereby the mass flow across the grounding line. While theories for an advance of the icefront are readily available, no general rule exists for its retreat, making it difficult to incorporate the retreat in predictive models. Here we extract the first-order large-scale kinematic contribution to calving which is consistent with large-scale observation. We emphasize that the proposed equation does not constitute a comprehensive calving law but represents the first order kinematic contribution 10 which can and should be complemented by higher order contributions as well as the influence of potentially heterogeneous material properties of the ice. When applied as a calving law, the equation naturally incorporates the stabilizing effect of pinning points and inhibits ice shelf growth outside of embayments. It depends only on local ice properties which are, however, determined by the full topography of the ice shelf. In numerical simulations the parameterization reproduces multiple 15 stable fronts as observed for the Larsen A and B Ice Shelves including abrupt transitions between them which may be caused by localized ice weaknesses. We also find multiple stable states of the Ross Ice Shelf at the gateway of the West Antarctic Ice Sheet with back stresses onto the sheet reduced by up to 90% compared to the present state."

The caption for the first attached image is:  "Fig. 1. Concept of eigen-calving - Panel a: Schematic illustrating proposed kinematic calving law: the calving rate is proportional to the spreading rates in both eigen-directions of the flow which generally coincide with directions along (green arrows) and perpendicular to (red arrows) the flow field. In confined region of the ice shelf, e.g. in the vicinity of the grounding line, convergence of ice flow perpendicular to the main flow direction yields closure of crevasses, inhibits large-scale calving and stabilizes the ice shelf. Near the mouth of the embayment, the flow field expansion occurs in both eigen-directions and large-scale calving impedes ice-shelf growth onto the open ocean. Panel b: The observed calving rate determined as the ice flow at the calving front increases with the product of the two eigenvalues which is proposed here as a first-order kinematic calving law in Eq. (1). Details on the data can be found in appendix."

The caption for the second attached image is: "Fig. 3. Eigencalving relation for the comparably broad topographies of Larsen-, Ronne- and Ross-ice shelves as derived from the surface velocity data set by Rignot et al. (2011)."

The caption for the third attached image is: "Fig. 4. Eigencalving relation for the comparably narrow topographies of Amery- and Filchner-ice shelves as derived from the surface velocity data set by Rignot et al. (2011)."

Such excellent work by Levermann et al 2012 highlight the calving risks to such key ice shelves as the Filchner Ice Shelf and Pine Island Ice Shelf; but they do not capture the risks from warming ocean water, storms, tides, etc that could rapidly accelerate such calving this century.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 04, 2013, 12:34:43 PM
The following reference/abstract, from the following link, indicate that according to the CMIP5 analysis for a high GHG scenario, that by 2100 there will be "…. a strong increase in the surface heat and freshwater fluxes in the ACC region. In contrast, the surface heat gain across the ACC region and the wind-driven surface transports are significantly correlated with an increased upper and decreased lower Eulerian mean meridional overturning circulation."

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-12-00504.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-12-00504.1)

Southern Ocean circulation and eddy compensation in CMIP5 models
by: Stephanie M. Downes & Andrew McC. Hogg; Journal of Climate 2013 ; e-View
doi: http://dx.doi.org/10.1175/JCLI-D-12-00504.1 (http://dx.doi.org/10.1175/JCLI-D-12-00504.1)

Abstract: "Thirteen state-of-the-art climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) are used to evaluate the response of the Antarctic Circumpolar Current (ACC) transport and Southern Ocean meridional overturning circulation to surface wind stress and buoyancy changes. Understanding how these flows – fundamental players in the global distribution of heat, gases and nutrients – respond to climate change is currently a widely debated issue among oceanographers. Here, we analyze the circulation responses of these coarse resolution coupled models to surface fluxes. Under a future CMIP5 climate pathway where the equivalent atmospheric CO2 reaches 1370 ppm by 2100, the models robustly project reduced Southern Ocean density in the upper 2000~m accompanied by strengthened stratification. Despite an overall increase in overlying wind stress (~20%), the projected ACC transports lie within ±15% of their historical state, and no significant relationship with changes in the magnitude or position of the wind stress is identified. The models indicate that a weakening of ACC transport at the end of the 21st century is correlated with a strong increase in the surface heat and freshwater fluxes in the ACC region. In contrast, the surface heat gain across the ACC region and the wind-driven surface transports are significantly correlated with an increased upper and decreased lower Eulerian mean meridional overturning circulation. The change in the eddy induced overturning in both depth and density space is quantified, and we find that the CMIP5 models project partial eddy compensation of the upper and lower overturning cells."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 07, 2013, 11:34:35 PM
The following reference discusses the risks and challenges of calibrating GCM projections for water vapor source conditions (including for Antarctica) based on paleoclimate reconstructions using deuterium excess as a tracer:

Lewis, S.C., A.N. LeGrande, M. Kelley, and G.A. Schmidt, 2013: Modeling insights into deuterium excess as an indicator of water vapor source conditions. J. Geophys. Res., 118, 243-262, doi:10.1029/2012JD017804.

"Deuterium excess (d) is interpreted in conventional paleoclimate reconstructions as a tracer of oceanic source region conditions, such as temperature, where precipitation originates. Previous studies have adopted coisotopic approaches (using both δ18O and d) to estimate past changes in both site and oceanic source temperatures for ice core sites using empirical relationships derived from conceptual distillation models, particularly Mixed Cloud Isotopic Models (MCIMs). However, the relationship between d and oceanic surface conditions remains unclear in past contexts. We investigate this climate-isotope relationship for sites in Greenland and Antarctica using multiple simulations of the water isotope-enabled Goddard Institute for Space Studies ModelE-R general circulation model and apply a novel suite of model vapor source distribution (VSD) tracers to assess d as a proxy for source temperature variability under a range of climatic conditions. Simulated average source temperatures determined by the VSDs are compared to synthetic source temperature estimates calculated using MCIM equations linking d to source region conditions. We show that although deuterium excess is generally a faithful tracer of source temperatures as estimated by the MCIM approach, large discrepancies in the isotope-climate relationship occur around Greenland during the Last Glacial Maximum simulation, when precipitation seasonality and moisture source regions were notably different from the present. This identified sensitivity in d as a source temperature proxy suggests that quantitative climate reconstructions from deuterium excess should be treated with caution for some sites when boundary conditions are significantly different from the present day. Also, the exclusion of the influence of humidity and other evaporative source changes in MCIM regressions may be a limitation of quantifying source temperature fluctuations from deuterium excess in some instances."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 08, 2013, 12:07:44 AM
This linked reference highlights the challenges of modeling (with GCMs and RCMs) the effects of ocean spray correctly:

http://onlinelibrary.wiley.com/doi/10.1029/2012JD018165/abstract (http://onlinelibrary.wiley.com/doi/10.1029/2012JD018165/abstract)

Tsigaridis, K., D. Koch, and S. Menon, 2013: Uncertainties and importance of sea spray composition on aerosol direct and indirect effects. J. Geophys. Res., 118, 220–235, doi:10.1029/2012JD018165.

"Although ocean-derived aerosols play a critical role in modifying the radiative balance over much of the Earth, their sources are still subject to large uncertainties, concerning not only their total mass flux but also their size distribution and chemical composition. These uncertainties are linked primarily to their source drivers, which is mainly wind speed, but are also linked to other factors, such as the presence of organic compounds in sea spray in addition to sea salt. In order to quantify these uncertainties and identify the larger knowledge gaps, we performed several model runs with online calculation of aerosol sources, removal, and underlying climate. In these simulations, both the direct and indirect aerosol effects on climate are included. The oceanic source of organic aerosols was found to be heavily dependent on the sea-salt parameterization selected. For only a factor of 2 change in assumed fine-mode sea-salt size, a factor of 10 difference in mass emissions was calculated for both sea salt and primary oceanic organics. The annual emissions of oceanic organics were calculated to range from 7.5 to 76 Tg/yr. The model's performance against remote oceanic measurements was greatly improved when including the high estimates of organics. However, the uncertainty could not be further reduced by bulk sea-salt measurements alone since most parameterizations tested agree reasonably well with measurements of both the (coarse-mode-dominated) sea salt and aerosol optical depth due to large changes in lifetime and optical properties of aerosols when different aerosol sizes are used."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 09, 2013, 11:20:15 PM
The linked reference indicates the risks and challenges of modeling the Southern Ocean:

http://nora.nerc.ac.uk/19162/ (http://nora.nerc.ac.uk/19162/)

Sallee, J.-B.; Shuckburgh, E.; Bruneau, N.; Meijers, A.J.S.; Bracegirdle, T.J.; Wang, Z.. 2013 Assessment of Southern Ocean mixed-layer depth in CMIP5 models: historical bias and forcing response. Journal of Geophysical Research: Oceans, 118 (4). 1845-1862. 10.1002/jgrc.20157

"Abstract/Summary
The development of the deep Southern Ocean winter mixed layer in the climate models participating in the fifth Coupled Models Intercomparison Project (CMIP5) is assessed. The deep winter convection regions are key to the ventilation of the ocean interior, and changes in their properties have been related to climate change in numerous studies. Their simulation in climate models is consistently too shallow, too light and shifted equatorward compared to observations. The shallow bias is mostly associated with an excess annual-mean freshwater input at the sea surface that over-stratifies the surface layer and prevents deep convection from developing in winter. In contrast, modeled future changes are mostly associated with a reduced heat loss in winter that leads to even shallower winter mixed layers. The mixed layers shallow most strongly in the Pacific basin under future scenarios, and this is associated with a reduction of the ventilated water volume in the interior. We find a strong state dependency for the future change of mixed-layer depth, with larger future shallowing being simulated by models with larger historical mixed-layer depths. Given that most models are biased shallow, we expect that most CMIP5 climate models might underestimate the future winter mixed-layer shallowing, with important implications for the sequestration of heat, and gases such as carbon dioxide, and therefore for climate."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 10, 2013, 12:40:07 AM
The following linked reference indicates that CMIP5 models project a strong positive trend for SAM when following the RCP 8.5 scenario; which implies increasing risk of strong ENSO's in the future (see discussion of the ACW interaction with the ENSO in the "Southern Ocean Trend" thread):

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-13-00204.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-13-00204.1)

 
Simulation and Projection of the Southern Hemisphere Annular Mode in CMIP5 Models
By: Fei Zheng, Jianping Li, Robin T. Clark, and Hyacinth C. Nnamchi; Journal of Climate 2013; doi: http://dx.doi.org/10.1175/JCLI-D-13-00204.1 (http://dx.doi.org/10.1175/JCLI-D-13-00204.1)


"Abstract
Climate variability in the Southern Hemisphere (SH) extratropical regions is dominated by the SH Annular Mode (SAM). Future changes in the SAM could have a large influence on climate over broad regions. In this paper, we utilized model simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5) to examine projected future changes in the SAM during the austral summer (DJF). To start off, we firstly assessed the ability of the models in reproducing the recently observed spatial and temporal variability. Twelve CMIP5 models examined were found to reproduce the SAM’s spatial pattern reasonably well in terms of both the symmetrical and the asymmetric component. The CMIP5 models show an improvement over CMIP3 in simulating the see-saw structure of the SAM, and also give improvements in the recently observed positive SAM trend. However, only half the models appeared to be able to capture two major recent decadal SAM phases. We then explored future SAM trends and its sensitivity to greenhouse gas (GHG) concentrations using simulations based on the representative concentration pathways RCP4.5 and 8.5. With the RCP4.5 we find a very weak negative trend for this century. Conversely, with the RCP8.5, a significant positive trend was projected, with a magnitude similar to the recent observed trend. Finally, we quantified model uncertainty in the future SAM projections by comparing projections from the individual CMIP5 models. The results imply the response of SH polar region stratospheric temperature to GHGs could be a significant controlling factor on the future evolution of the SAM."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 20, 2013, 12:01:11 AM
The following weblink provides access to a free pdf.  The reference and abstract indicate the changes and progress in adding the FRIS to a regional model of the Weddell Sea:

Coupling a thermodynamically active ice shelf to a regional simulation of the Weddell Sea; by: V. Meccia, I.Wainer, M. Tonelli, and E. Curchitser; Geosci. Model Dev., 6, 1209–1219, 2013; www.geosci-model-dev.net/6/1209/2013/; (http://www.geosci-model-dev.net/6/1209/2013/;) doi:10.5194/gmd-6-1209-2013

http://www.geosci-model-dev.net/6/1209/2013/gmd-6-1209-2013.pdf (http://www.geosci-model-dev.net/6/1209/2013/gmd-6-1209-2013.pdf)

"Abstract. A thermodynamically interactive ice shelf cavity parameterization is coupled to the Regional Ocean Model System (ROMS) and is applied to the Southern Ocean domain with enhanced resolution in the Weddell Sea. This implementation is tested in order to assess its degree of improvement to the hydrography (and circulation) of the Weddell Sea. Results show that the inclusion of ice shelf cavities in the model is feasible and somewhat realistic (considering the lack of under-ice observations for validation). Ice shelf–ocean interactions are an important process to be considered in order to obtain realistic hydrographic values under the ice shelf. The model framework presented in this work is a promising tool for analyzing the Southern Ocean’s response to future climate change scenarios."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 21, 2013, 03:56:09 PM
The following weblink leads to a free access summary paper addressing the challenges of a state-of-the-art Earth System Model ECHAM6 (from the Max Planck Institute):

http://onlinelibrary.wiley.com/doi/10.1002/jame.20015/full (http://onlinelibrary.wiley.com/doi/10.1002/jame.20015/full)

It may be another 20 years before such global models begin to capture key systems (in particular those associated with the Southern Ocean and the ice mass loss from the AIS) that can lead to ASLR by 2100; and until that time decision makers will be able to say that they do not see the risk of such abrupt climate response in the model projections.

Stevens, B., et al. (2013), Atmospheric component of the MPI-M Earth System Model: ECHAM6, J. Adv. Model. Earth Syst., 5, 146–172, doi:10.1002/jame.20015.

Abstract:
"ECHAM6, the sixth generation of the atmospheric general circulation model ECHAM, is described. Major changes with respect to its predecessor affect the representation of shortwave radiative transfer, the height of the model top. Minor changes have been made to model tuning and convective triggering. Several model configurations, differing in horizontal and vertical resolution, are compared. As horizontal resolution is increased beyond T63, the simulated climate improves but changes are incremental; major biases appear to be limited by the parameterization of small-scale physical processes, such as clouds and convection. Higher vertical resolution in the middle atmosphere leads to a systematic reduction in temperature biases in the upper troposphere, and a better representation of the middle atmosphere and its modes of variability. ECHAM6 represents the present climate as well as, or better than, its predecessor. The most marked improvements are evident in the circulation of the extratropics. ECHAM6 continues to have a good representation of tropical variability. A number of biases, however, remain. These include a poor representation of low-level clouds, systematic shifts in major precipitation features, biases in the partitioning of precipitation between land and sea (particularly in the tropics), and midlatitude jets that appear to be insufficiently poleward. The response of ECHAM6 to increasing concentrations of greenhouse gases is similar to that of ECHAM5. The equilibrium climate sensitivity of the mixed-resolution (T63L95) configuration is between 2.9 and 3.4 K and is somewhat larger for the 47 level model. Cloud feedbacks and adjustments contribute positively to warming from increasing greenhouse gases."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 23, 2013, 06:12:14 PM
The following linked reference (with a free access pdf) is both useful for upgrading Earth System Model, ESM, projections to include the best science on permafrost degradation; however, it also concludes that permafrost degradation will result in a drying of the thawed soil, which will contribute to sea level rise, and due to the fingerprint effect this will contribute more SLR to the Southern Ocean than to eustatic values, which will slightly contribute (note that according to National Geographic magazine Sept. 2013 ground ice and permafrost contain 71,970 cubic miles of water) to the destabilization of the WAIS.


http://onlinelibrary.wiley.com/doi/10.1002/jame.20045/pdf (http://onlinelibrary.wiley.com/doi/10.1002/jame.20045/pdf)


Simulating soil freeze/thaw dynamics with an improved pan-arctic water balance model;
by: M. A. Rawlins, D. J. Nicolsky, K. C. McDonald, and V. E. Romanovsky; 2013; JAMES, DOI: 10.1002/jame.20045


"Abstract
The terrestrial Arctic water cycle is strongly influenced by the presence of permafrost which is at present degrading as a result of warming. In this study we describe improvements to the representation of processes in the pan-Arctic Water Balance Model (PWBM) and evaluate simulated soil temperature at four sites in Alaska and active-layer thickness (ALT) across the pan-Arctic drainage basin. Model improvements include new parameterizations for thermal and hydraulic properties of organic soils; an updated snow model which accounts for seasonal changes in density and thermal conductivity; and a new soil freezing and thawing model which simulates heat conduction with phase change. When compared against observations across Alaska within differing landscape vegetation conditions in close proximity to one another, PWBM simulations show no systematic soil temperature bias. Simulated temperatures agree well with observations in summer. In winter results are mixed, with both positive and negative biases noted at times. In two pan-Arctic simulations forced with atmospheric reanalysis the model captures the mean in observed ALT although predictability as measured by correlation is limited. The geographic pattern in northern hemisphere permafrost area is well estimated. Simulated permafrost area differs from observed extent by 7 and 17% for the two model runs. Results of two simulations for the periods 1996–1999 and 2066–2069 for a single grid cell in central Alaska illustrate the potential for a drying of soils in the presence of increases in ALT, annual total precipitation and winter snowfall."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 23, 2013, 08:04:12 PM
The following linked reference emphasizes the need to use "high-order" models when trying to estimate ice mass loss from marine ice sheets (note that the only current marine ice sheet in the world is the WAIS); however, I do not believe that even these "high-order" models adequately capture ocean-ice interactions and stability issues such as the Jakobshavn or Thwaites Effects:


http://onlinelibrary.wiley.com/doi/10.1002/grl.50824/abstract (http://onlinelibrary.wiley.com/doi/10.1002/grl.50824/abstract)


Pattyn, F., and G. Durand (2013), Why marine ice sheet model predictions may diverge in estimating future sea level rise, Geophys. Res. Lett., 40, doi:10.1002/grl.50824.


Abstract:

"Despite major recent efforts, marine ice sheet models aiming at predicting future mass loss from ice sheets still suffer from uncertainties with respect to grounding line migration. A recent model intercomparison provided tools to test how models treat grounding line dynamics in a three-dimensional setting. Here we use these tools to address to what extent differences in mass loss occur according to the approximation to the Stokes equations, describing marine ice sheet flow, used. We find that models that neglect components of vertical shearing in the force budget wrongly estimate ice sheet mass loss by ±50% over century time scales when compared to models that solve the full Stokes system of equations. Models that only include horizontal stresses also misrepresent velocities and ice shelf geometry, suggesting that interactions between the grounded ice sheet and the ocean will also be modeled incorrectly. Based on these findings, we strongly advise the use of high-order models to compute reliable projections of ice sheet contribution to sea level rise."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 27, 2013, 08:10:21 PM
In June 2013 the newly established New Zealand Antarctic Research Institute (NZARI), announced new research projects - exploring everything from effects on key predators to the stratosphere, and the following extracts from the announcement are projects that might affect ice mass loss.  The results of these projects could provide significant input to RCM and LCM projections:


Assessing past, present and future polar amplification
Professor Tim Naish, Antarctic Research Centre - Victoria University of Wellington
The phenomenon of Polar Amplification occurs due to processes in the climate system that amplify the amount of warming in the high-latitudes compared to the global average. Polar amplification is a consistent feature of climate model projections, recent instrumental temperature observations, and model simulations and temperature reconstructions using geological archives of past warmer climates. It is of concern due to the effect of the warming on ice sheet stability and therefore global sea level, as well as carbon-cycle feedbacks such as those linked with permafrost thawing. We will produce a “state-of-play” synthesis of the current understanding of past, present and future polar amplification and its potential consequences.

Southern Ocean and Antarctic climate response to high atmospheric CO2 forcing
Dr Richard Levy, GNS Science and Dr Robert McKay, Antarctic Research Centre - Victoria University of Wellington NZARI has assembled an international team of past climate experts to study environmental conditions in New Zealand’s southern regions from a period in Earth’s past when CO2 concentrations were similar to those our planet will experience in the next five years. This team will examine rock and sediment cores obtained from beneath the Southern Ocean to determine how it changed as CO2 levels increased and what impact these changes had on Antarctica’s ice sheets.

A semi-empirical model of the stratosphere in the Antarctic climate system Dr. Greg Bodeker, Bodeker Scientific
We will develop a new method to simulate the evolution of the Antarctic ozone layer and its coupling to the southern high latitude climate system. The chemistry-climate models currently used to project changes in Antarctic ozone and its effects on climate are extremely computationally demanding and cannot provide ensembles of simulations spanning the range of uncertainty required for policy-relevant decision making. We will build a fast emulator of these complex models by extending a state-of-the-art simple climate model with a novel semi-empirical module that describes the key processes governing stratospheric ozone. This semi-empirical model is trained on real world observations.
 

Response of Bindshadler and MacAyeal Ice Stream grounding zone to iceberg calving events and implications for future change in West Antarctica.
Prof Christina Hulbe, School of Surveying - University of Otago
We propose to study ice shelf and grounding zone response to large iceberg calving at the eastern front of the Ross Ice Shelf using a combination of observational data and mathematical models. The location is ideal for this investigation because it has experienced recent change and the grounding line there is relatively close to the shelf front. The investigation will lead to improved understanding of time scales and magnitudes of response in a real, three-dimensional setting, an important objective for projecting change in West Antarctica on time scales of social relevance.


