Please support this Forum and Neven's Blog

Author Topic: Risks and Challenges for Regional Circulation Models of the Southern Ocean  (Read 50785 times)

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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."
« Last Edit: May 06, 2013, 02:48:28 AM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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.”
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Bruce Steele

  • ASIF Upper Class
  • Posts: 1045
    • View Profile
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 .         

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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.
« Last Edit: May 06, 2013, 05:04:37 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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
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
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
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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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.
« Last Edit: May 09, 2013, 03:42:40 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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).
« Last Edit: May 09, 2013, 04:38:02 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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, 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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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.
« Last Edit: May 09, 2013, 10:12:53 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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
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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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/; 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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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

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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
The following information comes from an article that can be downloaded from:

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).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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/; doi:10.5194/tc-7-303-2013

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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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/

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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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.

« Last Edit: July 10, 2013, 07:48:14 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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

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

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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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

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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
The linked reference indicates the risks and challenges of modeling the Southern Ocean:

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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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

 
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


"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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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/; doi:10.5194/gmd-6-1209-2013

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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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

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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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


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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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


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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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

“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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


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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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

 
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



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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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


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


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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
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


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-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)."

“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #42 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


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


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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #43 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


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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #44 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

 
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

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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #45 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

 
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


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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #46 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

(see also:  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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #47 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

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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #48 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

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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12774
    • View Profile
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #49 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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson