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Author Topic: Thermohaline Circulation Connections  (Read 5834 times)


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Thermohaline Circulation Connections
« on: November 30, 2015, 09:08:51 PM »
I apologize for posing both two newbie questions and a newbie hypothesis in a post, but I hope you good folks will bear with me.

Question 1: to what extent is the global THC connected to itself?  Given the ~1000 year transit time, does it matter in the timeframes in which we're concerned about?  Does the apparent slowing of the AMOC also imply a slowing of other components of the global circulation system?  If so, then:

Hypothesis: the Blob is the counterpart to the North Atlantic Drift disturbance. If the entire global THC is slowing down, not just the AMOC, then reduced upwelling of cold waters off the Pacific Coast could very much explain the Blob, and I would not expect the Blob to go away until the North Atlantic cold spot goes away as well.

Question 2: Is there any mechanism by which a vigorously evolving El Nino could buttress the cold, deep flow across the equator, allowing the Blob to diminish in magnitude temporarily?  This would imply a direct, causal relationship between the temporary weakening of the Blob and El Nino rather than the co-incidental relationship most presume today.  The dissipation pattern the Blob had been exhibiting seemed to me much more radiative than convective, which would be consistent with increased upwelling and natural conductive and radiative heat transfer.

This seems like a really obvious thing to investigate and I know there are a lot of data series such as upwelling indices, but I don't have the depth in the field to interpret them properly and I can't find this presented as a body of research.  Does someone know anywhere the questions have been seriously addressed?  I would love to read their insights.

If there is any connection here, then the reduction in salinity from the increased river flow, arctic ice melting, Greenland, etc. that may be disrupting the currents of the North Atlantic may be ultimately responsible for the Blob too.

The other thing I wonder about is whether the total amount of first year ice that gets converted to multi-year ice affects how much salinity is input during the winter.  If we get deeper freeze/melt cycles, would we expect much stronger annual fluctuations in salinity in the North Atlantic?  Just weaker because it's the minimum extent that matters for brine rejection?  Would any effect be large enough to even consider?

Thank you for taking the time to read my thoughts.  I'll try to gradually lurk less as I learn more, but I'm obviously still in the neophyte stage here.
« Last Edit: December 01, 2015, 07:13:52 PM by Okono »


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Re: Thermohaline Circulation Connections
« Reply #1 on: December 28, 2015, 12:17:54 PM »
Let me add a testable hypothesis to this.  I believe that, as the atmospheric and oceanic forces that bolstered El Nino begin to run in reverse, the Blob should rapidly regrow.  This is in contrast to the CFSv2 model, which currently forecasts a normalization in sea surface temperatures except near the coast.

Give it six months, and wish me luck.

Bruce Steele

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Re: Thermohaline Circulation Connections
« Reply #2 on: December 29, 2015, 12:07:57 AM »
Okono, You can think of the ocean as a large layer cake with surface water circulation as well as intermediate water, deep water and bottom water processes all operating at different timeframes. The different layers are separated by salinity and temperature differences . Surface waters move relatively quickly with intermediate waters moving slower , crossing the Pacific in 35-50 years ,for instance.
Deep water processes move slower still with circulation in the thousand year timeframe in MOC waters from their downwelling in the North Atlantic to their eventual upwelling in the equatorial Eastern Pacific. The North Pacific has no areas that produce deep or bottom water and as a result have some of the oldest deep ocean waters on earth. So MOC slowing processes in the Atlantic have no ability for teleconnection with the North Pacific surface waters without many many years in time lag. There may be atmospheric connections however and the deep ridging taking place in the Pacific and Atlantic may have common drivers.
 The large and persistent high pressure ridging in the North Pacific has deflected low pressure storm systems and as a result surface water mixing has decreased allowing surface water temperatures to increase. This is a positive reinforcing mechanism as the warm surface waters add strength to the stable high pressure system.
 The Kuroshio current crosses the Pacific from Japan to North America and splits as it encounters the north American continent then forming the Calif.Current headed south and the Alaskan Gyre headed north. During the warm phase of the PDO more of the Kuroshio is deflected north so it may be the last two + years of positive PDO index conditions is also playing a role in formation of "the blob."
 If you would like to delve deeper into MOC processes I would recommend reading "The Great Ocean Conveyer" by Wally Broecker.
 Questions about how the changes in North Atlantic MOC processes and the subsequent cold surface waters might telecommunicate via the atmosphere to the equally anomalous North Pacific warm water blob is an interesting thing to ponder.
I am personally hoping the El Nino takes over and allows some storms to make it down here into Southern Calif.  If some strong storms move through surface mixing should break down " the blob " at least for awhile. Should know within the next two weeks.           
« Last Edit: December 29, 2015, 03:59:44 AM by Bruce Steele »