The following link provides additional information on these topics:


http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=10890402 (http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=10890402)

Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 31, 2013, 06:34:42 PM
The following linked reference indicates that it is vital to capture nonlinear dynamics within GCM projections (in this case for extreme precipitation projections).  Without appropriately capturing such nonlinear dynamics GCM projections will almost certainly continue to under estimate the likely consequences of increasing future radiative forcing:


http://onlinelibrary.wiley.com/doi/10.1002/hyp.9802/abstract (http://onlinelibrary.wiley.com/doi/10.1002/hyp.9802/abstract)


Panagoulia, D. and Vlahogianni, E. I. (2013), Nonlinear dynamics and recurrence analysis of extreme precipitation for observed and general circulation model generated climates. Hydrol. Process.; doi: 10.1002/hyp.9802


"Abstract
A statistical framework based on nonlinear dynamics theory and recurrence quantification analysis of dynamical systems is proposed to quantitatively identify the temporal characteristics of extreme (maximum) daily precipitation series. The methodology focuses on both observed and general circulation model (GCM) generated climates for present (1961–2000) and future (2061–2100) periods which correspond to 1xCO2 and 2xCO2 simulations. The daily precipitation has been modelled as a stochastic process coupled with atmospheric circulation. An automated and objective classification of daily circulation patterns (CPs) based on optimized fuzzy rules was used to classify both observed CPs and ECHAM4 GCM-generated CPs for 1xCO2 and 2xCO2 climate simulations (scenarios). The coupled model ‘CP-precipitation’ was suitable for precipitation downscaling. The overall methodology was applied to the medium-sized mountainous Mesochora catchment in Central-Western Greece. Results reveal substantial differences between the observed maximum daily precipitation statistical patterns and those produced by the two climate scenarios. A variable nonlinear deterministic behaviour characterizes all climate scenarios examined. Transitions’ patterns differ in terms of duration and intensity. The 2xCO2 scenario contains the strongest transitions highlighting an unusual shift between floods and droughts. The implications of the results to the predictability of the phenomenon are also discussed."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 31, 2013, 06:47:58 PM
The following linked reference indicates that some progress is being made in calibrating RCM's for the Southern Ocean, with regard to the projection of Antarctic sea ice volumes:


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-12-00139.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-12-00139.1)

 
Modeling the impact of wind intensification on Antarctic sea ice volume;
by: Jinlun Zhang, (2013); Journal of Climate 2013 ; e-View; doi: http://dx.doi.org/10.1175/JCLI-D-12-00139.1 (http://dx.doi.org/10.1175/JCLI-D-12-00139.1)



Abstract
"A global sea ice-ocean model is used to examine the impact of wind intensification on Antarctic sea ice volume. Based on the NCEP/NCAR reanalysis data, there are increases in surface wind speed (0.13% yr−1) and convergence (0.66% yr−1) over the ice-covered areas of the Southern Ocean during the period 1979-2010. Driven by the intensifying winds, the model simulates an increase in sea ice speed, convergence, and shear deformation rate, which produces an increase in ridge ice production in the Southern Ocean (1.1% yr−1). The increased ridged ice production is mostly in the Weddell, Bellingshausen, Amundsen, and Ross Seas where an increase in wind convergence dominates. The increase in ridging production contributes to an increase in the volume of thick ice (thickness > 2 m) in the Southern Ocean, while the volumes of thin ice (thickness ≤ 1 m) and medium thick ice (1 m < thickness ≤ 2 m) remain unchanged over the period 1979-2010. The increase in thick ice leads to an increase in ice volume in the Southern Ocean, particularly in the southern Weddell Sea where a significant increase in ice concentration is observed. The simulated increase in either the thick ice volume (0.91% yr−1) or total ice volume (0.46% yr−1) is significantly greater than other ice parameters (simulated or observed) such as ice extent (0.14–0.21% yr−1) or ice area fraction (0.24–0.28% yr−1), suggesting that ice volume is a potentially strong measure of change."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 31, 2013, 07:02:48 PM
The following linked reference indicates that the Southern Hemisphere's stratospheric stationary wave behavior will change as the assumed reduction in ozone depleting substances (ODSs) lead to a projected ozone recovery, while an assumed increase in GHGs lead to a projected eastward phase shift of the waves.  It is noted that this study does not evaluate the possible local increase of atmospheric methane over Antarctic (see the discussion in the "Methane" thread):

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-13-00160.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-13-00160.1)


Southern hemisphere stationary wave response to changes of ozone and greenhouse gases; by: Lei Wang; Paul J. Kushner; & Darryn W. Waugh; Journal of Climate 2013 ; e-View; doi: http://dx.doi.org/10.1175/JCLI-D-13-00160.1 (http://dx.doi.org/10.1175/JCLI-D-13-00160.1)


Abstract:
"The southern hemisphere (SH) stratospheric stationary wave amplitude increased significantly in late spring and early summer during the last two decades of the 20th century. To explore the underlying cause and the separate effects of anthropogenic forcing from ozone depleting substances (ODSs) and greenhouse gases (GHGs) in the past and projected SH stationary wave evolution, we examine a suite of chemistry climate model simulations. The model simulations produce trends in the wave amplitude similar to observed, although somewhat weaker. In simulations with changing ODSs, this increase in amplitude is reproduced during the ozone depletion period, and is reversed during the ozone recovery period. This response is related to changes in the strength and timing of the breakdown of the SH polar vortex associated with ozone depletion and recovery. GHG increases have little impact on the simulated stratospheric stationary wave amplitude, but are projected to induce an eastward phase shift of the waves. This phase shift is linked to the strengthening of the subtropical jets driven by GHG forcing via sea surface warming."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 31, 2013, 07:21:25 PM
The following linked reference discusses the challenges and progress being made in modeling Antarctic deglaciation:


Briggs, R., Pollard, D., and Tarasov, L.: A glacial systems model configured for large ensemble analysis of Antarctic deglaciation, The Cryosphere Discuss., 7, 1533-1589, doi:10.5194/tcd-7-1533-2013, 2013

This article is available from:

http://www.the-cryosphere-discuss.net/7/1533/2013/tcd-7-1533-2013.html (http://www.the-cryosphere-discuss.net/7/1533/2013/tcd-7-1533-2013.html)


The open access article & supplement are available as a PDF file from:

http://www.the-cryosphere-discuss.net/7/1533/2013/tcd-7-1533-2013.pdf (http://www.the-cryosphere-discuss.net/7/1533/2013/tcd-7-1533-2013.pdf)
http://www.the-cryosphere-discuss.net/7/1533/2013/tcd-7-1533-2013-supplement.pdf (http://www.the-cryosphere-discuss.net/7/1533/2013/tcd-7-1533-2013-supplement.pdf)

"Abstract. This article describes the Memorial University of Newfoundland/Penn State University (MUN/PSU) glacial systems model (GSM) that has been developed specifically for large-ensemble data-constrained analysis of past Antarctic Ice Sheet evolution. Our approach emphasizes the introduction of a large set of model parameters to explicitly account for the uncertainties inherent in the modelling of such a complex system.

At the core of the GSM is a 3-D thermo-mechanically coupled ice sheet model that solves both the shallow ice and shallow shelf approximations. This enables the different stress regimes of ice sheet, ice shelves, and ice streams to be represented. The grounding line is modelled through an analytical sub-grid flux parametrization. To this dynamical core the following have been added: a heavily parametrized basal drag component; a visco-elastic isostatic adjustment solver; a diverse set of climate forcings (to remove any reliance on any single method); tidewater and ice shelf calving functionality; and a new physically-motivated empirically-derived sub-shelf melt (SSM) component. To assess the accuracy of the latter, we compare predicted SSM values against a compilation of published observations. Within parametric and observational uncertainties, computed SSM for the present day ice sheet is in accord with observations for all but the Filchner ice shelf.

The GSM has 31 ensemble parameters that are varied to account (in part) for the uncertainty in the ice-physics, the climate forcing, and the ice-ocean interaction. We document the parameters and parametric sensitivity of the model to motivate the choice of ensemble parameters in a quest to approximately bound reality (within the limits of 31 parameters)."

Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on September 02, 2013, 01:56:25 AM
The findings of linked reference emphasize that it is critical to use more advanced RCMs when trying to project the transport of warm CDW across Antarctic continental shelves (to effect coastal bodies of ice); as the finding indicate that not only do wind affect the transport but also the production of AABW also affects this transport:

http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-12-0205.1 (http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-12-0205.1)


Stewart, Andrew L., Andrew F. Thompson, 2013: Connecting Antarctic Cross-Slope Exchange with Southern Ocean Overturning. J. Phys. Oceanogr., 43, pp 1453–1471.; doi: http://dx.doi.org/10.1175/JPO-D-12-0205.1 (http://dx.doi.org/10.1175/JPO-D-12-0205.1)


Abstract:
"Previous idealized investigations of Southern Ocean overturning have omitted its connection with the Antarctic continental shelves, leaving the influence of shelf processes on Antarctic Bottom Water (AABW) export unconsidered. In particular, the contribution of mesoscale eddies to setting the stratification and overturning circulation in the Antarctic Circumpolar Current (ACC) is well established, yet their role in cross-shelf exchange of water masses remains unclear. This study proposes a residual-mean theory that elucidates the connection between Antarctic cross-shelf exchange and overturning in the ACC, and the contribution of mesoscale eddies to the export of AABW. The authors motivate and verify this theory using an eddy-resolving process model of a sector of the Southern Ocean. The strength and pattern of the simulated overturning circulation strongly resemble those of the real ocean and are closely captured by the residual-mean theory. Over the continental slope baroclinic instability is suppressed, and so transport by mesoscale eddies is reduced. This suppression of the eddy fluxes also gives rise to the steep “V”-shaped isopycnals that characterize the Antarctic Slope Front in AABW-forming regions of the continental shelf. Furthermore, to produce water on the continental shelf that is dense enough to sink to the deep ocean, the deep overturning cell must be at least comparable in strength to wind-driven mean overturning on the continental slope. This results in a strong sensitivity of the deep overturning strength to changes in the polar easterly winds."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on September 02, 2013, 02:16:17 AM
The linked reference provides information on advances in modeling related to grounding line retreat for features (e.g. PIG) in the WAIS:

http://www.bristol.ac.uk/geography/people/tony-j-payne/pub/8420932 (http://www.bristol.ac.uk/geography/people/tony-j-payne/pub/8420932)


Cornford, SL, Martin, DF, Graves, DT, Ranken, DF, Brocq, AML, Gladstone, RM, Payne, AJ, Ng, EG & Lipscomb, WH 2013, ‘Adaptive mesh, finite volume modeling of marine ice sheets’. Journal of Computational Physics, vol 232., pp. 529-549

"Abstract
Continental scale marine ice sheets such as the present day West Antarctic Ice Sheet are strongly affected by highly localized features, presenting a challenge to numerical models. Perhaps the best known phenomenon of this kind is the migration of the grounding line the division between ice in contact with bedrock and floating ice shelves - which needs to be treated at sub-kilometer resolution. We implement a block-structured finite volume method with adaptive mesh refinement (AMR) for three dimensional ice sheets, which allows us to discretize a narrow region around the grounding line at high resolution and the remainder of the ice sheet at low resolution. We demonstrate AMR simulations that are in agreement with uniform mesh simulations, but are computationally far cheaper, appropriately and efficiently evolving the mesh as the grounding line moves over significant distances. As an example application, we model rapid deglaciation of Pine Island Glacier in West Antarctica caused by melting beneath its ice shelf."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on September 02, 2013, 02:25:24 AM
I find the following sentence from the linked reference rather chilling: "While the ACC transport may not accelerate significantly due to projected increases in along-ACC winds in future decades, significant changes in transport could still occur due to changes in the stress along the coast of Antarctica."

http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-13-091.1 (http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-13-091.1)

 
Acceleration of the Antarctic Circumpolar Current by Wind Stress Along the Coast of Antarctica; by: Jan D. Zika, Julien Le Sommer, Carolina O. Dufou,r Alberto Naveira-Garabato, Adam Blaker; Journal of Physical Oceanography 2013 ; e-View; doi: http://dx.doi.org/10.1175/JPO-D-13-091.1 (http://dx.doi.org/10.1175/JPO-D-13-091.1)

Abstract:
"The influence of wind forcing on the variability of the Antarctic Circumpolar Current (ACC) is investigated using a series of eddy-permitting ocean-sea-ice models. At inter-annual and decadal timescales the ACC transport is sensitive to both the mean strength of westerly winds along the ACC’s circumpolar path, consistent with zonal momentum balance theories, and sensitive to the wind stresses along the coast of Antarctica, consistent with the ‘free-mode’ theory of Hughes et al. (1999). A linear combination of the two factors explains differences in ACC transport across 11 regional quasi-equilibrium experiments. Repeated single-year global experiments show that the ACC can be robustly accelerated by both processes. Across an ensemble of simulations with realistic forcing over the second half of the 20th century, inter-annual ACC transport variability due to the free-mode mechanism exceeds that due to the zonal momentum balance mechanism by a factor of between 3.5 and 5 to one. While the ACC transport may not accelerate significantly due to projected increases in along-ACC winds in future decades, significant changes in transport could still occur due to changes in the stress along the coast of Antarctica."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on September 02, 2013, 02:42:15 AM
The linked reference discusses the results of simulations of several factors that significantly affect ice-shelf / ocean interaction (focused on grounding line retreat); and it identifies at least one set of circumstances that could possibly contribute to a negative feedback for ice mass loss:

http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-13-037.1 (http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-13-037.1)

 
Efficient flowline simulations of ice-shelf/ocean interactions: Sensitivity studies with a fully coupled model; by: Ryan T. Walker, David M. Holland, Byron R. Parizek, Richard B. Alley, Sophie M. J. Nowicki, Adrian Jenkins; Journal of Physical Oceanography 2013 ; doi: http://dx.doi.org/10.1175/JPO-D-13-037.1 (http://dx.doi.org/10.1175/JPO-D-13-037.1)


Abstract:
"Thermodynamic flowline and plume models for the ice-shelf/ocean system simplify the ice and ocean dynamics sufficiently to allow extensive exploration of parameters affecting ice-sheet stability while including key physical processes. Comparison between laboratory and geophysically based treatments of ice-ocean interface thermodynamics shows reasonable agreement between calculated melt rates, except where steep basal slopes and relatively high ocean temperatures are present. Results are especially sensitive to the poorly known drag coefficient, highlighting the need for additional field experiments to constrain its value. Our experiments also suggest that if the ice-ocean interface near the grounding line is steeper than some threshold, further steepening the slope may drive higher entrainment that limits buoyancy, slowing the plume and reducing melting; if confirmed, this will provide a stabilizing feedback on ice sheets under some circumstances."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on September 18, 2013, 10:29:52 PM
The following linked reference provide information required to help GCMs and RCMs to better model the influence of the Southern Ocean:

http://www.nature.com/nature/journal/v501/n7467/full/nature12432.html (http://www.nature.com/nature/journal/v501/n7467/full/nature12432.html)

(see also:  http://www.exeter.ac.uk/news/featurednews/title_320111_en.html (http://www.exeter.ac.uk/news/featurednews/title_320111_en.html) )

Rapid cross-density ocean mixing at mid-depths in the Drake Passage measured by tracer release;
by: Andrew J. Watson, James R. Ledwell, Marie-José Messias, Brian A. King, Neill Mackay, Michael P. Meredith, Benjamin Mills & Alberto C. Naveira Garabato; Nature; 501, 408–411doi:10.1038/nature1243218 September 2013

Abstract:
"Diapycnal mixing (across density surfaces) is an important process in the global ocean overturning circulation. Mixing in the interior of most of the ocean, however, is thought to have a magnitude just one-tenth of that required to close the global circulation by the downward mixing of less dense waters. Some of this deficit is made up by intense near-bottom mixing occurring in restricted ‘hot-spots’ associated with rough ocean-floor topography, but it is not clear whether the waters at mid-depth, 1,000 to 3,000 metres, are returned to the surface by cross-density mixing or by along-density flows. Here we show that diapycnal mixing of mid-depth (~1,500 metres) waters undergoes a sustained 20-fold increase as the Antarctic Circumpolar Current flows through the Drake Passage, between the southern tip of South America and Antarctica. Our results are based on an open-ocean tracer release of trifluoromethyl sulphur pentafluoride. We ascribe the increased mixing to turbulence generated by the deep-reaching Antarctic Circumpolar Current as it flows over rough bottom topography in the Drake Passage. Scaled to the entire circumpolar current, the mixing we observe is compatible with there being a southern component to the global overturning in which about 20 sverdrups (1 Sv = 106 m3 s−1) upwell in the Southern Ocean, with cross-density mixing contributing a significant fraction (20 to 30 per cent) of this total, and the remainder upwelling along constant-density surfaces. The great majority of the diapycnal flux is the result of interaction with restricted regions of rough ocean-floor topography."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on September 19, 2013, 01:57:10 AM
In the following linked reference the authors write: "... the Southern Ocean is the dominant anthropogenic carbon sink of the world's oceans and plays a central role in the redistribution of physical and biogeochemical properties around the globe," and they therefore state that "one of the most pressing issues in oceanography is to understand the rate, the structure and the controls of the water mass overturning circulation in the Southern Ocean and to accurately represent these aspects in climate models."


http://onlinelibrary.wiley.com/doi/10.1002/jgrc.20135/abstract (http://onlinelibrary.wiley.com/doi/10.1002/jgrc.20135/abstract)

Sallée, J.-B., E. Shuckburgh, N. Bruneau, A. J. S. Meijers, T. J. Bracegirdle, Z. Wang, and T. Roy (2013), Assessment of Southern Ocean water mass circulation and characteristics in CMIP5 models: Historical bias and forcing response, J. Geophys. Res. Oceans, 118, 1830–1844 doi:10.1002/jgrc.20135.

Abstract:
"The ability of the models contributing to the fifth Coupled Models Intercomparison Project (CMIP5) to represent the Southern Ocean hydrological properties and its overturning is investigated in a water mass framework. Models have a consistent warm and light bias spread over the entire water column. The greatest bias occurs in the ventilated layers, which are volumetrically dominated by mode and intermediate layers. The ventilated layers have been observed to have a strong fingerprint of climate change and to impact climate by sequestrating a significant amount of heat and carbon dioxide. The mode water layer is poorly represented in the models and both mode and intermediate water have a significant fresh bias. Under increased radiative forcing, models simulate a warming and lightening of the entire water column, which is again greatest in the ventilated layers, highlighting the importance of these layers for propagating the climate signal into the deep ocean. While the intensity of the water mass overturning is relatively consistent between models, when compared to observation-based reconstructions, they exhibit a slightly larger rate of overturning at shallow to intermediate depths, and a slower rate of overturning deeper in the water column. Under increased radiative forcing, atmospheric fluxes increase the rate of simulated upper cell overturning, but this increase is counterbalanced by diapycnal fluxes, including mixed-layer horizontal mixing, and mostly vanishes."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on December 14, 2013, 02:21:42 AM
I believe that the limited amount of projected Antarctic contribution to SLR indicated in the linked (and cited) article from the SeaRISE project; demonstrates the limitations of current regional circulation models:

http://www.earth-syst-dynam-discuss.net/4/1117/2013/esdd-4-1117-2013.pdf (http://www.earth-syst-dynam-discuss.net/4/1117/2013/esdd-4-1117-2013.pdf)

Levermann, A., Winkelmann, R., Nowicki, S., Fastook, J. L., Frieler, K., Greve, R., Hellmer, H. H., Martin, M. A., Mengel, M., Payne, A. J., Pollard, D., Sato, T., Timmermann, R., Wang, W. L., and Bindschadler, R. A.: Projecting Antarctic ice discharge using response functions from SeaRISE ice-sheet models, Earth Syst. Dynam. Discuss., 4, 1117-1168, doi:10.5194/esdd-4-1117-2013, 2013.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on January 06, 2014, 10:17:09 PM
The following linked article indicates some of the importance and complexities of modeling the Antarctic/Southern-Ocean circulation systems:

http://www.ibtimes.com/antarctica-key-driver-global-climate-south-pole-temperatures-affect-rest-planet-1528414 (http://www.ibtimes.com/antarctica-key-driver-global-climate-south-pole-temperatures-affect-rest-planet-1528414)
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on January 23, 2014, 01:29:15 AM
The linked article indicates that warming of the north and tropical Atlantic Ocean is reducing the atmospheric pressure and the sea ice offshore of the Amundsen Sea Embayment, in a manner that may have adverse consequences for SLR:

Xichen Li, David M. Holland, Edwin P. Gerber & Changhyun Yoo, (2014), "Impacts of the north and tropical Atlantic Ocean on the Antarctic Peninsula and sea ice"; Nature; 505, 538–542; doi:10.1038/nature12945

http://www.nature.com/nature/journal/v505/n7484/full/nature12945.html (http://www.nature.com/nature/journal/v505/n7484/full/nature12945.html)

Abstract: "In recent decades, Antarctica has experienced pronounced climate changes. The Antarctic Peninsula exhibited the strongest warming of any region on the planet, causing rapid changes in land ice. Additionally, in contrast to the sea-ice decline over the Arctic, Antarctic sea ice has not declined, but has instead undergone a perplexing redistribution. Antarctic climate is influenced by, among other factors, changes in radiative forcing and remote Pacific climate variability, but none explains the observed Antarctic Peninsula warming or the sea-ice redistribution in austral winter. However, in the north and tropical Atlantic Ocean, the Atlantic Multidecadal Oscillation (a leading mode of sea surface temperature variability) has been overlooked in this context. Here we show that sea surface warming related to the Atlantic Multidecadal Oscillation reduces the surface pressure in the Amundsen Sea and contributes to the observed dipole-like sea-ice redistribution between the Ross and Amundsen–Bellingshausen–Weddell seas and to the Antarctic Peninsula warming. Support for these findings comes from analysis of observational and reanalysis data, and independently from both comprehensive and idealized atmospheric model simulations. We suggest that the north and tropical Atlantic is important for projections of future climate change in Antarctica, and has the potential to affect the global thermohaline circulation and sea-level change."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on January 23, 2014, 04:09:51 PM
It has been a while since I posted the attached figure from Bertler et al 2006 (see reference at bottom of this post), which shows pictorially the relationship between the location of the Amundsen Sea Low (or Amundsen Bellingshausen Sea Low), ASL (or ABSL) and either a La Nina or an El Nino event.  Taken together with the information in my immediately preceding post (which stated that sea surface warming related to the Atlantic Multidecadal Oscillation, AMO, reduces the surface pressure in the Amundsen Sea), this implies that when the next El Nino event occurs (which may be the austral summer of 2014 to 2015) and shifts the location of the ASL to blow wind directly into the ASE, the winds will likely be stronger due to the lower Amundsen sea pressure associated with AMO effect; which will drive more warm CDW into the ASE resulting in higher than previously expected ice mass loss from the glaciers in this area.

Bertler, N.A., Naish, T.T., Mayewski, P.A. and Barrett, P.J., (2006), "Opposing oceanic and atmospheric ENSO influences on the Ross Sea Region, Antarctica", Advances in Geosciences, 6, pp 83-88, SRef-ID: 1680-7359/adgeo/2006-6-83.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on January 24, 2014, 04:17:16 PM
The following link leads to a nice summary (from October 2013) of the ARGO findings through the end of 2012:

http://ceres.larc.nasa.gov/documents/STM/2013-10/14_Global_averages.pdf (http://ceres.larc.nasa.gov/documents/STM/2013-10/14_Global_averages.pdf)

As indicated in the attached figure, one key finding is that all of the ocean heat gain in the ARGO era has been in the Southern Hemisphere (which indicates that all of the steric SLR in in the ARGO era has been in the Southern Hemisphere).  This provides additional support to my position that when the current EL Nino hiatus period ends, there is an excess of heat in the Southern Ocean that can accelerate ice mass loss from Antarctica once the local winds/current shift sufficiently to increase the ocean interaction with the grounded ice.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on January 27, 2014, 07:11:55 PM
Articles such as that found at the link below, indicate that science is only now beginning to delineate the nature of a deep ocean current 40-times larger than the Amazon in the critical area near the Kerguelen Plateau in the Southern Ocean.  These finding indicate that the flows and velocities are higher than previously expected, indicating the relatively high degree of uncertainty associated with Regional Circulation Models of the Southern Ocean; which indicates an associated lower confidence level in sea level rise projections, than previously acknowledged in reports such as the AR5:

http://www.worldbulletin.net/science-technology/57641/scientists-uncover-deep-ocean-current-near-antarctica (http://www.worldbulletin.net/science-technology/57641/scientists-uncover-deep-ocean-current-near-antarctica)
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on January 31, 2014, 10:18:51 PM
The linked AGU poster discusses the influence of the ozone hole over Antarctica and the impact of the SAM on cross shelf heat exchange around Antarctica:

Yoo, C., E. P. Gerber, L.-S. Bai, D. H. Bromwich, M. S. Dinniman, K. M. Hines, D. M. Holland, and J. M. Klinck: Impact of Souther Annular Mode on cross shelf exchange around the Antarctica. 2013 AGU Fall Meeting, San Francisco, CA, Dec. 9-13, 2013.

http://polarmet.osu.edu/ACCIMA/ACCIMA_yoo_etal_201312.pdf (http://polarmet.osu.edu/ACCIMA/ACCIMA_yoo_etal_201312.pdf)
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on February 01, 2014, 08:13:16 PM
The linked (free access) paper describes progress being made on the Regional Ocean Model System (ROMS) focused on the Southern Ocean (& in this case study the Weddell Sea).  This work confirms the importance of including ice-ocean coupling within RCMs:

V. Meccia, I.Wainer, M. Tonelli, and E. Curchitser, (2013), "Coupling a thermodynamically active ice shelf to a regional simulation of the Weddell Sea", Geosci. Model Dev., 6, 1209–1219, 2013, www.geosci-model-dev.net/6/1209/2013/; (http://www.geosci-model-dev.net/6/1209/2013/;) doi:10.5194/gmd-6-1209-2013

http://www.geosci-model-dev.net/6/1209/2013/gmd-6-1209-2013.pdf (http://www.geosci-model-dev.net/6/1209/2013/gmd-6-1209-2013.pdf)

"Abstract. A thermodynamically interactive ice shelf cavity parameterization is coupled to the Regional Ocean Model System (ROMS) and is applied to the Southern Ocean domain with enhanced resolution in the Weddell Sea. This implementation is tested in order to assess its degree of improvement to the hydrography (and circulation) of the Weddell Sea. Results show that the inclusion of ice shelf cavities in the model is feasible and somewhat realistic (considering the lack of under-ice observations for validation). Ice shelf–ocean interactions are an important process to be considered in order to obtain realistic hydrographic values under the ice shelf. The model framework presented in this work is a promising tool for analyzing the Southern Ocean’s response to future climate change scenarios."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on February 01, 2014, 08:31:00 PM
Papers such as the linked article by Sigmond et al 2014, indicate that the current CMIP5 results (which do not simulated the observed sea ice pattern in Antarctica) have not had time to incorporate the findings of Li et al 2014 (see reference at end of post) of how the north and tropical Atlantic Ocean influences sea ice in the Southern Ocean.  It will take time (decades)  to correctly calibrate the current generation of GCMs and RCMs.

