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bbr2314

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Re: AMOC slowdown
« Reply #50 on: May 29, 2018, 06:14:58 PM »
Yesterdays article by Ramstorf.
http://www.realclimate.org/index.php/archives/2018/05/if-you-doubt-that-the-amoc-has-weakened-read-this/
In the comments Ramsdorf seems to dismiss Greenland melt's impacts.... I would say that is quite incorrect...

sidd

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Re: AMOC slowdown
« Reply #51 on: May 29, 2018, 06:29:53 PM »
In the response he indicated that melt has impact on surface salinity but not on largescale temperature.

"[Response: You mean by cold meltwater from Greenland flowing in? You can work that out from a simple heat budget calculation. The amount is far too small to matter for the large-scale sea surface temperature, but enough to matter for sea surface salinity. -Stefan] "

I did a simple heat calculation, and i agree with him.

sidd

bbr2314

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Re: AMOC slowdown
« Reply #52 on: May 29, 2018, 06:32:49 PM »
In the response he indicated that melt has impact on surface salinity but not on largescale temperature.

"[Response: You mean by cold meltwater from Greenland flowing in? You can work that out from a simple heat budget calculation. The amount is far too small to matter for the large-scale sea surface temperature, but enough to matter for sea surface salinity. -Stefan] "

I did a simple heat calculation, and i agree with him.

sidd
What about snowmelt from adjacent areas in North America as well? I think a look at recent evolving SSTAs shows this is indeed a major factor...

I would also add that contrary to his research, you can see the pulse of high heights begin to rise off the East Coast of North America in July / August / September rather than in wintertime (each and every year, most recently). Again, this supports a greater relationship with melt (IMO).

bbr2314

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Re: AMOC slowdown
« Reply #53 on: May 29, 2018, 10:49:59 PM »
See attached -- I would be extremely surprised if the residual albedo anomalies due to extra extant land-snowcover and the melt from that extra SWE/Greenland are unrelated to the worsening NATL anomalies we have seen this month. The currents may be the driver, but the situation ^^^ has, IMO, been a major aggravator to the current appearance.




sidd

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Re: AMOC slowdown
« Reply #54 on: May 30, 2018, 05:34:39 AM »
The graf in the post above is air temperature. SST is more appropriate in AMOC/Rahmstorf context.

sidd


Richard Rathbone

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Re: AMOC slowdown
« Reply #55 on: May 30, 2018, 02:33:46 PM »
In the response he indicated that melt has impact on surface salinity but not on largescale temperature.

"[Response: You mean by cold meltwater from Greenland flowing in? You can work that out from a simple heat budget calculation. The amount is far too small to matter for the large-scale sea surface temperature, but enough to matter for sea surface salinity. -Stefan] "

I did a simple heat calculation, and i agree with him.

sidd

Stefan's being a little disingenuous here. It makes a big difference to the cooling whether the ice melts on shore and meltwater enters the sea, or whether icebergs fall off Greenland and the ice melts at sea. Hansen reckoned that cooling was important enough to hose with a berg/meltwater mix rather than the traditional meltwater only, and I'm inclined to accept his judgement on it.


bbr2314

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Re: AMOC slowdown
« Reply #56 on: May 30, 2018, 04:50:58 PM »
In the response he indicated that melt has impact on surface salinity but not on largescale temperature.

"[Response: You mean by cold meltwater from Greenland flowing in? You can work that out from a simple heat budget calculation. The amount is far too small to matter for the large-scale sea surface temperature, but enough to matter for sea surface salinity. -Stefan] "

I did a simple heat calculation, and i agree with him.

sidd

Stefan's being a little disingenuous here. It makes a big difference to the cooling whether the ice melts on shore and meltwater enters the sea, or whether icebergs fall off Greenland and the ice melts at sea. Hansen reckoned that cooling was important enough to hose with a berg/meltwater mix rather than the traditional meltwater only, and I'm inclined to accept his judgement on it.

And I would argue it makes an even bigger difference if hosing effects in Quebec begin prior to other regions, amplifying albedo / extent beyond normal bounds, and allowing (relatively) cold continental winds to blow across the anomalous region, further compounding the cold blob...!

bbr2314

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Re: AMOC slowdown
« Reply #57 on: July 02, 2018, 07:39:38 PM »
Welp.