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Re: Thermohaline Circulation Connections
« Reply #3 on: December 31, 2015, 02:41:19 AM »
hoping the El Nino takes over and allows some storms into Southern Calif.  If some strong storms move through surface mixing should break down " the blob " at least for awhile. Should know within the next two weeks.   
Southern California and the southern tier remain in the grip of a strong La Nada (non-technical sense) for the foreseeable future (next 10 days). El Nino events contribute only ~7% overall of long-term CA precip anyway. SoCal has very little surface or groundwater storage capability. (Subsidence over clay is irreversible.) The Colorado River upper basin snowpack is unexceptional at 114% of the December 30th average. The lower Colorado share will largely go to alfalfa, though not water rights for the 29000 acres Metro just bought from the Mormon Church in Blythe.

30 Dec 15 NWS Scientific Forecaster Discussion ... models seem to have locked into their respective biases for next week's series of troughs but with significant differences early on. The GFS is  still showing the initial system coming in late Sunday and Monday  while the European model (ecmwf)/Gem solutions are taking it much farther south... much higher confidence for rain during this  time frame than on Monday. However amounts are still very uncertain.

Precipitable waters are generally under an inch for the duration of the event and  all the various parameters (moisture, temperatures, wind) are all within 2 std dev of normal so from that standpoint it doesn't look like anything more than a slightly above normal winter  storm event.  It seems likely seasonal rainfall totals will still be 20-30% below  normal by the time the last of the rain has ended next week.

If this means 'rainfall totals will still be 20-30% below normal for the Jan 8th date', some would call this continuing drought. I really must remember to take screenshots of NWS SFDs. They had a hilarious one a few hours ago -- now gone -- kinda attributing this storm system to El Nino as the pattern was sorta like one. Until it wasn't.

Bruce Steele

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Re: Thermohaline Circulation Connections
« Reply #4 on: December 31, 2015, 07:43:46 PM »
Maybe it's a little premature to call " the blob " dead but SST's for the waters off Northern Calif. Oregon and Washington have returned to something closer to normal as reflected in the drop in the PDO index for Nov. and ( guessing here ) probably Dec.  The water temperature in Southern Calif. has dropped a lot lately as well.
 Here is the SST anomaly

I think the 7% average precipitation contribution to overall total   for El Nino events may not be the same as I would expect from a Super El Nino. 82-83 big rain, 97-98 big rain 16-17 ?.  That said ,we are still in a drought !  I would agree the population centers do not have adequate groundwater supplies and Lake Cahuma ( the major supplier of Santa Barbara supplies ) is at 15% and dropping. Reflective of similar
stories in other areas of the state. If this drought continues or gets worse .... I don't
wanna go's gotta rain.
 Sierra Snowpack is above average for the first time in several years and there are several storms in the forecast that will dump more over the next couple weeks . Maybe if we got that doubled by March our California reservoirs will get some storage built. Our local reservoirs need rain to refill but things do look better in Northern Calif.  I am hoping for a  200% Sierra Snowpack but it is a two edged sword , it may refill reservoirs but if it were to melt quickly it could also cause some nasty flooding.
 I am headed to get some rain gutters today so I'm putting my money on rain. Lot's.     