Sigmond, Michael, John C. Fyfe, 2014: The Antarctic Sea Ice Response to the Ozone Hole in Climate Models. J. Climate, 27, 1336–1342.  doi: http://dx.doi.org/10.1175/JCLI-D-13-00590.1 (http://dx.doi.org/10.1175/JCLI-D-13-00590.1)

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-13-00590.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-13-00590.1)

Abstract: "It has been suggested that the increase of Southern Hemisphere sea ice extent since the 1970s can be explained by ozone depletion in the Southern Hemisphere stratosphere. In a previous study, the authors have shown that in a coupled atmosphere–ocean–sea ice model the ozone hole does not lead to an increase but to a decrease in sea ice extent. Here, the robustness of this result is established through the analysis of models from phases 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5). Comparison of the mean sea ice trends in CMIP3 models with and without time-varying stratospheric ozone suggests that ozone depletion is associated with decreased sea ice extent, and ozone recovery acts to mitigate the future sea ice decrease associated with increasing greenhouse gases. All available historical simulations with CMIP5 models that were designed to isolate the effect of time-varying ozone concentrations show decreased sea ice extent in response to historical ozone trends. In most models, the historical sea ice extent trends are mainly driven by historical greenhouse gas forcing, with ozone forcing playing a secondary role."

Xichen Li, David M. Holland, Edwin P. Gerber & Changhyun Yoo, (2014), "Impacts of the north and tropical Atlantic Ocean on the Antarctic Peninsula and sea ice"; Nature; 505, 538–542; doi:10.1038/nature12945
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on February 03, 2014, 05:12:53 PM
The following link leads to a pdf of New Zealand's Antarctic Science program for 2013-2014.  The Kiwis are doing a lot of great science relevant to SLR, including: (a) K049: Roosevelt Island Climate Evolution – RICE Project; (b) K055: Assessment of the Current State of the Antarctic Middle Atmosphere and Climate Model Validation; (c) K060: Space Weather Monitoring (AARDDVARK), (d) K063: Antarctic sea ice thickness mapping at McMurdo Sound, and (e) K085: Investigating ozone depletion and climate change: trace gas measurements in the Antarctic atmosphere:

http://antarcticanz.govt.nz/images/downloads/science/Science_Programme-201314.pdf (http://antarcticanz.govt.nz/images/downloads/science/Science_Programme-201314.pdf)
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on February 04, 2014, 01:29:43 AM
The following link cites the findings of field work by the Alfred Wegener Institute where the researchers took marine sediment cores from the Pacific sector of the Southern Ocean (the Pacific Sector accounts for 50% of the Southern Ocean), that records about 1 million year worth of dust deposition on the seafloor.  This is significant because during past ice ages the dust over the Southern Ocean increased by about 3-times normal; and the calibration of past GCMs over the past 1 million years assumed that there should be very little dust in the Pacific sector of the Southern Ocean during past ice ages, while the cores should that the amounts and origins of the dust in the Pacific sector was the same in the other sectors of the Southern Ocean.  This implies that during these past ice age periods, large band of westerly winds extended so far northward that they gather dust from Australia and New Zealand (as well as the previously recognized dust source from Argentina).  This implies that all existing GCMs need to be re-calibrated so that they project the occurrence of this large band of westerly wind during past ice ages:

F. Lamy, R. Gersonde, G. Winckler, O. Esper, A. Jaeschke, G. Kuhn, J. Ullermann, A. Martinez-Garcia, F. Lambert, & R. Kilian, (2014), "Increased Dust Deposition in the Pacific Southern Ocean During Glacial Periods", Science 24 January 2014: Vol. 343 no. 6169 pp. 403-407, DOI: 10.1126/science.1245424

http://environmentalresearchweb.org/cws/article/yournews/56052 (http://environmentalresearchweb.org/cws/article/yournews/56052)
http://www.sciencemag.org/content/343/6169/403.short (http://www.sciencemag.org/content/343/6169/403.short)

Abstract: "Dust deposition in the Southern Ocean constitutes a critical modulator of past global climate variability, but how it has varied temporally and geographically is underdetermined. Here, we present data sets of glacial-interglacial dust-supply cycles from the largest Southern Ocean sector, the polar South Pacific, indicating three times higher dust deposition during glacial periods than during interglacials for the past million years. Although the most likely dust source for the South Pacific is Australia and New Zealand, the glacial-interglacial pattern and timing of lithogenic sediment deposition is similar to dust records from Antarctica and the South Atlantic dominated by Patagonian sources. These similarities imply large-scale common climate forcings, such as latitudinal shifts of the southern westerlies and regionally enhanced glaciogenic dust mobilization in New Zealand and Patagonia."

Editor's Summary: "The effect of windblown dust on marine productivity in the Southern Ocean is thought to be a key determinant of atmospheric CO2 concentrations. Lamy et al. (p. 403) present a record of dust supply to the Pacific sector of the Southern Ocean for the past one million years, derived from a suite of deep-sea sediment cores. Dust deposition during glacial periods was 3 times greater than during interglacials, and its major source region was probably Australia or New Zealand."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: sidd on February 04, 2014, 01:38:29 AM
Interesting. I wonder if dust induced phytoplankton bloom played a part in increasing CO2 drawdown during glacials.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on February 04, 2014, 01:43:35 AM
sidd,

Yes, the article clearly states that the iron rich dust causes the plankton in the Southern Ocean to bloom which decreased atmospheric carbon dioxide levels during past ice ages (resulting in a feedback for addition cooling).

Best,
ASLR
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on February 04, 2014, 06:43:56 PM
The linked reference discusses how animal-borne instruments have improved estimates of the Southern Ocean general circulation over the last decade:

Roquet, F., et al. (2013), Estimates of the Southern Ocean general circulation improved by animal-borne instruments, Geophys. Res. Lett., 40, 6176–6180, doi:10.1002/2013GL058304.

http://onlinelibrary.wiley.com/doi/10.1002/2013GL058304/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2013GL058304/abstract)

Abstract
"Over the last decade, several hundred seals have been equipped with conductivity-temperature-depth sensors in the Southern Ocean for both biological and physical oceanographic studies. A calibrated collection of seal-derived hydrographic data is now available, consisting of more than 165,000 profiles. The value of these hydrographic data within the existing Southern Ocean observing system is demonstrated herein by conducting two state estimation experiments, differing only in the use or not of seal data to constrain the system. Including seal-derived data substantially modifies the estimated surface mixed-layer properties and circulation patterns within and south of the Antarctic Circumpolar Current. Agreement with independent satellite observations of sea ice concentration is improved, especially along the East Antarctic shelf. Instrumented animals efficiently reduce a critical observational gap, and their contribution to monitoring polar climate variability will continue to grow as data accuracy and spatial coverage increase."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on February 05, 2014, 12:33:14 AM
The following link leads to an article indicating that NOAA and the U.S. Navy are teaming up with academic and other government scientists to design the next generation of powerful supercomputer models to predict weather, ocean conditions and regional climate change:

http://research.noaa.gov/News/NewsArchive/LatestNews/TabId/684/ArtMID/1768/ArticleID/10430/NOAA-launches-research-on-next-generation-of-high-performance-weather-climate-models.aspx (http://research.noaa.gov/News/NewsArchive/LatestNews/TabId/684/ArtMID/1768/ArticleID/10430/NOAA-launches-research-on-next-generation-of-high-performance-weather-climate-models.aspx)
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on March 03, 2014, 11:06:58 PM
The following linked reference (with a free access pdf) discusses the new ACCIMA regional climate system model for the Southern Ocean and Antarctica.  This model contains numerous improvements on earlier models, but still needs improvement:

Bromwich, D. H, C. Yoo, K. M. Hines, L.-S. Bai, D. Holland, J. Klinck, M. Dinniman, and E. Gerber, 2014: ACCIMA: A regional climate system model for the Southern Ocean and Antarctica. J. Climate,


http://polarmet.osu.edu/ACCIMA/bromwich_yoo_jc_2014.pdf (http://polarmet.osu.edu/ACCIMA/bromwich_yoo_jc_2014.pdf)

Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: wili on March 06, 2014, 02:40:24 AM

The Antarctic Half of the Global Thermohaline Circulation is Collapsing

http://www.dailykos.com/story/2014/03/05/1281907/-The-Antarctic-Half-of-the-Global-Thermohaline-Circulation-is-Collapsing (http://www.dailykos.com/story/2014/03/05/1281907/-The-Antarctic-Half-of-the-Global-Thermohaline-Circulation-is-Collapsing)

Quote
The largest source of Antarctic Bottom Water in the global thermohaline circulation (labelled W) has ceased production.

...this study probably underestimates the amount of fresh water around Antarctica and its effects on Antarctic Bottom Water (ABW) formation...

 Global political policies are not keeping up with the rate of change and our models have, to date, underestimated the rate of change. We are witnessing a total failure of global leadership to deal with changes we caused that are spiraling out of control.

Peter Ward on the consequences of this development: "When [the global ocean current conveyor belt] stops, we lose oxygen at the bottom, and we start the process toward mass extinction."

http://climatestate.com/2014/03/05/the-antarctic-half-of-the-global-thermohaline-circulation-is-collapsing/ (http://climatestate.com/2014/03/05/the-antarctic-half-of-the-global-thermohaline-circulation-is-collapsing/)
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on March 06, 2014, 03:46:54 PM
wili,

The topic of the AABW is a serious matter and has been discussed extensively, in many different threads in the Antarctic folder; but rather than referencing these past discussions, I will limit myself now to noting that the following research by Rose et al. (2014) indicates that ocean heat uptake (OHU) in the polar regions has three times the influence on climate sensitivity as does the same OHU in the tropics.  This implies that the reduction in OHU into the AABW will have an amplified effect on global warming:

Rose BEJ, KC Armour, DS Battisti, N Feldl and DDB Koll (2014) The dependence of transient climate sensitivity and radiative feedbacks on the spatial pattern of ocean heat uptake, Geophysical Research Letters, 41, doi: 10.1002/2013GL058955

http://web.mit.edu/karmour/www/Rose_etal_GRL2014.pdf (http://web.mit.edu/karmour/www/Rose_etal_GRL2014.pdf)

Abstract: "The effect of ocean heat uptake (OHU) on transient global warming is studied in a multimodel framework. Simple heat sinks are prescribed in shallow aquaplanet ocean mixed layers underlying atmospheric general circulation models independently and combined with CO2 forcing. Sinks are localized to either tropical or high latitudes, representing distinct modes of OHU found in coupled simulations.  Tropical OHU produces modest cooling at all latitudes, offsetting only a fraction of CO2 warming. High latitude OHU produces three times more global mean cooling in a strongly polar-amplified pattern. Global sensitivities in each scenario are set primarily by large differences in local shortwave cloud feedbacks, robust across models. Differences in atmospheric energy transport set the pattern of temperature change.  Results imply that global and regional warming rates depend sensitively on regional ocean processes setting the OHU pattern, and that equilibrium climate sensitivity cannot be reliably estimated from transient observations."

Best,
ASLR
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on April 25, 2014, 05:22:27 PM
The following link leads to a free access pdf of a paper about the findings of a regional circulation model that focuses on basal ice melting for Antarctic ice shelves (& include atmospheric effects):

http://polarmet.osu.edu/ACCIMA/dinniman_klinck_jc_2014.pdf (http://polarmet.osu.edu/ACCIMA/dinniman_klinck_jc_2014.pdf)
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on April 25, 2014, 05:27:49 PM
The following link leads to a free access pdf of the Bromwich et al 2014 paper entitled: "ACCIMA: A Regional Climate System Model for the Southern Ocean and Antarctica"; which of course is about the ACCIMA RCM:

http://polarmet.osu.edu/ACCIMA/bromwich_yoo_jc_2014.pdf (http://polarmet.osu.edu/ACCIMA/bromwich_yoo_jc_2014.pdf)
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: Shared Humanity on May 09, 2014, 04:33:57 PM
Hah! I've finally  found the proper home for this article which was just recently posted on ASIB.

http://www.dailykos.com/story/2014/03/05/1281907/-The-Antarctic-Half-of-the-Global-Thermohaline-Circulation-is-Collapsing (http://www.dailykos.com/story/2014/03/05/1281907/-The-Antarctic-Half-of-the-Global-Thermohaline-Circulation-is-Collapsing)

What are the implications?

Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: SteveMDFP on May 09, 2014, 07:29:10 PM
Hah! I've finally  found the proper home for this article which was just recently posted on ASIB.

http://www.dailykos.com/story/2014/03/05/1281907/-The-Antarctic-Half-of-the-Global-Thermohaline-Circulation-is-Collapsing (http://www.dailykos.com/story/2014/03/05/1281907/-The-Antarctic-Half-of-the-Global-Thermohaline-Circulation-is-Collapsing)

What are the implications?

Worse than either the author or comments there suggest.  The main mechanism of mass extinctions during the end-Permian event ("the great dying") was probably not heat itself, but collapse of oxygen delivery to the ocean floors, resulting in highly toxic hydrogen sulfide (H2S). 
Formation of deep water from cooled surface waters doesn't just distribute heat, it's the only major way for oxygen to get to the deep ocean waters.

Organic matter is taken up by organisms to grow.  Ordinarily, they use oxygen to react with carbon compounds to create the energy they need.  When the oxygen is used up, anaerobic bacteria will use dissolved sulfate, converting sulfate to hydrogen sulfide (the stuff with a rotten egg smell). 
H2S is highly toxic, it's been compared to cyanide gas.  Released at ocean depths it will simply kill all the ocean creatures we're familiar with.  When levels are high enough, it can be released into the atmosphere.
I think we're rapidly transitioning the globe to a Permian Extinction state.  Once started, that can continue, with positive feedback mechanisms, for many millenia to come.
We're already seeing more areas of ocean with hypoxic dead zones.  Expect to see more.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: sidd on May 10, 2014, 03:17:08 AM
Re: euxinic ocean

these papers by Kidder and Worsley are relevant

doi:10.1016/S0031-0182(03)00667-9

doi:10.1016/j.palaeo.2010.05.036

doi: 10.1130/G131A.1

the last at least is open access, and very good. There is another recent paper by (among others) Canfield, of Canfield ocean fame, but i do not immediately recall the reference.

I think you will find that widespread euxinia will take longer than centuries; however my guess is  acidic and possible euxinic conditions in the Red Sea or Mediterranean first.

sidd
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 10, 2014, 07:26:33 PM
Although this post could go into either the Paleo, or the Trends of the Southern Ocean, threads, I am putting it here because the paleo data presented in the linked reference (with a free access paper) represents a challenge of both Global and Regional Circulation Models related to the influence of the Southern Ocean during the Holocene (8,000 yrs age the mean global temperatures were a bit higher than now so calibrating the GCMs, & RCMs, to match the observed Holocene record should improve the model projections).  This challenge particularly focuses on the ventilation of the Northwest Pacific Ocean trigger by wind-driven changes in the Southern Ocean, as indicated by the title, abstract and attached image:

S. F. Rella    & M. Uchida, (2014),"A Southern Ocean trigger for Northwest Pacific ventilation during the Holocene?", Scientific Reports 4, Article number: 4046 doi:10.1038/srep0404

http://www.nature.com/srep/2014/140210/srep04046/full/srep04046.html?WT.ec_id=SREP-20140218 (http://www.nature.com/srep/2014/140210/srep04046/full/srep04046.html?WT.ec_id=SREP-20140218)

Abstract: "Holocene ocean circulation is poorly understood due to sparsity of dateable marine archives with submillennial-scale resolution. Here we present a record of mid-depth water radiocarbon contents in the Northwest (NW) Pacific Ocean over the last 12.000 years, which shows remarkable millennial-scale variations relative to changes in atmospheric radiocarbon inventory. Apparent decoupling of these variations from regional ventilation and mixing processes leads us to the suggestion that the mid-depth NW Pacific may have responded to changes in Southern Ocean overturning forced by latitudinal displacements of the southern westerly winds. By inference, a tendency of in-phase related North Atlantic and Southern Ocean overturning would argue against the development of a steady bipolar seesaw regime during the Holocene."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 30, 2014, 01:29:47 AM
The following abstract comes from the International Glacial Society Proceeding 65 at the following link:

http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm (http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm)

The Pollard and DeConto  2014 reference indicates that a new generation of Antarctic ice sheet modeling indicates that these ice sheets are less stable than previously expected:

70A0977
Modeling past and future ice retreat in Antarctic subglacial basins
David POLLARD, Robert DECONTO
Corresponding author: David Pollard
Corresponding author e-mail: pollard@essc.psu.edu

Abstract: "Geological data indicate that global mean sea level has fluctuated on O(104 to 105 year) timescales during the last ~25 million years. Peak levels are uncertain, but some estimated high stands are ~20 m or more above modern, for instance during the mid-Pliocene. If correct, this implies substantial variations in the size of the East Antarctic ice sheet (EAIS). However, climate and ice-sheet models have not been able to simulate significant EAIS retreat from continental size, given low proxy atmospheric CO2 levels during this time. Here, we use a continental Antarctic ice sheet model with two mechanisms based on previous studies and observations: (1) structural failure of large tidewater ice cliffs, and (2) enhanced ice-shelf calving due to meltwater drainage into crevasses. With climate forcing representing Pliocene warm periods, the two mechanisms accelerate West Antarctic collapse and produce retreat in major East Antarctic basins. Equivalent global mean sea-level rise is ~15 m, in better agreement with past sea-level data. The model is applied to specific past periods and to the long-term (100s to 1000s years) future, in which the ice sheet is found to be considerably more vulnerable to climate warming than previously modeled."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 30, 2014, 01:36:09 AM
The following abstract comes from the International Glacial Society Proceeding 65 at the following link:

http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm (http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm)

The Whitehouse et al 2014 reference indicates the importance and the challenges of including the impacts of relative sea-level changes on dynamic ice sheet models:

70A0997
Evaluating the impact of relative sea-level change on ice-sheet dynamics
Pippa WHITEHOUSE, Glenn MILNE, Andreas VIELI
Corresponding author: Pippa Whitehouse
Corresponding author e-mail: pippa.whitehouse@durham.ac.uk

Abstract: "The water depth of the surrounding ocean is a key factor in determining the dynamics of a marine-based ice sheet. In this study we outline two key ways in which sea-level changes impact ice-sheet dynamics, and we highlight potential errors that can be made if sea-level changes are not consistently modelled in parallel with the evolution of a marine-based ice sheet. Changes in relative sea level, i.e. water depth, will influence grounding line dynamics, both in terms of the location of the grounding line and the flux of ice across the grounding line. We explore the implications of considering realistic, spatially variable relative sea-level changes – derived using a glacial isostatic adjustment (GIA) model – as opposed to uniform, or ‘eustatic’, sea-level changes when determining the likely configuration of two key Antarctic outlet glaciers during the LGM. In particular, we highlight the different sea-level change experienced by East and West Antarctica due to rotational feedback. Secondly, changes in water depth will determine which portions of the ice sheet are grounded or floating. In the context of a GIA model, this information is needed to determine the magnitude of the ice and ocean load changes that are applied to the solid Earth. We demonstrate that if the evolving topography is incorrectly defined, particularly across ice-shelf regions, errors on the order of 10 mm a–1 can be made when predicting present-day uplift rates due to past ice mass changes. The correct modelling of water depth change is also necessary to study the evolution of ice rises, whose presence will impact the stress regime of an ice shelf and hence the dynamics of the upstream ice sheet, and to determine former ice-sheet thicknesses via the interpretation of iceberg scours."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on June 03, 2014, 05:51:39 AM
Hopefully, scientist can get their GCMs & RCMs to replicate the following paleo-evidence that the Southern Ocean can vent large amounts of  carbon dioxide back into the atmosphere during periods of global warming and of accelerating circumpolar Antarctic wind velocities (see the first post in this thread), discussed in the following linked reference:


Luke C. Skinner, Claire Waelbroeck, Adam E. Scrivner, and Stewart J. Fallon, (2014), "Radiocarbon evidence for alternating northern and southern sources of ventilation of the deep Atlantic carbon pool during the last deglaciation", PNAS, doi: 10.1073/pnas.1400668111, (March 31, 2014)



http://www.pnas.org/content/early/2014/03/27/1400668111.abstract (http://www.pnas.org/content/early/2014/03/27/1400668111.abstract)

Significance: "This study sheds light on the mechanisms of deglacial atmospheric CO2 rise and, more specifically, on the hypothesized role of a “bipolar seesaw” in deep Atlantic ventilation. Comparing new high-resolution radiocarbon reconstructions from the Northeast Atlantic with existing data from the Southern Ocean, we show that a bipolar ventilation seesaw did indeed operate during the last deglaciation. Whereas today the deep Atlantic’s carbon pool is “flushed” from the north by North Atlantic Deep Water export, it was flushed instead from the south during Heinrich Stadial 1 and the Younger Dryas, in time with sustained atmospheric CO2 rise."