The change over the past 30 days has been extremely severe. I would say this is probably the worst disruption or occurrence of melt we have witnessed in the satellite era, at least in my recollection.

It looks like the second melt pulse of SWE in early June was the causative factor.



If this occurs with current departures vs. normal, I hate to think about what happens if we accumulate enough volume to result in a July melt pulse. It seems evident that the +++volume and April melt pulse was sufficient to stall May melt momentum substantially.

This begs the question of whether we need crazy departures for snow to make it through summer. If we have another 1000KM^3 of volume in 10-15 years, that could suffice for allowing enough melt pulsage that, by July/August, the remaining extant volume (now occupying a much greater area) is substantially more protected by the larger extant continental crysophere (further aided by decaying sea ice up north causing it to be "stuck" between oceanic ridging derived from continually accumulating heat). So summer quickly goes from abbreviated (2018) to non-existent (2035).

https://weather.gc.ca/saisons/animation_e.html?id=month&bc=sea


Alexander555

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Re: AMOC slowdown
« Reply #58 on: July 02, 2018, 09:41:09 PM »
A July melt puls ? If the information is correct there is less snow in the Americas below Canada. So how would that extra volume preventing the summer to kick in ? Would it not be possible that the area with snow cover gets smaller or the periodes shorter if the temperature keeps going up ? Anyway , you keep the debat going  ;)

bbr2314

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Re: AMOC slowdown
« Reply #59 on: July 03, 2018, 03:04:33 AM »
A July melt puls ? If the information is correct there is less snow in the Americas below Canada. So how would that extra volume preventing the summer to kick in ? Would it not be possible that the area with snow cover gets smaller or the periodes shorter if the temperature keeps going up ? Anyway , you keep the debat going  ;)
I am talking about future years. If we have another 1000KM^3 of volume vs 2018 by 2035, there will be enough mass that the spring melt pulses / ensuing protective freshwater runoff will allow the pack to last into July. You can see how the melting of the SWE follows distinctive pulses and doesn't run off all at once.

Also here is June 2018 vs. 2012. Some regions are now 20F+ colder (on monthlies!) than they were only six years ago.

AbruptSLR

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Re: AMOC slowdown
« Reply #60 on: July 30, 2018, 04:43:07 AM »
Consensus scientist's like to gamble with public safety that a slow-down of the AMOC it doesn't increase the rate of global warming, but that does not make it so:

Title: "Does a slow AMOC increase the rate of global warming?"

http://www.realclimate.org/index.php/archives/2018/07/does-a-slow-amoc-increase-the-rate-of-global-warming/
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FishOutofWater

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Re: AMOC slowdown
« Reply #61 on: July 30, 2018, 02:10:44 PM »
That cool area south of Greenland was not caused by melting of Canadian snow. The fresh water from Canadian snowmelt stays close to the coastline and moves south with the Labrador current.



The Greenland vortex pattern that has been dominating the weather since spring is the cause of that pattern. Storms and persistent NW winds down the Labrador sea has increased mixing in the Labrador and Greenland seas and cooled the surface layer.



The AMOC slowdown may be a problem for the Arctic sea ice because heat not transported northwards into the Labrador sea may be transported northeastwards wards into the Arctic ocean.

AbruptSLR

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Re: AMOC slowdown
« Reply #62 on: August 04, 2018, 08:12:55 PM »
The linked research provides more evidence that a slowing of the AMOC will lead to increased warming at high latitudes due to abrupt warming during the summer months (which increases Arctic Amplification):

G. Bromley et al. (06 April 2018), "Interstadial Rise and Younger Dryas Demise of Scotland's Last Ice Fields", Paleoceanography and Paleoclimatology, Vol. 33, Issue 4, https://doi.org/10.1002/2018PA003341

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2018PA003341

Abstract
Establishing the atmospheric expression of abrupt climate change during the last glacial termination is key to understanding driving mechanisms. In this paper, we present a new 14C chronology of glacier behavior during late‐glacial time from the Scottish Highlands, located close to the overturning region of the North Atlantic Ocean. Our results indicate that the last pulse of glaciation culminated between ~12.8 and ~12.6 ka, during the earliest part of the Younger Dryas stadial and as much as a millennium earlier than several recent estimates. Comparison of our results with existing minimum‐limiting 14C data also suggests that the subsequent deglaciation of Scotland was rapid and occurred during full stadial conditions in the North Atlantic. We attribute this pattern of ice recession to enhanced summertime melting, despite severely cool winters, and propose that relatively warm summers are a fundamental characteristic of North Atlantic stadials.