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Re: Thermohaline Circulation Connections
« Reply #5 on: September 19, 2019, 02:17:35 AM »
"A key question for climate scientists in recent years has been whether the Atlantic Ocean's main circulation system is slowing down, a development that could have dramatic consequences for Europe and other parts of the Atlantic rim. But a new study suggests help may be on the way from an unexpected source -- the Indian Ocean.
Think of it as ocean-to-ocean altruism in the age of climate change.
The new study, from Shineng Hu of the Scripps Institution of Oceanography at the University of California-San Diego and Alexey Fedorov of Yale University, appears Sept. 16 in the journal Nature Climate Change. It is the latest in a growing body of research that explores how global warming may alter global climate components such as the Atlantic meridional overturning circulation (AMOC).
AMOC is one of the planet's largest water circulation systems. It operates like a liquid escalator, delivering warm water to the North Atlantic via an upper limb and sending colder water south via a deeper limb.
Although AMOC has been stable for thousands of years, data from the past 15 years, as well as computer model projections, have given some scientists cause for concern. AMOC has showed signs of slowing during that period, but whether it is a result of global warming or only a short-term anomaly related to natural ocean variability is not known.
"There is no consensus yet," Fedorov said, "but I think the issue of AMOC stability should not be ignored. The mere possibility that the AMOC could collapse should be a strong reason for concern in an era when human activity is forcing significant changes to the Earth's systems.
"We know that the last time AMOC weakened substantially was 15,000 to 17,000 years ago, and it had global impacts," Fedorov added. "We would be talking about harsh winters in Europe, with more storms or a drier Sahel in Africa due to the downward shift of the tropical rain belt, for example."
Much of Fedorov and Hu's work focuses on specific climate mechanisms and features that may be shifting due to global warming. Using a combination of observational data and sophisticated computer modeling, they plot out what effects such shifts might have over time. For example, Fedorov has looked previously at the role melting Arctic sea ice might have on AMOC.
For the new study, they looked at warming in the Indian Ocean.
"The Indian Ocean is one of the fingerprints of global warming," said Hu, who is first author of the new work. "Warming of the Indian Ocean is considered one of the most robust aspects of global warming."
The researchers said their modeling indicates a series of cascading effects that stretch from the Indian Ocean all way over to the Atlantic: As the Indian Ocean warms faster and faster, it generates additional precipitation. This, in turn, draws more air from other parts of the world, including the Atlantic, to the Indian Ocean.
With so much precipitation in the Indian Ocean, there will be less precipitation in the Atlantic Ocean, the researchers said. Less precipitation will lead to higher salinity in the waters of the tropical portion of the Atlantic -- because there won't be as much rainwater to dilute it. This saltier water in the Atlantic, as it comes north via AMOC, will get cold much quicker than usual and sink faster.
"This would act as a jump-start for AMOC, intensifying the circulation," Fedorov said. "On the other hand, we don't know how long this enhanced Indian Ocean warming will continue. If other tropical oceans' warming, especially the Pacific, catches up with the Indian Ocean, the advantage for AMOC will stop."
The researchers said this latest finding illustrates the intricate, interconnected nature of global climate. As scientists try to understand the unfolding effects of climate change, they must attempt to identify all of the climate variables and mechanisms that are likely to play a role, they added.
"There are undoubtedly many other connections that we don't know about yet," Fedorov said. "Which mechanisms are most dominant? We're interested in that interplay.""


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Re: Thermohaline Circulation Connections
« Reply #6 on: August 08, 2020, 12:30:47 AM »
Florida Current is Weaker Now Than at Any Point in the Past Century

"Piecuch, who specializes in coastal and regional sea level change, used a connection between coastal sea level and the strength of near-shore currents to trace the evolution of the Florida Current, which forms the beginning of the Gulf Stream. "

Nature Communications published on August 7


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Re: Thermohaline Circulation Connections
« Reply #7 on: August 08, 2020, 12:37:40 AM »
^ Related ...

Florida Current Weaker Now Than At Any Point In the Past Century

A key component of the Gulf Stream has markedly slowed over the past century—that's the conclusion of a new research paper in Nature Communications published on August 7.

Weakening of the Florida Current transport is apparent on longer timescales. The centennial trend during 1909–2018 is  −1.7 ± 3.7 Sv century−1, which overlaps zero, but implies that the trend is likely negative (P = 0.82; Supplementary Fig. 3b).

Christopher G. Piecuch, Likely weakening of the Florida Current during the past century revealed by sea-level observations, Nature Communications (2020)
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Re: Thermohaline Circulation Connections
« Reply #8 on: August 08, 2020, 02:44:08 PM »
From the study.
Yeah, likely to shut down in the 4th millenium