Abstract: "Recent theories for glacial–interglacial climate transitions call on millennial climate perturbations that purged the deep sea of sequestered carbon dioxide via a “bipolar ventilation seesaw.” However, the viability of this hypothesis has been contested, and robust evidence in its support is lacking. Here we present a record of North Atlantic deep-water radiocarbon ventilation, which we compare with similar data from the Southern Ocean. A striking coherence in ventilation changes is found, with extremely high ventilation ages prevailing across the deep Atlantic during the last glacial period. The data also reveal two reversals in the ventilation gradient between the deep North Atlantic and Southern Ocean during Heinrich Stadial 1 and the Younger Dryas. These coincided with periods of sustained atmospheric CO2 rise and appear to have been driven by enhanced ocean–atmosphere exchange, primarily in the Southern Ocean. These results confirm the operation of a bipolar ventilation seesaw during deglaciation and underline the contribution of abrupt regional climate anomalies to longer-term global climate transitions."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on June 03, 2014, 11:54:38 PM
The linked research on the paleo- absorption of CO2 by the Southern Ocean (considering the influence of sea ice), represents another challenge for RCM hind-casts to match and calibrate to before projection future responses to AGW:

Raffaele Ferrari, Malte F. Janse, Jess F. Adkins, Andrea Burke, Andrew L. Stewart, and Andrew F. Thompson,  (2014), "Antarctic sea ice control on ocean circulation in present and glacial climates", Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.1323922111

http://www.pnas.org/content/early/2014/05/29/1323922111.abstract?sid=7f015fc3-4a3b-4d0a-8250-bfdce8fb1324 (http://www.pnas.org/content/early/2014/05/29/1323922111.abstract?sid=7f015fc3-4a3b-4d0a-8250-bfdce8fb1324)


Abstract: "In the modern climate, the ocean below 2 km is mainly filled by waters sinking into the abyss around Antarctica and in the North Atlantic. Paleoproxies indicate that waters of North Atlantic origin were instead absent below 2 km at the Last Glacial Maximum, resulting in an expansion of the volume occupied by Antarctic origin waters. In this study we show that this rearrangement of deep water masses is dynamically linked to the expansion of summer sea ice around Antarctica. A simple theory further suggests that these deep waters only came to the surface under sea ice, which insulated them from atmospheric forcing, and were weakly mixed with overlying waters, thus being able to store carbon for long times. This unappreciated link between the expansion of sea ice and the appearance of a voluminous and insulated water mass may help quantify the ocean’s role in regulating atmospheric carbon dioxide on glacial–interglacial timescales. Previous studies pointed to many independent changes in ocean physics to account for the observed swings in atmospheric carbon dioxide. Here it is shown that many of these changes are dynamically linked and therefore must co-occur."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on June 04, 2014, 12:31:03 AM
As we are beginning to enter mid-Pliocene type conditions, I provide the following link to the Zhang et al (2013) research (with a free access pdf) providing clear evidence that as the westerly (circumpolar) winds move poleward (towards the South Pole) as they currently are doing (due to the ozone hole and GHG increases), that the Southern Ocean vented large quantities of CO₂ into the mid-Pliocene atmosphere, less than 3 million years ago.  Hopefully, currently researchers can use such data to calibrate their RCM models, to see whether the Southern Ocean will soon vent large amounts of CO2 into the our modern atmosphere:

Zhongshi Zhang, Kerim H. Nisancioglu & Ulysses S. Ninnemann, (2013), "Increased ventilation of Antarctic deep water during the warm mid-Pliocene", Nature Communications, Volume: 4, Article number: 1499, doi:10.1038/ncomms2521


http://www.nature.com/ncomms/journal/v4/n2/full/ncomms2521.html (http://www.nature.com/ncomms/journal/v4/n2/full/ncomms2521.html)

Abstract: "The mid-Pliocene warm period is a recent warm geological period that shares similarities with predictions of future climate. It is generally held the mid-Pliocene Atlantic Meridional Overturning Circulation must have been stronger, to explain a weak Atlantic meridional δ13C gradient and large northern high-latitude warming. However, climate models do not simulate such stronger Atlantic Meridional Overturning Circulation, when forced with mid-Pliocene boundary conditions. Proxy reconstructions allow for an alternative scenario that the weak δ13C gradient can be explained by increased ventilation and reduced stratification in the Southern Ocean. Here this alternative scenario is supported by simulations with the Norwegian Earth System Model (NorESM-L), which simulate an intensified and slightly poleward shifted wind field off Antarctica, giving enhanced ventilation and reduced stratification in the Southern Ocean. Our findings challenge the prevailing theory and show how increased Southern Ocean ventilation can reconcile existing model-data discrepancies about Atlantic Meridional Overturning Circulation while explaining fundamental ocean features."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on July 07, 2014, 05:33:36 PM
The linked reference provides projections from a Global Circulation Model, GCM, that continued AGW will result in a rapid advection of warm ocean water exceeding 2 degrees C (up to 4 degrees C) into the 200-700m water depth (in the range of the bottom of the Antarctic ice shelves and adjoining grounding line) induced by weakened near-shore Ekman pumping, which is associated with weakened coastal currents.  While not unexpected, this is seriously bad news, and this indicates that the ASE glaciers may begin a rapid phase of collapse sooner, rather than latter:

Spence, P, S. Griffies, M. England, A. Hogg, O. Saenko, N. Jourdain, (2014), "Rapid subsurface warming and circulation changes of Antarctic coastal waters by poleward shifting winds", GRL; DOI: 10.1002/2014GL060613

http://onlinelibrary.wiley.com/doi/10.1002/2014GL060613/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2014GL060613/abstract)

Abstract: "The southern hemisphere westerly winds have been strengthening and shifting poleward since the 1950s. This wind trend is projected to persist under continued anthropogenic forcing, but the impact of the changing winds on Antarctic coastal heat distribution remains poorly understood. Here we show that a poleward wind shift at the latitudes of the Antarctic Peninsula can produce an intense warming of subsurface coastal waters that exceeds 2 °C at 200-700 m depth. The model simulated warming results from a rapid advective heat flux induced by weakened near-shore Ekman pumping, and is associated with weakened coastal currents. This analysis shows that anthropogenically induced wind changes can dramatically increase the temperature of ocean water at ice sheet grounding lines and at the base of floating ice shelves around Antarctica, with potentially significant ramifications for global sea level rise."

See also:

https://www.climatescience.org.au/content/751-changing-antarctic-winds-create-new-sea-level-threat (https://www.climatescience.org.au/content/751-changing-antarctic-winds-create-new-sea-level-threat)

See also:

http://www.sciencecodex.com/changing_antarctic_winds_create_new_sea_level_threat-136994 (http://www.sciencecodex.com/changing_antarctic_winds_create_new_sea_level_threat-136994)

Extract: "Changes to Antarctic winds have already been linked to southern Australia's drying climate but now it appears they may also have a profound impact on warming ocean temperatures under the ice shelves along the coastline of West and East Antarctic.
"When we included projected Antarctic wind shifts in a detailed global ocean model, we found water up to 4°C warmer than current temperatures rose up to meet the base of the Antarctic ice shelves," said lead author Dr Paul Spence from the ARC Centre of Excellence for Climate System Science (ARCCSS).
"The sub-surface warming revealed in this research is on average twice as large as previously estimated with almost all of coastal Antarctica affected. This relatively warm water provides a huge reservoir of melt potential right near the grounding lines of ice shelves around Antarctica. It could lead to a massive increase in the rate of ice sheet melt, with direct consequences for global sea level rise.""

See also:

http://www.laboratoryequipment.com/news/2014/07/changing-antarctic-winds-are-threat-sea-level (http://www.laboratoryequipment.com/news/2014/07/changing-antarctic-winds-are-threat-sea-level)
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on November 02, 2014, 02:14:28 AM
The following linked reference, and associated extracts, indicates that a new DoE (see also Replies #11, 12 & 13 regarding prior efforts from DoE labs) state-of-the-art Earth Systems Model, ESM, named Accelerated Climate Modeling for Energy (ACME), will include extensive sub-routines focused on the Antarctic Ice Sheet, AIS, (as well as the Greenland Ice Sheet, GIS) and possible abrupt SLR:

Bader D, W Collins, R Jacob, P Jones, P Rasch, M Taylor, P Thornton, and D Williams. "Accelerated Climate Modeling for Energy (ACME) Project Strategy and Initial Implementation Plan." 2014

http://climatemodeling.science.energy.gov/sites/default/files/publications/acme-project-strategy-plan_0.pdf (http://climatemodeling.science.energy.gov/sites/default/files/publications/acme-project-strategy-plan_0.pdf)

Extract: "2.2.1.3 Cryosphere System
Could a dynamical instability in the Antarctic Ice Sheet be triggered within the next 40 years?

The objective is to examine the near-term risk of initiating the dynamic instability and onset of the collapse of the Antarctic Ice Sheet due to rapid melting by warming waters adjacent to the ice-sheet grounding lines. The experiment would be the first fully coupled global simulation to include dynamic ice shelf–ocean interactions for addressing the potential instability associated with grounding line dynamics in marine ice sheets around Antarctica. It will utilize several significant advances in the new ACME model, including the ability to enhance spatial resolution in both the ice sheet and ocean model to resolve grounding-line processes while still maintaining global extent in a coupled system and throughput for decadal simulations. The simulation will include an eddy-resolving Southern Ocean as well to better represent Circumpolar Deep Water (CDW) and dynamics associated with bringing this water onto the continental shelf under the ice sheet. Including the sea-ice model captures the process of buttressing at the ice shelf–sea-ice boundary. Finally, a fully coupled system is able to simulate changes in atmospheric forcing (e.g., poleward displacement of jets) that could influence the behavior of the Southern Ocean and sea ice.
The specific experiment will be a fully coupled simulation from 1970–2050 to explore whether rapid ice-sheet instability is triggered in this time frame. An ensemble would be desirable to address the likelihood of such an event, though this is not likely to be affordable in our configuration in this timeframe. The model configuration for this experiment will be a modified version of the standard high-resolution ACME configuration described below. The base configuration includes the atmosphere/land on a 0.25° cubed-sphere grid using the ACME-modified CAM5-SE atmosphere model. The subgrid orography modifications will be needed to resolve Antarctic surface mass balance at the ice-sheet margins. The ocean component will be MPAS-O on a Spherical Centroidal Voronoi Tesselations (SCVT) mesh with 15-km grid spacing at the equator, decreasing to 5 km in the Southern Ocean region. The default mesh will be extended southward to include critical Antarctic embayments and the resolution in these regions will be further enhanced if affordable. The vertical grid will be a hybrid coordinate with 100 vertical levels. The sea-ice component will be MPAS-CICE on the same ocean grid. Finally, we will add an Antarctic Ice Sheet model with resolution of 0.5–1 km near likely grounding-line locations and coarser resolution (~10 km) throughout the interior. For initial conditions, we will follow a similar spin-up procedure as with previous high-resolution simulations, with an ocean/ice state from an ocean/ice reanalysis-forced spin-up. For the ice sheet, an optimized initial condition should be available from the PISCEES project.
This first-of-its-kind coupled simulation will be focused largely on the ocean–ice shelf feedbacks and potential for dynamical instability and rapid SLR. It represents a first step toward a comprehensive SLR and impacts capability needed by the DOE to assess threats to coastal facilities. As work proceeds toward the more comprehensive experiments planned in the 10-year timeframe, we will be incrementally adding additional features. For example, work will begin under this project to develop an initial implementation of icebergs and primitive calving laws to capture the transport and distribution of ice and other material as the ice sheets flow into the ocean. Work also continues (as part of related projects) on a Greenland Ice Sheet model so that we can capture SLR contributions from both major ice sheets. We will also begin to include isostasy and ice-sheet self-gravity that can have a first-order effect on the regional SLR signature around the coastal U.S. We anticipate all of these effects to be included in a following ACME version. Further releases will begin to include wave models, further focusing of resolution in coastal and storm-track regions, and other capabilities needed to further refine SLR impact at regional scales.

2.2.2.3 Cryosphere System
How will regional variations in sea level rise interact with more extreme storms to enhance the coastal impacts of SLR?
The aim of this simulation is to determine the potential impacts on the nation’s coastal zones due to SLR exacerbated by regional variations in SLR and extreme storm surges. The novel aspects of this simulation are:
1. Fully coupled models of the cryosphere, including both major land ice sheets, the floating ice shelves surrounding Antarctica, the interactions with surrounding sea ice, and icebergs calved from Antarctica and Greenland
2. Complete treatments of the impacts of time-evolving isostasy and ice-sheet self-gravity on SLR
3. Addition of wave models to the ocean component
4. Deployment of enhanced resolution in all components to resolve dynamics at ice-sheet margins, sea-ice behavior, and the effects of severe weather on sea state in the major storm tracks

This experiment is based upon DOE’s advances in dynamic and adaptive ice-sheet modeling combined with the capacity for ultrahigh resolution of the land ice sheets and surrounding oceans using upcoming advances toward extreme-scale computing.

4.4 Ice Sheets
The ice-sheet model brings in a new set of interactions that must be understood and monitored for development or reduction of biases. The state of the atmosphere is essential to the surface mass balance, which in turn must be compared against other mass loss terms (iceberg calving, submarine melting). Along with monitoring of changes in grounded ice area and volume and these related mass balance terms, some of which may prove useful as metrics in a coupled context, a research problem we intend to take on is the development of Circumpolar Deep Water (CDW) metrics. Where waters are all near freezing, the relatively warm CDW, often found below colder and fresher waters, has a strong potential to accelerate submarine melting and therefore to strongly impact the overall mass balance of the Antarctic Ice Sheet. Stronger winds can drive greater upwelling and bring these warm waters in contact with the ice shelf. Research to understand the controls on CDW state and variability will be undertaken, facilitating the establishment of metrics focused on CDW mean state and variability, ensuring that transitions to or from rapid submarine melt states are not modeling artifacts but are robust and well understood. This effort will be critical for successfully answering the cryospheric driving question."

See also:
http://www.forbes.com/sites/jamesconca/2014/10/13/the-great-climate-model/ (http://www.forbes.com/sites/jamesconca/2014/10/13/the-great-climate-model/)

Extract: "We need a Great Climate Model.

The national laboratories of the Department of Energy are working on just such a model. Teamed with the National Center for Atmospheric Research, four academic institutions and one private company to form the Accelerated Climate Modeling for Energy, or ACME project, the national labs will help develop the most complete, fully coupled, state-of-the-science Earth system model to date.

Pacific Northwest National Laboratory (PNNL), Argonne, Brookhaven, Lawrence Berkeley, Lawrence Livermore, Los Alamos, Oak Ridge and Sandia will conduct simulations and modeling on the highest performance computing systems in the world. That includes over a hundred petaflop machines and the soon-to-be-operational exascale supercomputers."

&

http://www.scientificcomputing.com/news/2014/09/developing-most-advanced-earth-system-computer-model-yet-created (http://www.scientificcomputing.com/news/2014/09/developing-most-advanced-earth-system-computer-model-yet-created)

Extract: "LOS ALAMOS, NM — With President Obama announcing climate-support initiatives at the 2014 United Nations Climate Summit, the U.S. Department of Energy national laboratories are teaming with academia and the private sector to develop the most advanced climate and Earth system computer model yet created. For Los Alamos National Laboratory researchers, it is a welcome advance for an already vibrant high-performance computing community.
Accelerated Climate Modeling for Energy, or ACME, is designed to accelerate the development and application of fully coupled, state-of-the-science Earth system models for scientific and energy applications."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: steve s on November 02, 2014, 07:47:56 AM
The effort is so hopeful, and if it could be pulled off it would very useful. Seems like a difficult or even impossible model to debug, though. If debugged, an incredibly difficult model to fit with accurate parameters. Many statistical difficulties would have to be ignored, any of which could throw off results.

I hope that it points the way to better back-of-the-napkin thinking by showing critical bottlenecks.   

(I'm not picking on this effort, for it is impossible to test the computational validity/accuracy of large complex computer solutions under the theoretically simplest scenarios -- and this is not simple.)
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on November 10, 2014, 11:14:44 PM
The following reference shows a large-scale climate response to a retreat of the WAIS, including associated feedbacks in the oceanic and atmospheric circulation patterns:

F. Justino, A. S. Silva, M. P. Pereira, F. Stordal, D. Lindemann and F. Kucharski, (2014), "The large-scale climate in response to the retreat of the West Antarctic Ice Sheet", Journal of Climate; doi: http://dx.doi.org/10.1175/JCLI-D-14-00284.1 (http://dx.doi.org/10.1175/JCLI-D-14-00284.1)

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00284.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00284.1)

Abstract: "Based upon coupled climate simulations driven by present day and conditions resembling the Marine Isotope Stage 31 (WICE-EXP), insofar the West Antarctic Ice Sheet (WAIS) configuration is concerned, we demonstrate that changes in the WAIS orography lead to noticiable changes in the oceanic and atmospheric circulations. Compared with the present day climate, the WICE-EXP is characterized by warmer conditions in the Southern Hemisphere (SH) by up to 5°C in the polar oceans and up to 2°C in the Northern Hemisphere (NH). These changes feed back on the atmospheric circulation weakening (strengthening) the extratropical westerlies in the SH (northern Atlantic). Calculations of the Southern Annular Mode (SAM) show that modification of the WAIS induces warmer conditions and a northward shift of the westerly flow, in particular there is a clear weakening of the polar jet. These changes lead to modification of the rate of deep water formation reducing the magnitude of the North Atlantic Deep Water, but enhancing the Antarctic Bottom Water. By evaluating the density flux we have found that the thermal density flux has played a main role in the modification of the meridional overturning circulation. Moreover, the climate anomalies between the WICE-EXP and the present day simulations resemble a bipolar seesaw pattern. These results are in good agreement with paleorecontructions in the framework of the Ocean Drilling and ANDRILL Programs."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on November 17, 2014, 11:38:07 PM
The linked reference (with an open access pdf) indicates that two coupled climate models show that in response to an ozone depletion the Southern Ocean responded with two processes for sea ice extent change.  The first process based on a northward Ekman drift occurred relatively quickly and served to expand Antarctic sea ice extent about three decades ago.  The second process acted relatively more slowly (years to decades), results in a warming trend for the Southern Ocean leading to a reduction in projected sea ice extent (see attached figure).  Based on these findings we can expect Antarctic amplification to begin accelerating in the next decade or so.

David Ferreira, John Marshall, Cecilia M. Bitz, Susan Solomon, and Alan Plumb, (2014) "Antarctic ocean and sea ice response to ozone depletion: a two timescale problem", Journal of Climate, In press.

http://www.met.rdg.ac.uk/~gf905417/Publications_files/Twotimescale_final.pdf (http://www.met.rdg.ac.uk/~gf905417/Publications_files/Twotimescale_final.pdf)


Abstract: "The response of the Southern Ocean to a repeating seasonal cycle of ozone loss is studied in two coupled climate models and found to comprise both fast and slow processes. The fast response is similar to the inter-annual signature of the Southern Annular Mode (SAM) on Sea Surface Temperature (SST), on to which the ozone-hole forcing projects in the summer. It comprises enhanced northward Ekman drift inducing negative summertime SST anomalies around Antarctica, earlier sea ice freeze-up the following winter, and northward expansion of the sea ice edge year-round. The enhanced northward Ekman drift, however, results in upwelling of warm waters from below the mixed layer in the region of seasonal sea ice. With sustained bursts of westerly winds induced by ozone-hole depletion, this warming from below eventually dominates over the cooling from anomalous Ekman drift. The resulting slow-timescale response (years to decades) leads to warming of SSTs around Antarctica and ultimately a reduction in sea-ice cover year-round. This two-timescale behavior – rapid cooling followed by slow but persistent warming - is found in the two coupled models analysed, one with an idealized geometry, the other a complex global climate model with realistic geometry. Processes that control the timescale of the transition from cooling to warming, and their uncertainties are described. Finally we discuss the implications of our results for rationalizing previous studies of the effect of the ozone-hole on SST and sea-ice extent."

Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: sidd on November 18, 2014, 01:02:05 AM
That Ferreira paper is interesting. Forcing that analysis with the observed freshening signal in the southern ocean might actually yield good regional level results.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on January 19, 2015, 08:11:26 PM
The linked research indicates that thermodynamics (warming and near-surface stability) control 21st century Southern Ocean shortwave climate feedbacks.  Besides illustrating how challenging it is to correctly model the Antarctic region, this research indicates to me that if the telecommunication of Pacific Tropical energy to the WAIS occurs (as many models project), then the West Antarctic could be subject to more positive feedback (warming) in the 21st century than previous assumed in the AR5 models.

Kay, J. E., B. Medeiros, Y.-T. Hwang, A. Gettelman, J. Perket, and M. G. Flanner (2014), Processes controlling Southern Ocean shortwave climate feedbacks in CESM, Geophys. Res. Lett., 41, 616–622, doi:10.1002/2013GL058315.

http://onlinelibrary.wiley.com/doi/10.1002/2013GL058315/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2013GL058315/abstract)

Abstract: "A climate model (Community Earth System Model with the Community Atmosphere Model version 5 (CESM-CAM5)) is used to identify processes controlling Southern Ocean (30–70°S) absorbed shortwave radiation (ASR). In response to 21st century Representative Concentration Pathway 8.5 forcing, both sea ice loss (2.6 W m−2) and cloud changes (1.2 W m−2) enhance ASR, but their relative importance depends on location and season. Poleward of ~55°S, surface albedo reductions and increased cloud liquid water content (LWC) have competing effects on ASR changes. Equatorward of ~55°S, decreased LWC enhances ASR. The 21st century cloud LWC changes result from warming and near-surface stability changes but appear unrelated to a small (1°) poleward shift in the eddy-driven jet. In fact, the 21st century ASR changes are 5 times greater than ASR changes resulting from large (5°) naturally occurring jet latitude variability. More broadly, these results suggest that thermodynamics (warming and near-surface stability), not poleward jet shifts, control 21st century Southern Ocean shortwave climate feedbacks."

Also see:
http://cires.colorado.edu/science/groups/kay/Publications/ (http://cires.colorado.edu/science/groups/kay/Publications/)
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on January 21, 2015, 01:38:37 AM
The linked reference indicates that improved modeling of external freshwater flux (from ice melting) significantly improved the accuracy of the Earth System Models of the High-Latitude Southern Ocean region:

Achim Stössel, Dirk Notz, F. Alexander Haumann, Helmuth Haak, Johann Jungclaus & Uwe Mikolajewicz, (2015), "Controlling high-latitude Southern Ocean convection in climate models", Ocean Modelling, Volume 86, February 2015, Pages 58–75, doi:10.1016/j.ocemod.2014.11.008


http://www.sciencedirect.com/science/article/pii/S1463500314001760 (http://www.sciencedirect.com/science/article/pii/S1463500314001760)


Abstract: "Earth System Models (ESMs) generally suffer from a poor simulation of the High-Latitude Southern Ocean (HLSO). Here we aim at a better understanding of the shortcomings by investigating the sensitivity of the HLSO to the external freshwater flux and the horizontal resolution in forced and coupled simulations with the Max-Planck-Institute Ocean Model (MPIOM). Forced experiments reveal an immediate reduction of open-ocean convection with additional freshwater input. The latter leads to a remarkably realistic simulation of the distinct water-mass structure in the central Weddell Sea featuring a temperature maximum of +0.5 °C at 250 m depth. Similar, but more modest improvements occur over a time span of 40 years after switching from a forced to a coupled simulation with an eddy-resolving version of MPIOM. The switch is accompanied with pronounced changes of the external freshwater flux and the wind field, as well as a more realistic heat flux due to coupling. Similar to the forced freshwater-flux experiments, a heat reservoir develops at depth, which in turn decreases the vertically integrated density of the HLSO and reduces the Antarctic Circumpolar Current to rather realistic values. Coupling with a higher resolution version of the atmosphere model (ECHAM6) yields distinct improvements of the HLSO water-mass structure and sea-ice cover. While the coupled simulations reveal a realistic amount of Antarctic runoff, its distribution appears too concentrated along the coast. Spreading the runoff over a wider region, as suggested in earlier studies to mimic the effect of freshwater transport through icebergs, also leads to noticeable improvements of the HLSO water-mass properties, predominantly along the coast. This suggests that the spread of the runoff improves the representation of Antarctic Bottom Water formation through enhanced near-boundary convection rather than weakened open-ocean convection."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on January 22, 2015, 04:32:56 PM
The authors of the linked reference about atmospheric river events in Antarctica found that:

(a) The nine atmospheric rivers that hit East Antarctica between 2009 and 2011 accounted for 80 per cent of the exceptional snow accumulation at Princess Elisabeth station; and
(b) "The unusually high snow accumulation in Dronning Maud Land in 2009 that we attributed to atmospheric rivers added around 200 gigatons of mass to Antarctica, which alone offset 15 per cent of the recent 20-year ice sheet mass loss," see the attach image and associated caption below.