Plain Language Summary
Geologic data reveal that Earth is capable of abrupt, high‐magnitude changes in both temperature and precipitation that can occur well within a human lifespan. Exactly what causes these potentially catastrophic climate‐change events, however, and their likelihood in the near future, remains frustratingly unclear due to uncertainty about how they are manifested on land and in the oceans. Our study sheds new light on the terrestrial impact of so‐called “stadial” events in the North Atlantic region, a key area in abrupt climate change. We reconstructed the behavior of Scotland's last glaciers, which served as natural thermometers, to explore past changes in summertime temperature. Stadials have long been associated with extreme cooling of the North Atlantic and adjacent Europe and the most recent, the Younger Dryas stadial, is commonly invoked as an example of what might happen due to anthropogenic global warming. In contrast, our new glacial chronology suggests that the Younger Dryas was instead characterized by glacier retreat, which is indicative of climate warming. This finding is important because, rather than being defined by severe year‐round cooling, it indicates that abrupt climate change is instead characterized by extreme seasonality in the North Atlantic region, with cold winters yet anomalously warm summers.
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sidd

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Re: AMOC slowdown
« Reply #63 on: August 05, 2018, 07:59:56 AM »
How does that paper indicate that " a slowing of the AMOC will lead to increased warming at high latitudes due to abrupt warming during the summer months "

All i see is increased summer temperatures shortly after 12.8 to 12.6 Kyr BP.

sidd

bbr2314

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Re: AMOC slowdown
« Reply #64 on: August 05, 2018, 11:55:22 AM »
How does that paper indicate that " a slowing of the AMOC will lead to increased warming at high latitudes due to abrupt warming during the summer months "

All i see is increased summer temperatures shortly after 12.8 to 12.6 Kyr BP.

sidd
I would think it is because the "bubble" of super-warm ATL SSTs reaches the high Arctic, turns it ice-free, and forces progressively colder continents. This may be a self-reinforcing mechanism until the cold continents sufficiently overwhelm the SSTs to cause the Arctic to refreeze entirely. Thus, you end up with an "interlude" of extremely warm temps / summers in certain regions as the domino effect kicks in, which first occurs adjacent to extant ice sheets (i.e., Greenland), before spreading across the rest of the NHEM and resolving the warm oceanic anomalies.

AbruptSLR

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Re: AMOC slowdown
« Reply #65 on: August 06, 2018, 05:52:00 PM »
How does that paper indicate that " a slowing of the AMOC will lead to increased warming at high latitudes due to abrupt warming during the summer months "

All i see is increased summer temperatures shortly after 12.8 to 12.6 Kyr BP.

sidd

In addition to bbr2314's points, the fact that the Scottish glacier melted with a slowing AMOC is physical evidence of at least local Artic Amplification .
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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johnm33

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Re: AMOC slowdown
« Reply #66 on: August 07, 2018, 11:45:03 PM »
It looks like the AMOC is changing in a more complex way than just slowing. Open the ssh/t/s gifs on these two pages to look at the vortices and the various streams. https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/glfstr.html
https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/natspg.html
The way i see this is you have water coming out of the arctic moving more or less orthogonally away from the axis of rotation that has to gain 15mph/24kph every deg. it moves south to be at equilibrium. It's energetic state is indicated by the low ssh and the fact that it holds fast to the east coast as it moves south, both on Greenland and America. From the south there's water that has shifted about 110 and 1/8 closer [not much] in relation to the axis since it rose from the depths off equatorial Africa where it was already moving slower than the planets rotational speed which remains the case untill it gets to 35N . Then these two bodies meet and begin to exchange qualities, heat, inertia, salinity and spin one slows the other accelerates.
 There's a gif here that helps to visualise the tidal rotation around the amphidromic point in the N.ATL. also shown. Looking at the ssh gif in the second link above it appears that there are vortices of polar water moving south and east feeding a growing area of cooler water going south from Spain as far as the Cape Verde islands. The amphidromic point seems to coincide with a relatively quiet [vortice wise] area of the N.ATL. on Nullschool . It appears that this fraction of water is being drawn south away from there as the tides rotate, whether this is permanent or just one of the random fluctuations we can expect ?
hope that makes sense.
 