I would like to point-out:
 
(a) First, that atmospheric river events have been historically rare and to have nine such events hit Dronning Maud Land between 2009 and 2011 indicates that extreme weather is becoming more common in the Southern Ocean; and
(b) Second, as global warming continues future atmospheric events may more frequenctly drop rain instead of snow on Antarctica; which would be a positive feedback for ice mass loss & SLR:

Also, I would like to point-out that modeling such future atmospheric river events represents a significant challenge for regional modelers to get right:

Gorodetskaya, I. V., M. Tsukernik, K. Claes, M. F. Ralph, W. D. Neff, and N. P. M. Van Lipzig, (2014), "The role of atmospheric rivers in anomalous snow accumulation in East Antarctica", Geophys. Res. Lett., 41, 6199–6206, doi:10.1002/2014GL060881.


http://onlinelibrary.wiley.com/doi/10.1002/2014GL060881/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2014GL060881/abstract)

Abstract: "Recent, heavy snow accumulation events over Dronning Maud Land (DML), East Antarctica, contributed significantly to the Antarctic ice sheet surface mass balance (SMB). Here we combine in situ accumulation measurements and radar-derived snowfall rates from Princess Elisabeth station (PE), located in the DML escarpment zone, along with the European Centre for Medium-range Weather Forecasts Interim reanalysis to investigate moisture transport patterns responsible for these events. In particular, two high-accumulation events in May 2009 and February 2011 showed an atmospheric river (AR) signature with enhanced integrated water vapor (IWV), concentrated in narrow long bands stretching from subtropical latitudes to the East Antarctic coast. Adapting IWV-based AR threshold criteria for Antarctica (by accounting for the much colder and drier environment), we find that it was four and five ARs reaching the coastal DML that contributed 74–80% of the outstanding SMB during 2009 and 2011 at PE. Therefore, accounting for ARs is crucial for understanding East Antarctic SMB."

Caption: "A meteorological image of an atmospheric river slamming into the East Antarctic coast on 15 February 2011. L indicates the atmospheric river's low-pressure trough and H indicates the blocking high-pressure ridge further downstream, directing moisture transport (red arrows) into the Dronning Maud Land and the Princess Elisabeth base (white square). The colours show total moisture amounts (in centimetres equivalent of water). Credit: Irina Gorodetskaya"


See also:
http://www.spacedaily.com/reports/Giant_atmospheric_rivers_add_mass_to_Antarcticas_ice_sheet_999.html (http://www.spacedaily.com/reports/Giant_atmospheric_rivers_add_mass_to_Antarcticas_ice_sheet_999.html)

http://phys.org/news/2015-01-giant-atmospheric-rivers-mass-antarctica.html (http://phys.org/news/2015-01-giant-atmospheric-rivers-mass-antarctica.html)
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on March 13, 2015, 10:22:37 PM
The linked reference (with an open access pdf) shows how basal ice-shelf channels in Antarctic ice shelves imprint the ice flowfield with enhanced horizontal shearing across the channels.  This presents the possibility of identifying and classifying such channels from satellite observations; which would be an important step in incorporating the effects of these channels in ice-ocean models for Antarctic ice shelves.

Drews, R. (2015), "Evolution of ice-shelf channels in Antarctic ice shelves", The Cryosphere Discuss., 9, 1603-1631, doi:10.5194/tcd-9-1603-2015

http://www.the-cryosphere-discuss.net/9/1603/2015/tcd-9-1603-2015.html (http://www.the-cryosphere-discuss.net/9/1603/2015/tcd-9-1603-2015.html)

Abstract: "Ice shelves buttress the continental ice flux and mediate ice–ocean interactions. They are often traversed by channels in which basal melting is enhanced, impacting ice-shelf stability. Here, channel evolution is investigated using a transient, three-dimensional full Stokes model and geophysical data collected on Roi Baudouin Ice Shelf (RBIS), Antarctica. The modeling confirms basal melting as a feasible mechanism for channel creation, although channels may also advect without melting for many tens of kilometers. Channels can be out of hydrostatic equilibrium depending on their width and the upstream melt history. Inverting surface elevation for ice thickness in those areas is erroneous and corresponding observational evidence is presented at RBIS by comparing the hydrostatically inverted ice thickness with radar measurements. The model shows that channelized melting imprints the flowfield characteristically, which can result in enhanced horizontal shearing across channels. This is exemplified for a channel at RBIS using observed surface velocities and opens up the possibility to classify channelized melting from space, an important step towards incorporating these effects in ice–ocean models."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on March 19, 2015, 12:05:32 AM
If you click on the pdf links before the end of March 2015 you can down load pdfs of all of these 2014 Phil. Trans. papers on the Southern Ocean.

Andrew J. Watson, Michael P. Meredith, John Marshall (2014), "The Southern Ocean, carbon and climate", Phil Trans R Soc A., 372 2019 20130057; doi: 10.1098/rsta.2013.0057

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130057.full.pdf (http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130057.full.pdf)


Marshall J, Armour KC, Scott, JR, Kostov Y, Hausmann U, Ferreira D, Shepherd, TG, Bitz CM. (2014) "The ocean’s role in polar climate change: asymmetric Arctic and Antarctic responses to greenhouse gas and ozone forcing". Phil. Trans. R. Soc. A 372: 20130040. http://dx.doi.org/10.1098/rsta.2013.0040 (http://dx.doi.org/10.1098/rsta.2013.0040)

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130040.full.pdf (http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130040.full.pdf)

Meijers AJS. (2014), "The Southern Ocean in the Coupled Model Intercomparison Project phase 5". Phil. Trans. R. Soc. A 372: 20130296. http://dx.doi.org/10.1098/rsta.2013.0296 (http://dx.doi.org/10.1098/rsta.2013.0296)

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130296.full.pdf (http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130296.full.pdf)

http://rsta.royalsocietypublishing.org/content/372/2019/20130296 (http://rsta.royalsocietypublishing.org/content/372/2019/20130296)


Heywood KJ et al. (2014) "Ocean processes at the Antarctic continental slope". Phil. Trans. R. Soc. A 372: 20130047. http://dx.doi.org/10.1098/rsta.2013.0047 (http://dx.doi.org/10.1098/rsta.2013.0047)

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130047.full.pdf (http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130047.full.pdf)

http://rsta.royalsocietypublishing.org/content/372/2019/20130047 (http://rsta.royalsocietypublishing.org/content/372/2019/20130047)



Gille ST. (2014) "Meridional displacement of the Antarctic Circumpolar Current". Phil. Trans. R. Soc. A 372: 20130273.
http://dx.doi.org/10.1098/rsta.2013.0273 (http://dx.doi.org/10.1098/rsta.2013.0273)

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130273.full.pdf (http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130273.full.pdf)

http://rsta.royalsocietypublishing.org/content/372/2019/20130273 (http://rsta.royalsocietypublishing.org/content/372/2019/20130273)

Meredith MP, Jullion L, Brown PJ, Naveira Garabato AC, Couldrey MP. (2014), "Dense waters of theWeddell and Scotia Seas: recent changes in properties and circulation". Phil. Trans. R. Soc. A 372: 20130041. http://dx.doi.org/10.1098/rsta.2013.0041 (http://dx.doi.org/10.1098/rsta.2013.0041)

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130041.full.pdf (http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130041.full.pdf)

http://rsta.royalsocietypublishing.org/content/372/2019/20130041 (http://rsta.royalsocietypublishing.org/content/372/2019/20130041)

Abstract: " The densest waters in the Atlantic overturning circulation are sourced at the periphery of Antarctica, especially the Weddell Sea, and flow northward via routes that involve crossing the complex bathymetry of the Scotia Arc. Recent observations of significant warming of these waters along much of the length of the Atlantic have highlighted the need to identify and understand the time-varying formation and export processes, and the controls on their properties and flows. Here, we review recent developments in understanding of the processes that control the changing flux of water through the main export route from the Weddell Sea into the Scotia Sea, and the transformations of the waters within the Scotia Sea and environs. We also present a synopsis of recent findings that relate to the climatic change of dense water properties within the Weddell Sea itself, in the context of known Atlantic-scale changes. Among the most significant findings are the discovery that the warming of waters exported from the Weddell Sea has been accompanied by a significant freshening, and that the episodic nature of the overflow into the Scotia Sea is markedly wind-controlled and can lead to significantly enhanced abyssal stratification. Key areas for focusing future research effort are outlined."

Brown PJ, Meredith MP, Jullion L, Naveira Garabato A, Torres-Valdés S, Holland P, Leng MJ, Venables H. 2014 Freshwater fluxes in theWeddell Gyre: results from δ18O. Phil. Trans. R. Soc. A 372: 20130298. http://dx.doi.org/10.1098/rsta.2013.0298 (http://dx.doi.org/10.1098/rsta.2013.0298)

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130298.full.pdf (http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130298.full.pdf)

http://rsta.royalsocietypublishing.org/content/372/2019/20130298 (http://rsta.royalsocietypublishing.org/content/372/2019/20130298)

Abstract: "Full-depth measurements of δ18O from 2008 to 2010 enclosing the Weddell Gyre in the Southern Ocean are used to investigate the regional freshwater budget. Using complementary salinity, nutrients and oxygen data, a four-component mass balance was applied to quantify the relative contributions of meteoric water (precipitation/glacial input), sea-ice melt and saline (oceanic) sources. Combination of freshwater fractions with velocity fields derived from a box inverse analysis enabled the estimation of gyre-scale budgets of both freshwater types, with deep water exports found to dominate the budget. Surface net sea-ice melt and meteoric contributions reach 1.8% and 3.2%, respectively, influenced by the summer sampling period, and −1.7% and +1.7% at depth, indicative of a dominance of sea-ice production over melt and a sizable contribution of shelf waters to deep water mass formation. A net meteoric water export of approximately 37 mSv is determined, commensurate with local estimates of ice sheet outflow and precipitation, and the Weddell Gyre is estimated to be a region of net sea-ice production. These results constitute the first synoptic benchmarking of sea-ice and meteoric exports from the Weddell Gyre, against which future change associated with an accelerating hydrological cycle, ocean climate change and evolving Antarctic glacial mass balance can be determined."

Hogg AMcC, Munday DR. (2014), "Does the sensitivity of Southern Ocean circulation depend upon bathymetric details?", Phil. Trans. R. Soc. A 372: 20130050. http://dx.doi.org/10.1098/rsta.2013.0050 (http://dx.doi.org/10.1098/rsta.2013.0050)

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130050.full.pdf (http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130050.full.pdf)

http://rsta.royalsocietypublishing.org/content/372/2019/20130050 (http://rsta.royalsocietypublishing.org/content/372/2019/20130050)

Abstract: "The response of the major ocean currents to changes in wind stress forcing is investigated with a series of idealized, but eddy-permitting, model simulations. Previously, ostensibly similar models have shown considerable variation in the oceanic response to changing wind stress forcing. Here, it is shown that a major reason for these differences in model sensitivity is subtle modification of the idealized bathymetry. The key bathymetric parameter is the extent to which the strong eddy field generated in the circumpolar current can interact with the bottom water formation process. The addition of an embayment, which insulates bottom water formation from meridional eddy fluxes, acts to stabilize the deep ocean density and enhances the sensitivity of the circumpolar current. The degree of interaction between Southern Ocean eddies and Antarctic shelf processes may thereby control the sensitivity of the Southern Ocean to change."

Waugh DW (2014), "Changes in the ventilation of the southern oceans", Phil. Trans. R. Soc. A 372, 20130269. DOI: 10.1098/rsta.2013.0269

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130269.full.pdf (http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130269.full.pdf)

http://rsta.royalsocietypublishing.org/content/372/2019/20130269 (http://rsta.royalsocietypublishing.org/content/372/2019/20130269)

Abstract: "Changes in the ventilation of the southern oceans over the past few decades are examined using ocean measurements of CFC-12 and model simulations. Analysis of CFC-12 measurements made between the late 1980s and late 2000s reveal large-scale coherent changes in the ventilation, with a decrease in the age of subtropical Subantarctic Mode Waters (SAMW) and an increase in the age of Circumpolar Deep Waters. The decrease in SAMW age is consistent with the observed increase in wind stress curl and strength of the subtropical gyres over the same period. A decrease in the age of SAMW is also found in Community Climate System Model version 4 perturbation experiments where the zonal wind stress is increased. This decrease is due to both more rapid transport along isopycnals and the movement of the isopycnals. These results indicate that the intensification of surface winds in the Southern Hemisphere has caused large-scale coherent changes in the ventilation of the southern oceans."


van Heuven SMAC, Hoppema M, Jones EM, de Baar HJW. (2014), "Rapid invasion of anthropogenic CO2 into the deep circulation of the Weddell Gyre". Phil. Trans. R. Soc. A 372: 20130056. http://dx.doi.org/10.1098/rsta.2013.0056 (http://dx.doi.org/10.1098/rsta.2013.0056)

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130056.full.pdf (http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130056.full.pdf)

http://rsta.royalsocietypublishing.org/content/372/2019/20130056 (http://rsta.royalsocietypublishing.org/content/372/2019/20130056)

Abstract: "Data are presented for total carbon dioxide (TCO2), oxygen and nutrients from 14 cruises covering two repeat sections across the Weddell Gyre, from 1973 to 2010. Assessments of the rate of increase in anthropogenic CO2 (Cant) are made at three locations. Along the Prime Meridian, TCO2 is observed to steadily increase in the bottom water. Accompanying changes in silicate, nitrate and oxygen confirm the non-steady state of the Weddell circulation. The rate of increase in TCO2 of +0.12±0.05 μmol kg−1 yr−1 therefore poses an upper limit to the rate of increase in Cant. By contrast, the bottom water located in the central Weddell Sea exhibits no significant increase in TCO2, suggesting that this water is less well ventilated at the southern margins of the Weddell Sea. At the tip of the Antarctic Peninsula (i.e. the formation region of the bottom water found at the Prime Meridian), the high rate of increase in TCO2 over time observed at the lowest temperatures suggests that nearly full equilibration occurs with the anthropogenic CO2 of the atmosphere. This observation constitutes rare evidence for the possibility that ice cover is not a major impediment for uptake of Cant in this prominent deep water formation region."


Majkut JD, Carter BR, Frölicher TL, Dufour CO, Rodgers KB, Sarmiento JL. (2014), "An observing system simulation for Southern Ocean carbon dioxide uptake". Phil. Trans. R. Soc. A 372: 20130046. http://dx.doi.org/10.1098/rsta.2013.0046 (http://dx.doi.org/10.1098/rsta.2013.0046)

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130046.full.pdf (http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130046.full.pdf)

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130046.full.pdf (http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130046.full.pdf)

Abstract: "The Southern Ocean is critically important to the oceanic uptake of anthropogenic CO2. Up to half of the excess CO2 currently in the ocean entered through the Southern Ocean. That uptake helps to maintain the global carbon balance and buffers transient climate change from fossil fuel emissions. However, the future evolution of the uptake is uncertain, because our understanding of the dynamics that govern the Southern Ocean CO2 uptake is incomplete. Sparse observations and incomplete model formulations limit our ability to constrain the monthly and annual uptake, interannual variability and long-term trends. Float-based sampling of ocean biogeochemistry provides an opportunity for transforming our understanding of the Southern Ocean CO2 flux. In this work, we review current estimates of the CO2 uptake in the Southern Ocean and projections of its response to climate change. We then show, via an observational system simulation experiment, that float-based sampling provides a significant opportunity for measuring the mean fluxes and monitoring the mean uptake over decadal scales."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: jai mitchell on March 19, 2015, 06:25:05 AM
The following link leads to a nice summary (from October 2013) of the ARGO findings through the end of 2012:

http://ceres.larc.nasa.gov/documents/STM/2013-10/14_Global_averages.pdf (http://ceres.larc.nasa.gov/documents/STM/2013-10/14_Global_averages.pdf)

As indicated in the attached figure, one key finding is that all of the ocean heat gain in the ARGO era has been in the Southern Hemisphere (which indicates that all of the steric SLR in in the ARGO era has been in the Southern Hemisphere).  This provides additional support to my position that when the current EL Nino hiatus period ends, there is an excess of heat in the Southern Ocean that can accelerate ice mass loss from Antarctica once the local winds/current shift sufficiently to increase the ocean interaction with the grounded ice.

This seems to confirm to me my suspicion re: NH aerosol loading and the implications of Durack et. al (2014)  back of the napkin calculation lends itself to .5-.7 watts per meter squared negative aerosol loading in the northern hemisphere, though this feels low to me.

ahh yes, that would be the average value from 2007. . .ok that makes sense.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on March 30, 2015, 05:10:50 AM
As one of the three stated goals that ACME focuses on is improved projections for the cryosphere, I decided to post the following references funded by the ACME program here:


Storer, R. L., Griffin, B. M., Höft, J., Weber, J. K., Raut, E., Larson, V. E., Wang, M., and Rasch, P. J. (2015), "Parameterizing deep convection using the assumed probability density function method", Geosci. Model Dev., 8, 1-19, doi:10.5194/gmd-8-1-2015


http://www.geosci-model-dev.net/8/1/2015/gmd-8-1-2015.html (http://www.geosci-model-dev.net/8/1/2015/gmd-8-1-2015.html)


Abstract: "Due to their coarse horizontal resolution, present day climate models must parameterize deep convection. This paper presents single-column simulations of deep convection using a probability density function (PDF) parameterization. The PDF parameterization predicts the PDF of subgrid variability of turbulence, clouds, and hydrometeors. That variability is interfaced to a prognostic microphysics scheme using a Monte Carlo sampling method.
The PDF parameterization is used to simulate tropical deep convection, the transition from shallow to deep convection over land, and midlatitude deep convection. These parameterized single-column simulations are compared with 3-D reference simulations. The agreement is satisfactory except when the convective forcing is weak.

The same PDF parameterization is also used to simulate shallow cumulus and stratocumulus layers. The PDF method is sufficiently general to adequately simulate these five deep, shallow, and stratiform cloud cases with a single equation set. This raises hopes that it may be possible in the future, with further refinements at coarse time step and grid spacing, to parameterize all cloud types in a large-scale model in a unified way."

Le Page Y, Morton D, Bond-Lamberty B, J Pereira MC, Hurtt G. (2015), "HESFIRE: A Global Fire Model to Explore the Role of Anthropogenic and Weather Drivers", Biogeosciences;12:887-903, doi:10.5194/bg-12-887-2015


http://www.biogeosciences.net/12/887/2015/bg-12-887-2015.html (http://www.biogeosciences.net/12/887/2015/bg-12-887-2015.html)


Abstract. Vegetation fires are a major driver of ecosystem dynamics and greenhouse gas emissions. Anticipating potential changes in fire activity and their impacts relies first on a realistic model of fire activity (e.g., fire incidence and interannual variability) and second on a model accounting for fire impacts (e.g., mortality and emissions). In this paper, we focus on our understanding of fire activity and describe a new fire model, HESFIRE (Human–Earth System FIRE), which integrates the influence of weather, vegetation characteristics, and human activities on fires in a stand-alone framework. It was developed with a particular emphasis on allowing fires to spread over consecutive days given their major contribution to burned areas in many ecosystems. A subset of the model parameters was calibrated through an optimization procedure using observation data to enhance our knowledge of regional drivers of fire activity and improve the performance of the model on a global scale. Modeled fire activity showed reasonable agreement with observations of burned area, fire seasonality, and interannual variability in many regions, including for spatial and temporal domains not included in the optimization procedure. Significant discrepancies are investigated, most notably regarding fires in boreal regions and in xeric ecosystems and also fire size distribution. The sensitivity of fire activity to model parameters is analyzed to explore the dominance of specific drivers across regions and ecosystems. The characteristics of HESFIRE and the outcome of its evaluation provide insights into the influence of anthropogenic activities and weather, and their interactions, on fire activity.


See also:
http://news.sciencemag.org/climate/2014/12/new-u-s-climate-model-project-getting-cautious-praise (http://news.sciencemag.org/climate/2014/12/new-u-s-climate-model-project-getting-cautious-praise)
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on March 31, 2015, 01:29:39 AM
The linked website contains numerous presentations related to Earth Systems Modeling from a May 2014 meeting associated with the ACME program:

http://climatemodeling.science.energy.gov/presentations/2014 (http://climatemodeling.science.energy.gov/presentations/2014)
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on April 05, 2015, 02:27:01 AM
Oceanic gravity wave can have a significant impact on the rate of calving from ice shelves (which is important to the stability of Antarctic marine glaciers), and the linked reference provide new insights into efforts to improve the accuracy of climate models (including ACME) projecting the changes in gravity waves with continued warming:

Liu, H.-L., J. M. McInerney, S. Santos, P. H. Lauritzen, M. A. Taylor, and N. M. Pedatella (2014), "Gravity waves simulated by high-resolution Whole Atmosphere Community Climate Model", Geophys. Res. Lett., 41, 9106–9112, doi:10.1002/2014GL062468.

http://onlinelibrary.wiley.com/enhanced/doi/10.1002/2014GL062468/ (http://onlinelibrary.wiley.com/enhanced/doi/10.1002/2014GL062468/)

Abstract: "For the first time a mesoscale-resolving whole atmosphere general circulation model has been developed, using the National Center for Atmospheric Research Whole Atmosphere Community Climate Model with ∼0.25° horizontal resolution and 0.1 scale height vertical resolution above the middle stratosphere (higher resolution below). This is made possible by the high accuracy and high scalability of the spectral element dynamical core from the High-Order Method Modeling Environment. For the simulated January–February period, the latitude-height structure and the magnitudes of the temperature variance compare well with those deduced from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) observations. The simulation reveals the increasing dominance of gravity waves (GWs) at higher altitudes through both the height dependence of the kinetic energy spectra, which display a steeper slope (∼−3) in the stratosphere and an increasingly shallower slope above, and the increasing spatial extent of GWs (including a planetary-scale extent of a concentric GW excited by a tropical cyclone) at higher altitudes. GW impacts on the large-scale flow are evaluated in terms of zonal mean zonal wind and tides: with no GW drag parameterized in the simulations, forcing by resolved GWs does reverse the summer mesospheric wind, albeit at an altitude higher than climatology, and only slows down the winter mesospheric wind without closing it. The hemispheric structures and magnitudes of diurnal and semidiurnal migrating tides compare favorably with observations."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 10, 2015, 12:41:13 AM
The linked reference emphasizes the importance of using a high resolution wind model when trying to project the amount of oceanic heat advected to Antarctic ice shelves and subsequently the amount of associated ice mass loss.

Michael S. Dinniman, John M. Klinck, Le-Sheng Bai, David H. Bromwich, Keith M. Hines, and David M. Holland (2015), "The effect of atmospheric forcing resolution on delivery of ocean heat to the Antarctic floating ice shelves", Journal of Climate, doi: http://dx.doi.org/10.1175/JCLI-D-14-00374.1 (http://dx.doi.org/10.1175/JCLI-D-14-00374.1)


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00374.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00374.1)


Abstract: "Oceanic melting at the base of the floating Antarctic ice shelves is now thought to be a more significant cause of mass loss for the Antarctic ice sheet than iceberg calving. In this study, we use a 10 km horizontal resolution circum-Antarctic ocean/sea ice/ice shelf model (based on ROMS) to study the delivery of ocean heat to the base of the ice shelves. The atmospheric forcing comes from the ERA-Interim reanalysis (~80 km resolution) and from simulations using the Polar-optimized Weather Research and Forecasting model (30 km resolution) where the upper atmosphere was relaxed to the ERA-Interim reanalysis. The modeled total basal ice shelf melt is low compared to observational estimates, but increases by 14% with the higher resolution winds and just 3% with both the higher resolution winds and atmospheric surface temperatures. The higher resolution winds lead to more heat being delivered to the ice shelf cavities from the adjacent ocean and an increase in the efficiency of heat transfer between the water and the ice. The higher resolution winds also lead to changes in the heat delivered from the open ocean to the continental shelves as well as changes in the heat lost to the atmosphere over the shelves and the sign of these changes varies regionally. Addition of the higher resolution temperatures to the winds results in lowering, primarily during summer, the wind driven increase in heat advected into the ice shelf cavities due to colder summer air temperatures near the coast."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 15, 2015, 11:28:10 AM
As we are currently entering a period with a potentially strong El Nino event the following research can help us understand the associate changes in the currents around Antarctica (with implications for the potential acceleration of ice mass loss due to the accelerated advection of warm CDW to the grounding lines of key marine glaciers):

Clothilde E. Langlais, Stephen R. Rintoul, and Jan D. Zika, 2015: Sensitivity of Antarctic Circumpolar Current Transport and Eddy Activity to Wind Patterns in the Southern Ocean. J. Phys. Oceanogr., 45, 1051–1067; doi: http://dx.doi.org/10.1175/JPO-D-14-0053.1 (http://dx.doi.org/10.1175/JPO-D-14-0053.1)


http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-14-0053.1 (http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-14-0053.1)


Abstract: "The Southern Hemisphere westerly winds have intensified in recent decades associated with a positive trend in the southern annular mode (SAM). However, the response of the Antarctic Circumpolar Current (ACC) transport and eddy field to wind forcing remains a topic of debate. This study uses global eddy-permitting ocean circulation models driven with both idealized and realistic wind forcing to explore the response to interannual wind strengthening. The response of the barotropic and baroclinic transports and eddy field of the ACC is found to depend on the spatial pattern of the changes in wind forcing. In isolation, an enhancement of the westerlies over the ACC belt leads to an increase of both barotropic and baroclinic transport within the ACC envelope, with lagged enhancement of the eddy kinetic energy (EKE). In contrast, an increase in wind forcing near Antarctica drives a largely barotropic change in transport along closed f/H contours (“free mode”), with little change in eddy activity. Under realistic forcing, the interplay of the SAM and the El Niño–Southern Oscillation (ENSO) influences the spatial distribution of the wind anomalies, in particular the partition between changes in the wind stress over the ACC and along f/H contours. This study finds that the occurrence of a negative or positive ENSO during a positive SAM can cancel or double the wind anomalies near Antarctica, altering the response of the ACC and its eddy field. While a negative ENSO and positive SAM favors an increase in EKE, a positive ENSO and positive SAM lead to barotropic transport changes and no eddy response."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 16, 2015, 12:57:02 AM
The two attached images show some of the results of the Los Alamos National Laboratory's (LANL's) contributions to the ACME program.  The first image shows ocean currents & eddies in the Southern Ocean; while the second image shows an example of LANL's efforts to model the degradation of the permafrost with continued warming.

http://www.lanl.gov/newsroom/picture-of-the-week/pic-week-9.php (http://www.lanl.gov/newsroom/picture-of-the-week/pic-week-9.php)

Caption for first Image: "The oceans play an important role in the earth's climate; they transport heat from equator to pole, provide moisture for rain, and absorb carbon dioxide from the atmosphere. Ocean models, such as this one from Los Alamos National Laboratory, help explain interactions between individual eddies that may be altered in a changing climate. This visualization, courtesy of the Lab's MPAS-Ocean Model, shows ocean currents and eddies in a high-resolution global ocean simulation with the Antarctic in the center. Colors show speed, where white is fast and blue is slow."

http://www.lanl.gov/newsroom/picture-of-the-week/pic-week-8.php (http://www.lanl.gov/newsroom/picture-of-the-week/pic-week-8.php)

Caption for second Image: "Arctic soils currently store nearly 20 years worth of human emissions of carbon in frozen permafrost, but the Arctic is warming faster than most of the rest of the Earth, meaning that this carbon may soon thaw and be released as greenhouse gases. Los Alamos National Laboratory scientists work to understand the fate of this carbon using computer simulations such as this model of snowmelt draining from polygonal ground near Barrow, Alaska."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 06, 2015, 01:21:04 AM
The linked reference provides new insight on modeling the ACC and the Southern Ocean MOC:

Farneti, R., S.M. Downes, S.M. Griffies, S.J. Marsland, E. Behrens, M. Bentsen, D. Bi, A. Biastoch, C. Böning, A. Bozec, V.M. Canuto, E. Chassignet, G. Danabasoglu, S. Danilov, N. Diansky, H. Drange, P.G. Fogli, A. Gusev, R.W. Hallberg, A. Howard, M. Ilicak, T. Jung, M. Kelley, W.G. Large, A. Leboissetier, M. Long, J. Lu, S. Masina, A. Mishra, A. Navarra, A.J. George Nurser, L. Patara, B.L. Samuels, D. Sidorenko, H. Tsujino, P. Uotila, Q. Wang, and S.G. Yeager (2015), "An assessment of Antarctic Circumpolar Current and Southern Ocean Meridional Overturning Circulation during 1958-2007 in a suite of interannual CORE-II simulations", Ocean Model., doi:10.1016/j.ocemod.2015.07.009.

http://www.sciencedirect.com/science/article/pii/S1463500315001183 (http://www.sciencedirect.com/science/article/pii/S1463500315001183)

Abstract: "In the framework of the second phase of the Coordinated Ocean-ice Reference Experiments (CORE-II), we present an analysis of the representation of the Antarctic Circumpolar Current (ACC) and Southern Ocean Meridional Overturning Circulation (MOC) in a suite of seventeen global ocean-sea ice models. We focus on the mean, variability and trends of both the ACC and MOC over the 1958-2007 period, and discuss their relationship with the surface forcing. We aim to quantify the degree of eddy saturation and eddy compensation in the models participating in CORE-II, and compare our results with available observations, previous fine-resolution numerical studies and theoretical constraints. Most models show weak ACC transport sensitivity to changes in forcing during the past five decades, and they can be considered to be in an eddy saturated regime. Larger contrasts arise when considering MOC trends, with a majority of models exhibiting significant strengthening of the MOC during the late 20th and early 21st century. Only a few models show a relatively small sensitivity to forcing changes, responding with an intensified eddy-induced circulation that provides some degree of eddy compensation, while still showing considerable decadal trends. Both ACC and MOC interannual variability are largely controlled by the Southern Annular Mode (SAM). Based on these results, models are clustered into two groups. Models with constant or two-dimensional (horizontal) specification of the eddy-induced advection coefficient κ show larger ocean interior decadal trends, larger ACC transport decadal trends and no eddy compensation in the MOC. Eddy-permitting models or models with a three-dimensional time varying κ show smaller changes in isopycnal slopes and associated ACC trends, and partial eddy compensation. As previously argued, a constant in time or space κ is responsible for a poor representation of mesoscale eddy effects and cannot properly simulate the sensitivity of the ACC and MOC to changing surface forcing. Evidence is given for a larger sensitivity of the MOC as compared to the ACC transport, even when approaching eddy saturation. Future process studies designed for disentangling the role of momentum and buoyancy forcing in driving the ACC and MOC are proposed.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 11, 2015, 12:59:13 AM
The linked reference indicates that model results show that the Southern Hemisphere Hadley cell is expanding due to GHG forcing:

H. Nguyen, C. Lucas, A. Evans, B. Timbal, and L. Hanson (2015), "Expansion of the Southern Hemisphere Hadley Cell in response to greenhouse gas forcing", Journal of Climate, doi: http://dx.doi.org/10.1175/JCLI-D-15-0139.1 (http://dx.doi.org/10.1175/JCLI-D-15-0139.1)


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0139.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0139.1)


Abstract: "Changes of the southern hemisphere Hadley cell over the twentieth Century are investigated using the twentieth Century Reanalysis (20CR) and coupled model simulations from the Coupled Model Intercomparison Project phase 5 (CMIP5). Trends computed on a 30-year sliding window on the 20CR dataset reveal a statistically significant expansion of the Hadley cell from 1968 forced by an increasing surface global warming. This expansion is strongly associated with the intensification and poleward shift of the subtropical dry zone, which potentially explain the increasing trends of droughts in the subtropical regions such as Southern Australia, South America and Africa. Coupled models from the CMIP5 do not adequately simulate the observed amount of the Hadley expansion, only showing an average of one fourth of the expansion as determined from the 20CR and only when simulations include greenhouse gas forcing as opposed to simulations including natural forcing only."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 27, 2015, 12:12:28 AM
The linked reference provides new insight on the roles of the different tropical ocean basins on telecommunication of energy to the West Antarctic Ice Sheet.  However, while the reference correctly models many responses they acknowledge that still better understanding needs to be gain about the associate jet stream structure that are influence by a large number of phenomena including the: ENSO, IPO, PDO, AMO, SAM, the ozone hole, global warming, ocean currents, cyclonic activity etc. etc.; all of which could influence ice mass loss rates from the WAIS in the future.

Xichen Li, David M. Holland, Edwin P. Gerber and Changhyun Yoo (2015), "Rossby waves mediate impacts of tropical oceans on West Antarctic atmospheric circulation in austral winter", Journal of Climate; doi: http://dx.doi.org/10.1175/JCLI-D-15-0113.1 (http://dx.doi.org/10.1175/JCLI-D-15-0113.1)



http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0113.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0113.1)


Abstract: "Recent studies link climate change around Antarctica to the sea surface temperature of tropical oceans, with teleconnections from the Pacific, Atlantic, and Indian Oceans making different contributions to Antarctic climate. In this study, we identify the impacts of each ocean basin on the wintertime Southern Hemisphere circulation, by comparing simulation results using a comprehensive atmospheric model, an idealized dynamical core model, and a theoretical Rossby-wave model. Our results show that Tropical Atlantic Ocean warming, Indian Ocean warming, and Eastern Pacific cooling are all able to deepen the Amundsen Sea Low located adjacent to West Antarctica, while Western Pacific warming increases the pressure to the west of the international date line, encompassing the Ross Sea and regions south of the Tasman Sea. In austral winter, these tropical ocean basins work together linearly to modulate the atmospheric circulation around Western Antarctica. Further analyses indicate that these teleconnections critically depend on stationary Rossby-wave dynamics, and are thus sensitive to the background flow, in particular, the sub-tropical/mid-latitude jet. Near these jets, wind shear is amplified, which strengthens the generation of Rossby waves. On the other hand, near the edges of the jets, the meridional gradient of the absolute vorticity is also enhanced. As a consequence of the Rossby-wave dispersion relationship, the jet edge may reflect stationary Rossby-wave trains, serving as a wave-guide. Our simulation results not only identify the relative roles of each of the tropical ocean basins in the tropical – Antarctica teleconnection, but also suggest that a deeper understanding of teleconnections requires a better estimation of the atmospheric jet structures."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on September 14, 2015, 08:07:39 PM
The linked reference finds that considering only hosing from the PIG collapse is sufficient to alter climate model projections for such matters as: CDW temperatures, surface water temperatures, Southern Ocean sea ice extent, and AMOC activity.  This work clearly substantiates the Hansen et al. 2015 findings, and also indicates how sensitive climate response is to different input combinations:

J.A.M. Green and A. Schmittner (2015), "Climatic consequences of a Pine Island Glacier collapse", Journal of Climate; doi: http://dx.doi.org/10.1175/JCLI-D-15-0110.1 (http://dx.doi.org/10.1175/JCLI-D-15-0110.1)


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0110.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0110.1)


Abstract: "An intermediate complexity climate model is used to simulate the impact of an accelerated Pine Island Glacier mass loss on the large-scale ocean circulation and climate. Simulations are performed for pre-industrial conditions using hosing levels consistent with present day observation of 3,000 m3 s-1, at an accelerated rate of 6,000 m3 s-1, and at a total collapse rate of 100,000 m3 s-1, and in all experiments the hosing lasted 100 years. It is shown that even a modest input of meltwater from the glacier can introduce an initial cooling over the upper part of the Southern Ocean due to increased stratification and ice cover leading to a reduced upward heat flux from Circumpolar Deep Water. This causes global ocean heat content to increase and global surface air temperatures to decrease. The Atlantic Meridional Overturning Circulation (AMOC) increases, presumably due to changes in the density difference between Antarctic Intermediate Water and North Atlantic Deep Water. Simulations with a simultaneous hosing and increases of atmospheric CO2 concentrations show smaller effects of the hosing on global surface air temperature and ocean heat content, which we attribute to the melting of Southern Ocean sea ice. The sensitivity of the AMOC to the hosing is also reduced as the warming by the atmosphere completely dominates the perturbations."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on November 27, 2015, 05:32:37 PM
With a hat-tip to Laurent, I re-post the following from the "What's new in Antarctica?" thread:

Big data reveals glorious animation of Antarctic bottom water
http://nci.org.au/2015/11/24/big-data-reveals-glorious-animation-of-antarctic-bottom-water/ (http://nci.org.au/2015/11/24/big-data-reveals-glorious-animation-of-antarctic-bottom-water/)

https://www.youtube.com/watch?feature=player_embedded&v=8VMSF28J9H4 (https://www.youtube.com/watch?feature=player_embedded&v=8VMSF28J9H4)
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on January 05, 2016, 08:17:38 PM
The linked article discusses a ground based initiative to gather high-quality data about Antarctic clouds; which are critical for the accurate calibration of regional models:

Alexandra Witze  (07 January 2016), "Antarctic clouds studied for first time in five decades
AWARE project will help unravel effects of global warming", Nature, Volume: 529, Pages: 12, doi:10.1038/529012a


http://www.nature.com/news/antarctic-clouds-studied-for-first-time-in-five-decades-1.19110 (http://www.nature.com/news/antarctic-clouds-studied-for-first-time-in-five-decades-1.19110)

Extract: "On Antarctica’s Ross Island, a short drive from the US McMurdo research station, high-tech radar antennas and other atmospheric instruments gaze skyward, gathering detailed measurements of West Antarctic clouds. Remarkably, these are the first such data to be gathered in five decades — even though weather patterns in the region can influence those half a world away.
The US$5-million project, known as the Atmospheric Radiation Measurement West Antarctic Radiation Experiment (AWARE), began to observe the skies near McMurdo in November and will run until early 2017. A second measurement station, 1,600 kilometres away in the ice sheet’s interior, will operate until the end of this month. (The site is so remote that it can be used only during the Antarctic summer.)
A similar experiment in the Arctic in 1997–98 relied on an instrument-laden ship that was deliberately frozen into sea ice. It yielded fundamental insights into the physics of northern polar clouds, and AWARE scientists hope that their project will do the same for the south. “This is going to be a sea change in our understanding,” says Lynn Russell, an atmospheric scientist at the Scripps Institution of Oceanography in La Jolla, California, and a co-principal investigator on AWARE.
Antarctica’s massive ice sheet acts as a global heat sink. As a result, changes in Antarctic clouds, such as the amount of ground they cover or how much radiation they absorb, can have ripple effects as far away as the tropics. Climate modellers need to understand the physics of these clouds if they are to correctly work out how weather around the globe will change as the polar regions warm.

AWARE, which is led by Scripps atmospheric scientist Dan Lubin, aims to get the best data yet on clouds and aerosol particles above West Antarctica. That includes mixed phase clouds, which occur in polar regions and combine supercooled water with ice. Studies have shown that clouds moving across Antarctica’s interior are mostly ice, whereas those moving onshore from the coast contain more liquid water. The composition of these clouds plays a major part in determining how much sunlight they reflect into space — which helps to shape atmospheric circulation and weather patterns below."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on January 24, 2016, 03:52:02 AM
The linked reference discusses new model results about Mechanisms of Southern Ocean heat uptake and transport; which indicate to me that heat sequestered in the deep ocean in Antarctica does not stay sequestered as long as previously thought due to global eddying that results in mixing:


Adele K. Morrison, Stephen M. Griffies, Michael Winton, and Whit G. Anderson & Jorge L. Sarmiento (2016 ), "Mechanisms of Southern Ocean heat uptake and transport in a global eddying climate model", Journal of Climate, doi: http://dx.doi.org/10.1175/JCLI-D-15-0579.1 (http://dx.doi.org/10.1175/JCLI-D-15-0579.1)


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0579.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0579.1)

Abstract: "The Southern Ocean plays a dominant role in anthropogenic oceanic heat uptake. Strong northward transport of the heat content anomaly limits warming of the sea surface temperature in the uptake region and allows the heat uptake to be sustained. Using an eddy-rich global climate model, the processes controlling the northward transport and convergence of the heat anomaly in the mid-latitude Southern Ocean are investigated in an idealized 1% yr−1 increasing CO2 simulation. Heat budget analyses reveal that different processes dominate to the north and south of the main convergence region. The heat transport northward from the uptake region in the south is driven primarily by passive advection of the heat content anomaly by the existing time mean circulation, with a smaller 20% contribution from enhanced upwelling. The heat anomaly converges in the mid-latitude deep mixed layers, because there is not a corresponding increase in the mean heat transport out of the deep mixed layers northward into the mode waters. To the north of the deep mixed layers, eddy processes drive the warming and account for nearly 80% of the northward heat transport anomaly. The eddy transport mechanism results from a reduction in both the diffusive and advective southward eddy heat transports, driven by decreasing isopycnal slopes and decreasing along-isopycnal temperature gradients on the northern edge of the peak warming."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on January 29, 2016, 02:41:33 PM
The linked reference introduces freshwater flux into a CESM1-CAM5 model (i.e. hosing, which was not included in the CMIP5 projections) to produce updated projections indicating that currently the relatively small amounts of freshwater introduced to the Southern Ocean by Antarctic Ice Sheet mass loss is contributing to sea ice extent expansion; but that this trend will reverse itself over a period of 20-years (or longer) due to global warming (even if the freshwater flux/hosing increases several times and/or at different water depths).  This finding could represent a worse-case scenario for abrupt sea level contribution from the WAIS, as it promotes the accumulation of warm CDW in the Southern Ocean for the time being (which facilitates grounding line retreat for heat marine glacier) followed by subsequent sea ice reductions that will both:
(a) Promote austral summer surface ice melting (due to reduced summertime albedo) and associated hydrofracturing, and
(b) Reduce the amount of land fast sea ice that can pin icebergs in place.  This would result in the loss of buttressing action from the associated ice mélange.

Andrew G. Pauling, Cecilia M. Bitz, Inga J. Smith and Patricia J. Langhorne (2016), "The Response of the Southern Ocean and Antarctic Sea Ice to Fresh Water from Ice Shelves in an Earth System Model", Journal of Climate, doi: http://dx.doi.org/10.1175/JCLI-D-15-0501.1 (http://dx.doi.org/10.1175/JCLI-D-15-0501.1)


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0501.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0501.1)


Abstract: "The possibility that recent Antarctic sea ice expansion resulted from an increase in fresh water reaching the Southern Ocean is investigated here. The freshwater flux from ice sheet and ice shelf mass imbalance is largely missing in models that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5). However, on average P-E reaching the Southern Ocean has increased in CMIP5 models to a present value that is about 2600 Gt yr−1 greater than pre-industrial times and 5-22 times larger than estimates of the mass imbalance of Antarctic ice sheets and shelves (119 to 544 Gt yr−1). Two sets of experiments were conducted from 1980-2013 in CESM1-CAM5, one of the CMIP5 models, artificially distributing fresh water either at the ocean surface to mimic iceberg melt, or at the ice shelf fronts at depth. An anomalous reduction in vertical advection of heat into the surface mixed layer resulted in sea surface cooling at high southern latitudes, and an associated increase in sea ice area. Enhancing the freshwater input by an amount within the range of estimates of the Antarctic mass imbalance did not have any significant effect on either sea ice area magnitude or trend. Freshwater enhancement of 2000 Gt yr−1 raised the total sea ice area by 1×106 km2, yet this and even an enhancement of 3000 Gt yr−1 was insufficient to offset the sea ice decline due to anthropogenic forcing for any period of 20 years or longer. Further, the sea ice response was found to be insensitive to the depth of fresh water injection."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on April 08, 2016, 05:03:44 PM
The linked reference corrects a long know bias in the CESM regarding ASR for the Southern Ocean.  This correction resulted in a pre-industrial era increase in tropical temperatures and a decrease in Southern Ocean temperatures:

Jennifer E. Kay, Casey Wall, Vineel Yettella, Brian Medeiros, Cecile Hannay, Peter Caldwell and Cecilia Bitz (2016), "Global climate impacts of fixing the Southern Ocean shortwave radiation bias in the Community Earth System Model (CESM)",  Journal of Climate, doi: 10.1175/JCLI-D-15-0358.1.

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0358.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0358.1)

Abstract: "A large, long-standing, and pervasive climate model bias is excessive absorbed shortwave radiation (ASR) over the mid-latitude oceans, especially the Southern Ocean. This study investigates both the underlying mechanisms for and climate impacts of this bias within the Community Earth System Model with the Community Atmosphere Model version 5 (CESM-CAM5). Excessive Southern Ocean ASR in CESM-CAM5 results in part because low-level clouds contain insufficient amounts of supercooled liquid. In a present-day atmosphere-only run, an observationally motivated modification to the shallow convection detrainment increases supercooled cloud liquid, brightens low-level clouds, and substantially reduces the Southern Ocean ASR bias. Tuning to maintain global energy balance enables reduction of a compensating tropical ASR bias. In the resulting pre-industrial fully coupled run with a brighter Southern Ocean and dimmer Tropics, the Southern Ocean cools and the Tropics warm. As a result of the enhanced meridional temperature gradient, poleward heat transport increases in both hemispheres (especially the Southern Hemisphere) and the Southern Hemisphere atmospheric jet strengthens. Because Northward cross-equatorial heat transport reductions occur primarily in the ocean (80%) not the atmosphere (20%), a proposed atmospheric teleconnection linking Southern Ocean ASR bias reduction and cooling with northward shifts in tropical precipitation has little impact. In summary, observationally motivated supercooled liquid water increases in shallow convective clouds enable large reductions in long-standing climate model shortwave radiation biases. Of relevance to both model bias reduction and climate dynamics, quantifying the influence of Southern Ocean cooling on tropical precipitation requires a model with dynamic ocean heat transport."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on April 23, 2016, 07:06:06 PM
As both of the linked references are on the technical side I am posting them in this thread; however, they both could be seen as support Hansen et al (2016)'s ice-climate feedback mechanism if their findings were to be incorporated within a suitable climate model:

K. Hutchinson, S. Swart, A. Meijers, I. Ansorge & S. Speich (19 April 2016), "Decadal-scale thermohaline variability in the Atlantic sector of the Southern Ocean", Journal of Geophysical Research Oceans, DOI: 10.1002/2015JC011491


http://onlinelibrary.wiley.com/doi/10.1002/2015JC011491/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2015JC011491/abstract)

Abstract: "An enhanced Altimetry Gravest Empirical Mode (AGEM), including both adiabatic and diabatic trends, is developed for the Antarctic Circumpolar Current (ACC) south of Africa using updated hydrographic CTD sections, Argo data, and satellite altimetry. This AGEM has improved accuracy compared to traditional climatologies and other proxy methods. The AGEM for the Atlantic Southern Ocean offers an ideal technique to investigate the thermohaline variability over the past two decades in a key region for water mass exchanges and transformation. In order to assess and attribute changes in the hydrography of the region, we separate the changes into adiabatic and diabatic components. Integrated over the upper 2000 dbar of the ACC south of Africa, results show mean adiabatic changes of 0.16 ± 0.11°C.decade−1 and 0.006 ± 0.014 decade−1, and diabatic differences of -0.044 ± 0.13°C.decade−1 and -0.01 ± 0.017 .decade−1 for temperature and salinity, respectively. The trends of the resultant AGEM, that include both adiabatic and diabatic variability (termed AD-AGEM), show a significant increase in the heat content of the upper 2000dbar of the ACC with a mean warming of 0.12 ± 0.087°C.decade−1. This study focuses on the Antarctic Intermediate Water (AAIW) mass where negative diabatic trends dominate positive adiabatic differences in the Subantarctic Zone (SAZ), with results indicating a cooling (-0.17°C.decade−1) and freshening (-0.032 decade−1) of AAIW in this area, whereas south of the SAZ positive adiabatic and diabatic trends together create a cumulative warming (0.31°C.decade−1) and salinification (0.014 decade−1) of AAIW."