AbruptSLR

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Re: AMOC slowdown
« Reply #67 on: August 14, 2018, 11:06:54 PM »
The linked reference evaluates various factors influencing the AMO including the AMOC.  It does note that a slowdown of the AMOC results in a warming of the Tropical Atlantic waters:

ROBERT C. J. WILLS et a;. (2018), "Ocean-atmosphere dynamical coupling fundamental to the Atlantic Multidecadal Oscillation", Journal of Climate,

https://atmos.washington.edu/~rcwills/papers/2018_Wills_etal_AMO_JClim.pdf

Abstract: "The North Atlantic has shown large multidecadal temperature shifts during the 20th century. There is ongoing debate about whether this variability arises primarily through the influence of atmospheric internal variability, through changes in ocean circulation, or as a response to anthropogenic forcing. This study isolates the mechanisms driving Atlantic temperature variability on multidecadal timescales by using low-frequency component analysis (LFCA) to separate the influences of high-frequency variability, multidecadal variability, and long-term global warming. This analysis objectively identifies the North Atlantic subpolar gyre as the dominant region of Atlantic multidecadal variability. In unforced control runs of coupled climate models, warm subpolar temperatures are associated with a strengthened Atlantic Meridional Overturning Circulation (AMOC) and anomalous local heat fluxes from the ocean into the atmosphere. Atmospheric variability plays a role in the intensification and subsequent weakening of ocean overturning and helps to communicate warming into the tropical Atlantic. These findings suggest that dynamical coupling between atmospheric and oceanic circulations is fundamental to the Atlantic Multidecadal Oscillation (AMO) and motivate approaching decadal prediction with a focus on ocean circulations."
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Niall Dollard

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Re: AMOC slowdown
« Reply #68 on: August 22, 2018, 10:52:46 AM »
2018 International AMOC Science Meeting Agenda

There is a wealth of information available here on the current state of the AMOC, with many of the presentations freely available to download :

https://usclivar.org/meetings/2018-amoc-rapid-meeting-agenda

bluesky

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Re: AMOC slowdown
« Reply #69 on: September 18, 2018, 05:37:27 PM »
A new paper makes the dot between drop in oxygen content in St Laurent estuary, weakening of the Labrador current and a correlation with weakening AMOC

"Rapid coastal deoxygenation due to ocean circulation shift in the northwest Atlantic"
Mariona Claret et al. Sept 2018

Abstract
"Global observations show that the ocean lost approximately 2% of its oxygen inventory over the past five decades1,2,3, with important implications for marine ecosystems4,5. The rate of change varies regionally, with northwest Atlantic coastal waters showing a long-term drop6,7 that vastly outpaces the global and North Atlantic basin mean deoxygenation rates5,8. However, past work has been unable to differentiate the role of large-scale climate forcing from that of local processes. Here, we use hydrographic evidence to show that a Labrador Current retreat is playing a key role in the deoxygenation on the northwest Atlantic shelf. A high-resolution global coupled climate–biogeochemistry model9 reproduces the observed decline of saturation oxygen concentrations in the region, driven by a retreat of the equatorward-flowing Labrador Current and an associated shift towards more oxygen-poor subtropical waters on the shelf. The dynamical changes underlying the shift in shelf water properties are correlated with a slowdown in the simulated Atlantic Meridional Overturning Circulation (AMOC)10. Our results provide strong evidence that a major, centennial-scale change of the Labrador Current is underway, and highlight the potential for ocean dynamics to impact coastal deoxygenation over the coming century."

under paywall, but I think it can be requested on research gate so should be accessible:
https://www.researchgate.net/publication/327702404_Rapid_coastal_deoxygenation_due_to_ocean_circulation_shift_in_the_northwest_Atlantic

sidd

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Re: AMOC slowdown
« Reply #70 on: September 25, 2018, 10:18:01 PM »
Here is an interesting paper in GRL on a global climate model that has a bistablity between glaciated and nonglaciated states. It is a crude model, but rather nice in that it explicitly shows the origin of the bistability.