Patrick F. Cummins, Diane Masson & Oleg A. Saenko (21 April 2016), "Vertical heat flux in the ocean: Estimates from observations and from a coupled general circulation model", Journal of Geophysical Research Oceans, DOI: 10.1002/2016JC011647

http://onlinelibrary.wiley.com/doi/10.1002/2016JC011647/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2016JC011647/abstract)

Abstract: ”The net heat uptake by the ocean in a changing climate involves small imbalances between the advective and diffusive processes that transport heat vertically. Generally, it is necessary to rely on global climate models to study these processes in detail. In the present study, it is shown that a key component of the vertical heat flux, namely that associated with the large-scale mean vertical circulation, can be diagnosed over extra-tropical regions from global observational data sets. This component is estimated based on the vertical velocity obtained from the geostrophic vorticity balance, combined with estimates of absolute geostrophic flow. Results are compared with the output of a non-eddy resolving, coupled atmosphere-ocean general circulation model. Reasonable agreement is found in the latitudinal distribution of the vertical heat flux, as well as in the area-integrated flux below about 250 meters depth. The correspondence with the coupled model deteriorates sharply at depths shallower than 250 m due to the omission of equatorial regions from the calculation. The vertical heat flux due to the mean circulation is found to be dominated globally by the downward contribution from the Southern Hemisphere, in particular the Southern Ocean. This is driven by the Ekman vertical velocity which induces an upward transport of seawater that is cold relative to the horizontal average at a given depth. The results indicate that the dominant characteristics of the vertical transport of heat due to the mean circulation can be inferred from simple linear vorticity dynamics over much of the ocean."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on May 27, 2016, 10:50:07 PM
The linked (open access) reference focuses on the impacts of marine instability primarily of the Wilkes Basin (but also other basins as indicated by the attached images showing impacts on AABW formation due to different assumed marine glacier instability scenarios in different basins) on Southern Ocean dynamics.  This research supports the Hansen et al (2016) findings:

Phipps, S. J., Fogwill, C. J., and Turney, C. S. M.: Impacts of marine instability across the East Antarctic Ice Sheet on Southern Ocean dynamics, The Cryosphere Discuss., doi:10.5194/tc-2016-111, in review, 2016.

http://www.the-cryosphere-discuss.net/tc-2016-111/ (http://www.the-cryosphere-discuss.net/tc-2016-111/)

Abstract. Recent observations and modelling studies have demonstrated the potential for rapid and substantial retreat of large sectors of the East Antarctic Ice Sheet (EAIS). This has major implications for ocean circulation and global sea level. Here we examine the effects of increasing meltwater from the Wilkes Basin, one of the major marine-based sectors of the EAIS, on Southern Ocean dynamics. Climate model simulations reveal that the meltwater flux rapidly stratifies surface waters, leading to a dramatic decrease in the rate of Antarctic Bottom Water formation. The surface ocean cools but, critically, the Southern Ocean warms by more than 1 ºC at depth. This warming is accompanied by a Southern Ocean-wide "domino effect", whereby the warming signal propagates westward with depth. Our results suggest that melting of one sector of the EAIS could result in accelerated warming across other sectors, including the Weddell Sea sector of the West Antarctic Ice Sheet. Thus localised melting of the EAIS could potentially destabilise the wider Antarctic Ice Sheet.


Caption for attached image: "Figure 3. Rate of AABW formation (Sv) in the control simulation (black), and in experiments WILKES (red), WEST (green) and EAST (blue). Thin lines indicate individual ensemble members; thick lines indicate the ensemble means. The values shown are 100-year running means. Vertical dashed lines indicate the years in which the freshwater hosing begins and ends."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on June 02, 2016, 04:55:51 AM
Calibrating ESMs (like ACME) to match the rather abrupt change in ocean circulation patterns observed for the PETM, may contribute to our confidence that such models can accurately project where we are headed in the coming decades:

Abbott, A. N., Haley, B. A., Tripati, A. K., and Frank, M.: Constraints on ocean circulation at the Paleocene–Eocene Thermal Maximum from neodymium isotopes, Clim. Past, 12, 837-847, doi:10.5194/cp-12-837-2016, 2016.


http://www.clim-past.net/12/837/2016/cp-12-837-2016.pdf (http://www.clim-past.net/12/837/2016/cp-12-837-2016.pdf)

Abstract. Global warming during the Paleocene–Eocene Thermal Maximum (PETM)  ∼  55 million years ago (Ma) coincided with a massive release of carbon to the ocean–atmosphere system, as indicated by carbon isotopic data. Previous studies have argued for a role of changing ocean circulation, possibly as a trigger or response to climatic changes. We use neodymium (Nd) isotopic data to reconstruct short high-resolution records of deep-water circulation across the PETM. These records are derived by reductively leaching sediments from seven globally distributed sites to reconstruct past deep-ocean circulation across the PETM. The Nd data for the leachates are interpreted to be consistent with previous studies that have used fish teeth Nd isotopes and benthic foraminiferal δ13C to constrain regions of convection. There is some evidence from combining Nd isotope and δ13C records that the three major ocean basins may not have had substantial exchanges of deep waters. If the isotopic data are interpreted within this framework, then the observed pattern may be explained if the strength of overturning in each basin varied distinctly over the PETM, resulting in differences in deep-water aging gradients between basins. Results are consistent with published interpretations from proxy data and model simulations that suggest modulation of overturning circulation had an important role for initiation and recovery of the ocean–atmosphere system associated with the PETM.

Edit: For those who do not like to click on open access references, I provide both the first associated image of Fig 1 with the following caption: "Figure 1. Nd and C isotope data ("Nd and _13C) across the PETM from the Southern Ocean (a), Pacific Ocean (b), and Atlantic Ocean (c).  The sediment leach "Nd are shown with circles and solid lines; the fish teeth/debris "Nd from Thomas et al. (2003) are shown as dots. All data are presented on directly comparable scales for both "Nd and _13C. The sample ages are based on the _13C age models. In (b) the age model of Site 1209B has been slightly adjusted (second x axis) such that the _13C excursion coincides with the age of the PETM in the other cores. The shaded vertical bar indicates the timing of the PETM as defined by the CIE in the cores."  Also, I provide the second attached image of Fig 3.  Both of these images show the relatively high sensitivity of ocean currents following the PETM triggering event, particularly with regards to upwelling in the Southern Ocean and along the west coast of South America. 
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on June 09, 2016, 05:29:03 PM
The linked reference provides field data from deep diving elephant seals to better characterize the nature and movements of the modified CDW that is crossing the continental shelves in West Antarctica to cause basal ice melting for associated ice shelves and grounding line retreat for key marine glaciers:

Xiyue Zhang, Andrew F. Thompson, Mar M. Flexas, Fabien Roquet & Horst Bornemann (1 June 2016), "Circulation and meltwater distribution in the Bellingshausen Sea: from shelf break to coast", Geophysical Research Letters, DOI: 10.1002/2016GL068998

http://onlinelibrary.wiley.com/doi/10.1002/2016GL068998/full (http://onlinelibrary.wiley.com/doi/10.1002/2016GL068998/full)

Abstract: "West Antarctic ice shelves have thinned dramatically over recent decades. Oceanographic measurements that explore connections between offshore warming and transport across a continental shelf with variable bathymetry towards ice shelves are needed to constrain future changes in melt rates. Six years of seal-acquired observations provide extensive hydrographic coverage in the Bellingshausen Sea, where ship-based measurements are scarce. Warm but modified Circumpolar Deep Water floods the shelf and establishes a cyclonic circulation within the Belgica Trough with flow extending towards the coast along the eastern boundaries and returning to the shelf break along western boundaries. These boundary currents are the primary water mass pathways that carry heat towards the coast and advect ice shelf meltwater offshore. The modified Circumpolar Deep Water and meltwater mixtures shoal and thin as they approach the continental slope before flowing westward at the shelf break, suggesting the presence of the Antarctic Slope Current. Constraining meltwater pathways is a key step in monitoring the stability of the West Antarctic Ice Sheet."


See also:
https://www.washingtonpost.com/news/energy-environment/wp/2016/06/08/seals-wearing-little-sensors-are-showing-scientists-why-antarctica-is-melting/ (https://www.washingtonpost.com/news/energy-environment/wp/2016/06/08/seals-wearing-little-sensors-are-showing-scientists-why-antarctica-is-melting/)
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on June 29, 2016, 09:01:22 PM

The linked PowerPoint presentation discusses the atmospheric response to the Weddell Polynya (the attached image shows this polynya in the 1970's):

 Weijer, Veneziani, Hecht, Jeffery, Jonko, Stössel & Hodos (2016) "Atmospheric Response to the Weddell Polynya"

http://climatemodeling.science.energy.gov/sites/default/files/presentations/Wilbert_Polynyas.pdf (http://climatemodeling.science.energy.gov/sites/default/files/presentations/Wilbert_Polynyas.pdf)

Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on July 01, 2016, 11:09:57 PM
As a follow-on to my Reply #100, the linked open access pdf describes a recently initiated field campaign to gather direct atmospheric data (generally related to cloud cover & radivative forcing) between the WAIS Divide & McMurdo Station.  The document is entitled: "ARM West Antarctic Radiation Experiment (AWARE) Science Plan", and hopefully finding from this effort will improve regional modeling of cloud cover in West Antarctica (as most current climate models exhibit low skill levels in this area):

https://www.arm.gov/publications/programdocs/doe-sc-arm-15-040.pdf (https://www.arm.gov/publications/programdocs/doe-sc-arm-15-040.pdf)

Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: sidd on October 19, 2016, 01:09:54 AM
http://www.ocean-sci-discuss.net/os-2016-54/ (http://www.ocean-sci-discuss.net/os-2016-54/)

discusses AAIW freshening, decreasing Agulhas leakage and more. paper is open access, in review stage.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on December 12, 2016, 06:43:47 PM
The linked reference provides field evidence supporting Hansen's ice-climate interaction mechanism.

Pepijn Bakker et al, Centennial-scale Holocene climate variations amplified by Antarctic Ice Sheet discharge, Nature (2016). DOI: 10.1038/nature20582

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature20582.html (http://www.nature.com/nature/journal/vaop/ncurrent/full/nature20582.html)

Abstract: "Proxy-based indicators of past climate change show that current global climate models systematically underestimate Holocene-epoch climate variability on centennial to multi-millennial timescales, with the mismatch increasing for longer periods. Proposed explanations for the discrepancy include ocean–atmosphere coupling that is too weak in models, insufficient energy cascades from smaller to larger spatial and temporal scales, or that global climate models do not consider slow climate feedbacks related to the carbon cycle or interactions between ice sheets and climate. Such interactions, however, are known to have strongly affected centennial- to orbital-scale climate variability during past glaciations, and are likely to be important in future climate change. Here we show that fluctuations in Antarctic Ice Sheet discharge caused by relatively small changes in subsurface ocean temperature can amplify multi-centennial climate variability regionally and globally, suggesting that a dynamic Antarctic Ice Sheet may have driven climate fluctuations during the Holocene. We analysed high-temporal-resolution records of iceberg-rafted debris derived from the Antarctic Ice Sheet, and performed both high-spatial-resolution ice-sheet modelling of the Antarctic Ice Sheet and multi-millennial global climate model simulations. Ice-sheet responses to decadal-scale ocean forcing appear to be less important, possibly indicating that the future response of the Antarctic Ice Sheet will be governed more by long-term anthropogenic warming combined with multi-centennial natural variability than by annual or decadal climate oscillations."


See also the linked article entitled: "Antarctic Ice Sheet study reveals 8,000-year record of climate change".

http://phys.org/news/2016-12-antarctic-ice-sheet-reveals-year.html (http://phys.org/news/2016-12-antarctic-ice-sheet-reveals-year.html)

Extract: "An international team of researchers has found that the Antarctic Ice Sheet plays a major role in regional and global climate variability - a discovery that may also help explain why sea ice in the Southern Hemisphere has been increasing despite the warming of the rest of the Earth.


Global climate models that look at the last several thousand years have failed to account for the amount of climate variability captured in the paleoclimate record, according to lead author Pepijn Bakker, a climate modeller from the MARUM Center for Marine Environmental Studies at the University of Bremen in Germany.

The researchers first turned their attention to the Scotia Sea. "Most icebergs calving off the Antarctic Ice Sheet travel through this region because of the atmospheric and oceanic circulation," explained Weber. "The icebergs contain gravel that drop into the sediment on the ocean floor - and analysis and dating of such deposits shows that for the last 8,000 years, there were centuries with more gravel and those with less."

The research team's hypothesis is that climate modellers have historically overlooked one crucial element in the overall climate system. They discovered that the centuries-long phases of enhanced and reduced Antarctic ice mass loss documented over the past 8,000 years have had a cascading effect on the entire climate system.

Using sophisticated computer modelling, the researchers traced the variability in iceberg calving (ice that breaks away from glaciers) to small changes in ocean temperatures."


See also the following linked article entitled: "New study shows impact of Antarctic Ice Sheet on climate change"

https://www.eurekalert.org/pub_releases/2016-12/osu-nss120816.php (https://www.eurekalert.org/pub_releases/2016-12/osu-nss120816.php)
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on February 17, 2017, 03:40:12 PM
The linked open access reference uses a model to likely associate eddies in the Southern Ocean to atmospheric CO₂ content.

David P. Marshall, Maarten H. P. Ambaum, James R. Maddison, David R. Munday & Lenka Novak (9 January 2017), "Eddy saturation and frictional control of the Antarctic Circumpolar Current", Geophysical Research Letters, DOI: 10.1002/2016GL071702

http://onlinelibrary.wiley.com/doi/10.1002/2016GL071702/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2016GL071702/abstract)

Abstract: "The Antarctic Circumpolar Current is the strongest current in the ocean and has a pivotal impact on ocean stratification, heat content, and carbon content. The circumpolar volume transport is relatively insensitive to surface wind forcing in models that resolve turbulent ocean eddies, a process termed “eddy saturation.” Here a simple model is presented that explains the physics of eddy saturation with three ingredients: a momentum budget, a relation between the eddy form stress and eddy energy, and an eddy energy budget. The model explains both the insensitivity of circumpolar volume transport to surface wind stress and the increase of eddy energy with wind stress. The model further predicts that circumpolar transport increases with increased bottom friction, a counterintuitive result that is confirmed in eddy-permitting calculations. These results suggest an unexpected and important impact of eddy energy dissipation, through bottom drag or lee wave generation, on ocean stratification, ocean heat content, and potentially atmospheric CO2."

See also the associated EOS article entitled: "Swirling Eddies in the Antarctic May Have Global Impacts"

https://eos.org/research-spotlights/swirling-eddies-in-the-antarctic-may-have-global-impacts?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz021717 (https://eos.org/research-spotlights/swirling-eddies-in-the-antarctic-may-have-global-impacts?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz021717)

Extract: "A new model examines how eddies in the Antarctic Circumpolar Current affect volume transport of the world's strongest current.

According to the authors, because of the ACC’s high-volume transport, this eddy energy dissipation in the Southern Ocean may have an outsized impact on global oceanic stratification and heat content. Because ocean stratification in turn impacts the ocean carbon cycle, the authors emphasize the potential role of these eddies in influencing atmospheric CO2. Further research into the mechanisms behind the current’s movement will help scientists to more fully understand the complex interactions between Earth’s oceans and atmosphere."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on July 15, 2017, 04:19:34 PM
I do not find it reassuring that the behavior of the Southern Ocean plays large roles in both Frey & Kay (2017)'s estimate of an ECS of 5.6C and in Hansen et al (2016)'s ice-climate feedback mechanism, and yet scientists do not adequately understand the decadal variability of this unique region as discussed in the reference below:

Latif, M., Martin, T., Reintges, A. et al. (2017) "Southern Ocean Decadal Variability and Predictability", Curr Clim Change Rep, doi:10.1007/s40641-017-0068-8

https://link.springer.com/article/10.1007%2Fs40641-017-0068-8?utm_content=bufferc013d&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "The Southern Ocean featured some remarkable changes during the recent decades. For example, large parts of the Southern Ocean, despite rapidly rising atmospheric greenhouse gas concentrations, depicted a surface cooling since the 1970s, whereas most of the planet has warmed considerably. In contrast, climate models generally simulate Southern Ocean surface warming when driven with observed historical radiative forcing. The mechanisms behind the surface cooling and other prominent changes in the Southern Ocean sector climate during the recent decades, such as expanding sea ice extent, abyssal warming, and CO2 uptake, are still under debate. Observational coverage is sparse, and records are short but rapidly growing, making the Southern Ocean climate system one of the least explored. It is thus difficult to separate current trends from underlying decadal to centennial scale variability. Here, we present the state of the discussion about some of the most perplexing decadal climate trends in the Southern Ocean during the recent decades along with possible mechanisms and contrast these with an internal mode of Southern Ocean variability present in state-of-the art climate models."

For Frey & Kay (2017) see:

William R. Frey & Jennifer E. Kay (2017), "The influence of extratropical cloud phase and amount feedbacks on climate sensitivity", Climate Dynamics; pp 1–20, doi:10.1007/s00382-017-3796-5
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on July 31, 2017, 03:07:12 AM
The linked reference indicates that new decadal-scale model projections for the Southern Ocean indicate that some component of the recent high levels of sea ice extents has been associated with weakening of the AABW cell in the Weddell Sea.  To me this weakening of this AABW cell supports Hansen's ice-climate feedback mechanism:

Zhang, Liping, Thomas L Delworth, Xiaosong Yang, Richard G Gudgel, Liwei Jia, Gabriel A Vecchi, and Fanrong Zeng, July 2017: Estimating decadal predictability for the Southern Ocean using the GFDL CM2.1 model. Journal of Climate, 30(14), DOI:10.1175/JCLI-D-16-0840.1

http://journals.ametsoc.org/doi/10.1175/JCLI-D-16-0840.1 (http://journals.ametsoc.org/doi/10.1175/JCLI-D-16-0840.1)

Abstract: “This study explores the potential predictability of the Southern Ocean (SO) climate on decadal time scales as represented in the GFDL CM2.1 model using prognostic methods. Perfect model predictability experiments are conducted starting from 10 different initial states, showing potentially predictable variations of Antarctic bottom water (AABW) formation rates on time scales as long as 20 years. The associated Weddell Sea (WS) subsurface temperatures and Antarctic sea ice have potential predictability comparable to that of the AABW cell. The predictability of sea surface temperature (SST) variations over the WS and the SO is somewhat smaller, with predictable scales out to a decade. This reduced predictability is likely associated with stronger damping from air–sea interaction. As a complement to this perfect predictability study, the authors also make hindcasts of SO decadal variability using the GFDL CM2.1 decadal prediction system. Significant predictive skill for SO SST on multiyear time scales is found in the hindcast system. The success of the hindcasts, especially in reproducing observed surface cooling trends, is largely due to initializing the state of the AABW cell. A weak state of the AABW cell leads to cooler surface conditions and more extensive sea ice. Although there are considerable uncertainties regarding the observational data used to initialize the hindcasts, the consistency between the perfect model experiments and the decadal hindcasts at least gives some indication as to where and to what extent skillful decadal SO forecasts might be possible.”
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 04, 2017, 01:17:12 AM
The linked reference finds that "... localized changes in coastal winds off East Antarctica can produce significant subsurface temperature anomalies (>2 °C) around much of the continent."

Paul Spence, Ryan M. Holmes, Andrew McC. Hogg, Stephen M. Griffies, Kial D. Stewart & Matthew H. England  (2017), "Localized rapid warming of West Antarctic subsurface waters by remote winds", Nature Climate Change, Volume: 7, Pages: 595–603, doi:10.1038/nclimate3335

http://www.nature.com/nclimate/journal/v7/n8/full/nclimate3335.html (http://www.nature.com/nclimate/journal/v7/n8/full/nclimate3335.html)

Abstract: "The highest rates of Antarctic glacial ice mass loss are occurring to the west of the Antarctica Peninsula in regions where warming of subsurface continental shelf waters is also largest. However, the physical mechanisms responsible for this warming remain unknown. Here we show how localized changes in coastal winds off East Antarctica can produce significant subsurface temperature anomalies (>2 °C) around much of the continent. We demonstrate how coastal-trapped barotropic Kelvin waves communicate the wind disturbance around the Antarctic coastline. The warming is focused on the western flank of the Antarctic Peninsula because the circulation induced by the coastal-trapped waves is intensified by the steep continental slope there, and because of the presence of pre-existing warm subsurface water offshore. The adjustment to the coastal-trapped waves shoals the subsurface isotherms and brings warm deep water upwards onto the continental shelf and closer to the coast. This result demonstrates the vulnerability of the West Antarctic region to a changing climate."

Edit, for an open access pdf see:


http://web.science.unsw.edu.au/~matthew/nclimate3335.pdf


Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 05, 2017, 03:57:55 AM
The linked open access reference helps to quantify the influence of the Equatorial Pacific on the Southern Ocean, and indicates that the variability of the Southern Ocean has significantly increased since the 1940's:

Turney, C. S. M., Fogwill, C. J., Palmer, J. G., van Sebille, E., Thomas, Z., McGlone, M., Richardson, S., Wilmshurst, J. M., Fenwick, P., Zunz, V., Goosse, H., Wilson, K.-J., Carter, L., Lipson, M., Jones, R. T., Harsch, M., Clark, G., Marzinelli, E., Rogers, T., Rainsley, E., Ciasto, L., Waterman, S., Thomas, E. R., and Visbeck, M.: Tropical forcing of increased Southern Ocean climate variability revealed by a 140-year subantarctic temperature reconstruction, Clim. Past, 13, 231-248, https://doi.org/10.5194/cp-13-231-2017, (https://doi.org/10.5194/cp-13-231-2017,) 2017.

https://www.clim-past.net/13/231/2017/ (https://www.clim-past.net/13/231/2017/)

Abstract: “Occupying about 14 % of the world's surface, the Southern Ocean plays a fundamental role in ocean and atmosphere circulation, carbon cycling and Antarctic ice-sheet dynamics. Unfortunately, high interannual variability and a dearth of instrumental observations before the 1950s limits our understanding of how marine–atmosphere–ice domains interact on multi-decadal timescales and the impact of anthropogenic forcing. Here we integrate climate-sensitive tree growth with ocean and atmospheric observations on southwest Pacific subantarctic islands that lie at the boundary of polar and subtropical climates (52–54° S). Our annually resolved temperature reconstruction captures regional change since the 1870s and demonstrates a significant increase in variability from the 1940s, a phenomenon predating the observational record. Climate reanalysis and modelling show a parallel change in tropical Pacific sea surface temperatures that generate an atmospheric Rossby wave train which propagates across a large part of the Southern Hemisphere during the austral spring and summer. Our results suggest that modern observed high interannual variability was established across the mid-twentieth century, and that the influence of contemporary equatorial Pacific temperatures may now be a permanent feature across the mid- to high latitudes.”
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 31, 2017, 06:36:26 PM
The linked reference discusses how global deep waters spiral to the surface of the Southern Ocean (see the attached image):

Tamsitt V, Drake HF, Morrison AK, et al. (2017), "Spiraling Pathways of Global Deep Waters to the Surface of the Southern Ocean." Nature Communications.;8:172, DOI: 10.1038/s41467-017-00197-0

https://www.nature.com/articles/s41467-017-00197-0 (https://www.nature.com/articles/s41467-017-00197-0)

Abstract: "Upwelling of global deep waters to the sea surface in the Southern Ocean closes the global overturning circulation and is fundamentally important for oceanic uptake of carbon and heat, nutrient resupply for sustaining oceanic biological production, and the melt rate of ice shelves. However, the exact pathways and role of topography in Southern Ocean upwelling remain largely unknown. Here we show detailed upwelling pathways in three dimensions, using hydrographic observations and particle tracking in high-resolution models. The analysis reveals that the northern-sourced deep waters enter the Antarctic Circumpolar Current via southward flow along the boundaries of the three ocean basins, before spiraling southeastward and upward through the Antarctic Circumpolar Current. Upwelling is greatly enhanced at five major topographic features, associated with vigorous mesoscale eddy activity. Deep water reaches the upper ocean predominantly south of the Antarctic Circumpolar Current, with a spatially nonuniform distribution. The timescale for half of the deep water to upwell from 30° S to the mixed layer is ~60–90 years."

Caption for attached image: "The three dimensional upward spiral of North Atlantic Deep Water through the Southern Ocean. a Observed warm water (>1.6 °C) on the 28.05 kg m−3 neutral density surface from hydrographic observations27, south of 40° S, colored by depth (m). The isoneutral surface is masked in regions with potential temperature below 1.6 °C. 1/4° ocean bathymetry70 is shown in gray. b Modeled (CM2.6) particle pathways from the Atlantic Ocean, with particles released in the depth range 1000–3500 m along 30° S. Colored boxes mark 1° latitude × 1° longitude × 100 m depth grid boxes visited by >3.5% of the total upwelling particle-transport from release at 30° S to the mixed layer. Boxes are colored by depth, similar to a. c Two example upwelling particle trajectories from CM2.6, one originating from the western Atlantic and the other from the eastern Atlantic. Trajectories are colored by depth as in a and b, blue spheres show the particle release locations and red spheres show the location where the particles reach the mixed layer. Three-dimensional maps were produced using Python and Mayavi"
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on September 17, 2017, 11:05:26 AM
Interesting information on the correlation of ozone depletion over Antarctica and the Southern Annular Mode (SAM):

Jiao Yang & Cunde Xiao (15 September 2017), "The evolution and volcanic forcing of the southern annular mode during the past 300 years", International Journal of Climatology, DOI: 10.1002/joc.5290 

http://onlinelibrary.wiley.com/doi/10.1002/joc.5290/abstract?utm_content=buffer77291&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer (http://onlinelibrary.wiley.com/doi/10.1002/joc.5290/abstract?utm_content=buffer77291&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer)

Extract: "A positive change in the southern annular mode (SAM), which is the primary pattern of climate variability in the Southern Hemisphere, has been induced predominantly by polar stratospheric ozone depletion. However, the lack of long-term observational records limits our understanding of the long-term SAM behaviour. In this study, we found that the geochemical record of the LGB69 ice core from the eastern coast of Antarctica was significantly correlated with the winter SAM index (SAMI). In addition, we developed an annual mean SAMI beginning in 1701 based on 15 annually resolved ice cores and relevant proxy–climate relationships. Our reconstruction accounted for 54.8% of the total variance from 1957 to 2000 (the calibration period). We demonstrate that the recent positive phase shift in the annual mean SAMI since the 1970s is unprecedented, with the estimate for the latest regime in the 1990s reaching values 2.5 times the standard deviation above the baseline (1701–2000). This peak value also coincides with the largest 30- and 50-year trends, which have occurred at the end of the 20th century. From the reconstructed SAMI, we also found that the response to large volcanic events was likely positive in the 3 years after the eruption, but this positive response can be masked by internal climate variability when a strong El Niño event occurs in the eruption year."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: solartim27 on September 19, 2017, 09:02:34 PM
Quote
A NASA study has located the Antarctic glaciers that accelerated the fastest between 2008 and 2014 and finds that the most likely cause of their speedup is an observed influx of warm water into the bay where they're located.

The water was only 1 to 2 degrees Fahrenheit (0.5 to 1 degree Celsius) warmer than usual water temperatures in the area, but it increased the glaciers' flow speeds by up to 25 percent and multiplied the rate of glacial ice loss by three to five times -- from 7 to 10 feet of thinning per year (2 to 3 meters) up to 33 feet per year (10 meters).

https://www.jpl.nasa.gov/news/news.php?feature=6949 (https://www.jpl.nasa.gov/news/news.php?feature=6949)
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on September 30, 2017, 06:43:41 PM
The linked reference used climate models that include eddies in the ocean to confirm many of the ice-climate feedback mechanisms cited by Hansen.  Hopefully, CMIP6 models will benefit these lessons:

Paul B. Goddard, Carolina O. Dufour, Jianjun Yin, Stephen M. Griffies & Michael Winton (17 September 2017), "CO2-Induced Ocean Warming of the Antarctic Continental Shelf in an Eddying Global Climate Model", JGR Oceans, DOI: 10.1002/2017JC012849

http://onlinelibrary.wiley.com/doi/10.1002/2017JC012849/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2017JC012849/abstract)

Abstract: "Ocean warming near the Antarctic ice shelves has critical implications for future ice sheet mass loss and global sea level rise. A global climate model with an eddying ocean is used to quantify the mechanisms contributing to ocean warming on the Antarctic continental shelf in an idealized 2xCO2 experiment. The results indicate that relatively large warm anomalies occur both in the upper 100 m and at depths above the shelf floor, which are controlled by different mechanisms. The near-surface ocean warming is primarily a response to enhanced onshore advective heat transport across the shelf break. The deep shelf warming is initiated by onshore intrusions of relatively warm Circumpolar Deep Water (CDW), in density classes that access the shelf, as well as the reduction of the vertical mixing of heat. CO2-induced shelf freshening influences both warming mechanisms. The shelf freshening slows vertical mixing by limiting gravitational instabilities and the upward diffusion of heat associated with CDW, resulting in the build-up of heat at depth. Meanwhile, freshening near the shelf break enhances the lateral density gradient of the Antarctic Slope Front (ASF) and disconnect isopycnals between the shelf and CDW, making cross-ASF heat exchange more difficult. However, at several locations along the ASF, the cross-ASF heat transport is less inhibited and heat can move onshore. Once onshore, lateral and vertical heat advection work to disperse the heat anomalies across the shelf region. Understanding the inhomogeneous Antarctic shelf warming will lead to better projections of future ice sheet mass loss."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on October 12, 2017, 02:54:05 PM
The linked reference highlights how counterproductive the current glacial models are when they estimate that the Dotson Ice Shelf would not collapse for another 250 years when due to oceanic melting it might collapse within 40 to 50 years, and if hydrofracturing occurs it might collapse 25 to 30 years.

Noel Gourmelen et al (2017), "Channelized Melting Drives Thinning Under a Rapidly Melting Antarctic Ice Shelf", Geophysical Research Letters, DOI: 10.1002/2017GL074929 

http://onlinelibrary.wiley.com/doi/10.1002/2017GL074929/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2017GL074929/abstract)

Abstract: "Ice shelves play a vital role in regulating loss of grounded ice and in supplying freshwater to coastal seas. However, melt variability within ice shelves is poorly constrained and may be instrumental in driving ice shelf imbalance and collapse. High-resolution altimetry measurements from 2010 to 2016 show that Dotson Ice Shelf (DIS), West Antarctica, thins in response to basal melting focused along a single 5 km-wide and 60 km-long channel extending from the ice shelf's grounding zone to its calving front. If focused thinning continues at present rates, the channel will melt through, and the ice shelf collapse, within 40–50 years, almost two centuries before collapse is projected from the average thinning rate. Our findings provide evidence of basal melt-driven sub-ice shelf channel formation and its potential for accelerating the weakening of ice shelves."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on October 12, 2017, 03:02:02 PM
The linked article explores the relationship between the Antarctic Ozone hole and sea ice extent.  To me the results indicate that our current models are not adequate to simulate the complexities of the Southern Ocean and Antarctica subjected to anthropogenic forcing:

Laura Landrum, Marika Holland, Marilyn Raphael & Lorenzo Polvani (11 October 2017), "Stratospheric ozone depletion: an unlikely driver of the regional trends in Antarctic sea ice in austral fall in the late 20th Century", Geophysical Research Letters, DOI: 10.1002/2017GL075618 

http://onlinelibrary.wiley.com/doi/10.1002/2017GL075618/abstract?utm_content=bufferbf6ea&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer (http://onlinelibrary.wiley.com/doi/10.1002/2017GL075618/abstract?utm_content=bufferbf6ea&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer)

Abstract: "It has been suggested that recent regional trends in Antarctic sea ice might have been caused by the formation of the ozone hole in the late 20th century. Here we explore this by examining two ensembles of a climate model over the ozone hole formation period (1955-2005). One ensemble includes all known historical forcings; the other is identical except for ozone levels, which are fixed at 1955 levels. We demonstrate that the model is able to capture, on interannual and decadal time scales, the observed statistical relationship between summer Amundsen Sea Low strength (when ozone loss causes a robust deepening) and fall sea-ice concentrations (when observed trends are largest). In spite of this, the modeled regional trends caused by ozone depletion are found to be almost exactly opposite to the observed ones. We deduce that the regional character of observed sea ice trends is likely not caused by ozone depletion."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on October 15, 2017, 04:59:00 PM
CMIP5 did not include freshwater hosing from Antarctic ice mass loss to the ocean and thus produced projections of Antarctic sea ice that correlated poorly with the observations from 1980 to 2013.  However, when the linked reference included this freshwater hosing into CESM1(CAM5) they found much improved correlation:

Andrew G. Pauling, Inga J. Smith, Patricia J. Langhorne & Cecilia M. Bitz (9 October 2017), "Time-dependent freshwater input from ice shelves: impacts on Antarctic sea ice and the Southern Ocean in an Earth System Model", Geophysical Research Letters, DOI: 10.1002/2017GL075017 

http://onlinelibrary.wiley.com/doi/10.1002/2017GL075017/abstract?utm_content=buffer0aa71&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer (http://onlinelibrary.wiley.com/doi/10.1002/2017GL075017/abstract?utm_content=buffer0aa71&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer)

Abstract: "Earth System Models do not reproduce the observed increase in Antarctic sea ice extent which may be due to the unrealistic representation of ice shelves. Here we investigate the response of sea ice to increasing freshwater input from ice shelves using the Community Earth System Model with the Community Atmosphere Model version 5 [CESM1(CAM5)]. Including the effect of heat loss from the ocean to melt ice shelves resulted in significantly more positive trends in sea ice area. We have conducted model experiments adding fresh water as if from ice shelf melt with a linear increase in the rate of input over the period 1980-2013. We found that an increase in the rate of change of freshwater input of ∼45 Gt yr−2 was sufficient to offset the negative trend in sea ice area in CESM1(CAM5), although the freshwater input by the end of the experiment was larger than observed at that time."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on November 10, 2017, 05:39:29 PM
The linked reference provides an update on progress being made on modeling the complex Southern Ocean- Antarctic Ice Sheet interaction:

Asay-Davis, X.S., Jourdain, N.C. & Nakayama, Y. (2017), "Developments in Simulating and Parameterizing Interactions Between the Southern Ocean and the Antarctic Ice Sheet", Curr Clim Change Rep, https://doi.org/10.1007/s40641-017-0071-0

https://link.springer.com/article/10.1007%2Fs40641-017-0071-0

Abstract: "Recent advances in both ocean modeling and melt parameterization in ice-sheet models point the way toward coupled ice sheet–ocean modeling, which is needed to quantify Antarctic mass loss and the resulting sea-level rise. The latest Antarctic ocean modeling shows that complex interactions between the atmosphere, sea ice, icebergs, bathymetric features, and ocean circulation on many scales determine which water masses reach ice-shelf cavities and how much heat is available to melt ice. Meanwhile, parameterizations of basal melting in standalone ice-sheet models have evolved from simplified, depth-dependent functions to more sophisticated models, accounting for ice-shelf basal topography, and the evolution of the sub-ice-shelf buoyant flow. The focus of recent work has been on better understanding processes or adding new model capabilities, but a broader community effort is needed in validating models against observations and producing melt-rate projections. Given time, community efforts in coupled ice sheet–ocean modeling, already underway, will tackle the considerable challenges involved in building, initializing, constraining, and performing projections with coupled models, leading to reduced uncertainties in Antarctica’s contribution to future sea-level rise."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on November 26, 2017, 06:23:18 PM
Current ESMs do not model either aerosols and/or aerosol cloud interactions very well in the Southern Ocean and Antarctica.  The two linked (& related) references provides new information about paleo aerosols over central Antarctica based on ice cores.  Hopefully, such information can be used to reduce the bias of current ESMs projections with regard to the climate response to warming in the high latitudes of the SH:

Legrand, M., Preunkert, S., Wolff, E., Weller, R., Jourdain, B., and Wagenbach, D.: Year-round records of bulk and size-segregated aerosol composition in central Antarctica (Concordia site) – Part 1: Fractionation of sea-salt particles, Atmos. Chem. Phys., 17, 14039-14054, https://doi.org/10.5194/acp-17-14039-2017, 2017.

https://www.atmos-chem-phys.net/17/14039/2017/

Abstract. Multiple year-round records of bulk and size-segregated composition of aerosol were obtained at the inland site of Concordia located at Dome C in East Antarctica. In parallel, sampling of acidic gases on denuder tubes was carried out to quantify the concentrations of HCl and HNO3 present in the gas phase. These time series are used to examine aerosol present over central Antarctica in terms of chloride depletion relative to sodium with respect to freshly emitted sea-salt aerosol as well as depletion of sulfate relative to sodium with respect to the composition of seawater. A depletion of chloride relative to sodium is observed over most of the year, reaching a maximum of  ∼ 20 ng m−3 in spring when there are still large sea-salt amounts and acidic components start to recover. The role of acidic sulfur aerosol and nitric acid in replacing chloride from sea-salt particles is here discussed. HCl is found to be around twice more abundant than the amount of chloride lost by sea-salt aerosol, suggesting that either HCl is more efficiently transported to Concordia than sea-salt aerosol or re-emission from the snow pack over the Antarctic plateau represents an additional significant HCl source. The size-segregated composition of aerosol collected in winter (from 2006 to 2011) indicates a mean sulfate to sodium ratio of sea-salt aerosol present over central Antarctica of 0.16 ± 0.05, suggesting that, on average, the sea-ice and open-ocean emissions equally contribute to sea-salt aerosol load of the inland Antarctic atmosphere. The temporal variability of the sulfate depletion relative to sodium was examined at the light of air mass backward trajectories, showing an overall decreasing trend of the ratio (i.e., a stronger sulfate depletion relative to sodium) when air masses arriving at Dome C had traveled a longer time over sea ice than over open ocean. The findings are shown to be useful to discuss sea-salt ice records extracted at deep drilling sites located inland Antarctica.

&

Legrand, M., Preunkert, S., Weller, R., Zipf, L., Elsässer, C., Merchel, S., Rugel, G., and Wagenbach, D.: Year-round record of bulk and size-segregated aerosol composition in central Antarctica (Concordia site) – Part 2: Biogenic sulfur (sulfate and methanesulfonate) aerosol, Atmos. Chem. Phys., 17, 14055-14073, https://doi.org/10.5194/acp-17-14055-2017, 2017.

https://www.atmos-chem-phys.net/17/14055/2017/

Abstract. Multiple year-round (2006–2015) records of the bulk and size-segregated composition of aerosol were obtained at the inland site of Concordia located in East Antarctica. The well-marked maximum of non-sea-salt sulfate (nssSO4) in January (100 ± 28 ng m−3 versus 4.4 ± 2.3 ng m−3 in July) is consistent with observations made at the coast (280 ± 78 ng m−3 in January versus 16 ± 9 ng m−3 in July at Dumont d'Urville, for instance). In contrast, the well-marked maximum of MSA at the coast in January (60 ± 23 ng m−3 at Dumont d'Urville) is not observed at Concordia (5.2 ± 2.0 ng m−3 in January). Instead, the MSA level at Concordia peaks in October (5.6 ± 1.9 ng m−3) and March (14.9 ± 5.7 ng m−3). As a result, a surprisingly low MSA-to-nssSO4 ratio (RMSA) is observed at Concordia in mid-summer (0.05 ± 0.02 in January versus 0.25 ± 0.09 in March). We find that the low value of RMSA in mid-summer at Concordia is mainly driven by a drop of MSA levels that takes place in submicron aerosol (0.3 µm diameter). The drop of MSA coincides with periods of high photochemical activity as indicated by high ozone levels, strongly suggesting the occurrence of an efficient chemical destruction of MSA over the Antarctic plateau in mid-summer. The relationship between MSA and nssSO4 levels is examined separately for each season and indicates that concentration of non-biogenic sulfate over the Antarctic plateau does not exceed 1 ng m−3 in fall and winter and remains close to 5 ng m−3 in spring. This weak non-biogenic sulfate level is discussed in the light of radionuclides (210Pb, 10Be, and 7Be) also measured on bulk aerosol samples collected at Concordia. The findings highlight the complexity in using MSA in deep ice cores extracted from inland Antarctica as a proxy of past dimethyl sulfide emissions from the Southern Ocean.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on March 14, 2018, 05:18:19 PM
The linked reference cites model output that indicates: "… that isopycnal eddy stirring is the principal mechanism of shoreward heat transport around Antarctica, though likely modulated by tides and surface forcing."

Andrew L. Stewart, Andreas Klocker & Dimitris Menemenlis (19 January 2018), "Circum-Antarctic Shoreward Heat Transport Derived From an Eddy- and Tide-Resolving Simulation", Geophysical Research Letters, DOI: 10.1002/2017GL075677

http://onlinelibrary.wiley.com/doi/10.1002/2017GL075677/full

Extract: "Almost all heat reaching the bases of Antarctica's ice shelves originates from warm Circumpolar Deep Water in the open Southern Ocean. This study quantifies the roles of mean and transient flows in transporting heat across almost the entire Antarctic continental slope and shelf using an ocean/sea ice model run at eddy- and tide-resolving (1/48°) horizontal resolution. Heat transfer by transient flows is approximately attributed to eddies and tides via a decomposition into time scales shorter than and longer than 1 day, respectively. It is shown that eddies transfer heat across the continental slope (ocean depths greater than 1,500 m), but tides produce a stronger shoreward heat flux across the shelf break (ocean depths between 500 m and 1,000 m). However, the tidal heat fluxes are approximately compensated by mean flows, leaving the eddy heat flux to balance the net shoreward heat transport. The eddy-driven cross-slope overturning circulation is too weak to account for the eddy heat flux. This suggests that isopycnal eddy stirring is the principal mechanism of shoreward heat transport around Antarctica, though likely modulated by tides and surface forcing."
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: aperson on June 14, 2018, 09:27:14 AM
Antarctic SIE predictions on multi-yearly time scales

Marchi, S., Fichefet, T., Goosse, H. et al. Clim Dyn (14 June 2018)., Reemergence of Antarctic sea ice predictability and its link to deep ocean mixing in global climate models, https://doi.org/10.1007/s0038

Quote
"This first multi-model study of Antarctic sea ice predictability reveals that the ice edge location can potentially be predicted up to 3 years in advance. However, the ice edge location predictability shows contrasted seasonal performances, with high predictability in winter and no predictability in summer. The reemergence of the predictability from one winter to next is provided by the ocean through its large thermal inertia. Sea surface heat anomalies are stored at depth at the end of the winter and influences the sea ice advance the following year as they resurface. The effectiveness of this mechanism across models is found to depend upon the depth of the mixed layer."

If we want to understand forecasting Antarctic Sea Ice, we should be looking at the ocean in winter.
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: morganism on August 12, 2018, 01:49:37 AM
Holocene warming effect of southern ocean

"Because of the enhanced Southern Ocean upwelling, the biological pump weakened over the Holocene, allowing more carbon dioxide to leak from the deep ocean into the atmosphere and thus possibly explaining the 20 ppm rise in atmospheric carbon dioxide.

“This process is allowing some of that deeply stored carbon dioxide to invade back to the atmosphere,” said Sigman. “We’re essentially punching holes in the membrane of the biological pump.”

https://www.astrobio.net/alien-life/carbon-leak-may-have-warmed-the-planet-for-11000-years-encouraging-human-civilization/
Title: Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
Post by: AbruptSLR on August 12, 2018, 04:07:44 AM
Holocene warming effect of southern ocean

"Because of the enhanced Southern Ocean upwelling, the biological pump weakened over the Holocene, allowing more carbon dioxide to leak from the deep ocean into the atmosphere and thus possibly explaining the 20 ppm rise in atmospheric carbon dioxide.

“This process is allowing some of that deeply stored carbon dioxide to invade back to the atmosphere,” said Sigman. “We’re essentially punching holes in the membrane of the biological pump.”

https://www.astrobio.net/alien-life/carbon-leak-may-have-warmed-the-planet-for-11000-years-encouraging-human-civilization/

Newly identified evidence indicates that the Southern Ocean will likely stop absorbing as much CO₂ as it recently has been doing, with continuing anthropogenic radiative forcing:

Title: "How much longer will Southern Ocean slow climate change?"

http://www.newstalkzb.co.nz/news/national/how-much-longer-will-southern-ocean-slow-climate-change/

Extract: "The vast and wild ocean current sucks up more than 40 per cent of the carbon dioxide we produce, acting as a temporary climate-change buffer by slowing down the accumulation of greenhouse gases in our atmosphere.

Yet the same westerly winds that play a critical role in regulating its storing capacity are now threatening its future as a CO2 bank, by bringing deep carbon-rich waters up to the surface.
Many climate models predict that the westerly winds overlying the ocean would get stronger if atmospheric greenhouse gas concentrations continued to risk.

A new international study suggests that in the past, strong westerlies have been linked to higher levels of atmospheric CO2 due to their impact on the Southern Ocean carbon balance.

That meant stronger westerlies could actually speed up climate change if mankind continued to emit as much CO2 as it does today.

"Our new records of the Southern Hemisphere westerly winds suggest there have been large changes in wind intensity over the past 12,000 years.

"This is in marked contrast to climate model simulations that predict only relatively small wind speed changes over the same period."

Yet, Mikaloff-Fletcher added, sea surface carbon data suggested that there was a reversal of this trend in the early 2000s, when the Southern Ocean began taking up carbon much more quickly, even though the westerlies didn't slow.

"The mechanisms behind this change still aren't fully explained, which makes it hard to predict whether this is a short-term effect or a long-term one," she said.

"The Macquarie study suggests that the sudden increase in Southern Ocean carbon uptake may not persist on longer timescales.""