"Two stable equilibria of climate are supported, one "Cold" and one "Warm" for the same external forcing and parameters, thus demonstrating that multiple equilibria are possible in a coupled GCM comprising a myriad of degrees of freedom. The difference in the climate of the two states is of planetary scale. Global average sea surface temperature and surface air temperature differ by 8.2 and 13.5 ∘ C, respectively (patterns are shown in Figure S1). In the southern hemisphere (SH), the sea ice edge (as measured by the 15% annual mean concentration) expands by about 15 ∘ of latitude in the Cold state (Figure 1). The northern hemisphere, which is nearly ice free in the Warm state, exhibits a large ice cap extending over the subpolar gyre (45 N) in the Cold state, with a similar expansion of snow cover over land (Figure 1, top left)."

Why do i post the paper in this thread: Because the bistability is not driven by AMOC collapse:

"The multiple states described here differ fundamentally from AMOC bistability and are supported by coupled ocean-atmosphere-sea ice dynamics. Although the MOC does change between states in our simulations (Figure 3), this change does not correspond to a collapse and is in fact a symptom rather than a driver of the bistability (Ferreira et al., 2011)."


I attach fig 1

sidd

bbr2314

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Re: AMOC slowdown
« Reply #71 on: November 14, 2018, 08:18:53 AM »
I don't know where to ask this question so perhaps this is the right place. While shelf temps along the NE seaboard are dropping, the EURO is showing what I believe to be an unprecedented surge of heat developing and arriving very close offshore (GIF is 11/23/2017 vs 2018). This starts around D4 and the end result appears to follow the continental shelf fairly closely. So what is causing this / could it be the freshwater input from whatever happened with Beaufort Gyre this summer (maybe it intensified the GS response?) or also albedo / SST interaction due to Quebec's snowy autumn?

This may portend significant disturbances down the line as well.


oren

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Re: AMOC slowdown
« Reply #72 on: November 14, 2018, 09:53:44 AM »
Interesting but I think the best time to ask that question is after this event will have happened, in 10 days from now. Then the comparison will be fully valid.

bbr2314

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Re: AMOC slowdown
« Reply #73 on: November 15, 2018, 06:20:43 AM »
Interesting but I think the best time to ask that question is after this event will have happened, in 10 days from now. Then the comparison will be fully valid.
So after your rebuke I went back and compared EURO forecasts for the same region in recent weeks with reality upon verification. And you are correct to be wary, because it appears the EURO has a systemic bias of GREATLY overwarming the NATL adjacent to the NE seaboard. This is actually very good to know and it partially explains why it is always too progressive with ejecting airmasses from Northeast North America (fake oceanic warmth -> more ridging, verification of less warmth -> more troughing vs forecast).

aperson

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Re: AMOC slowdown
« Reply #74 on: November 15, 2018, 06:30:15 AM »
The ECMWF wasn't even atmosphere-ocean coupled until this year. It's definitely got a long way to go before it can be used as any sort of useful indicator for D10 SSTs. A lot of the other global models aren't even coupled altogether.

Sleepy

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Re: AMOC slowdown
« Reply #75 on: November 15, 2018, 06:48:53 AM »
https://www.ecmwf.int/en/newsletter/156/meteorology/ifs-upgrade-brings-more-seamless-coupled-forecasts
Quote
On 5 June 2018, ECMWF implemented a substantial upgrade of its Integrated Forecasting System (IFS). IFS Cycle 45r1 brings coupling to all ECMWF forecasts, from forecast day 1 to one year, by including the three-dimensional ocean and sea-ice model in the single high-resolution forecast (HRES). This is a further step towards the implementation of the 2016–2025 Strategy, whose goals include a more complete and seamless description of the Earth system across all ECMWF configurations.
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Pmt111500

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Re: AMOC slowdown
« Reply #76 on: November 15, 2018, 08:29:15 AM »
https://www.ecmwf.int/en/newsletter/156/meteorology/ifs-upgrade-brings-more-seamless-coupled-forecasts
Quote
On 5 June 2018, ECMWF implemented a substantial upgrade of its Integrated Forecasting System (IFS). IFS Cycle 45r1 brings coupling to all ECMWF forecasts, from forecast day 1 to one year, by including the three-dimensional ocean and sea-ice model in the single high-resolution forecast (HRES). This is a further step towards the implementation of the 2016–2025 Strategy, whose goals include a more complete and seamless description of the Earth system across all ECMWF configurations.
Browser crashed, not going to write the longer response again. Looks like the tropical forecasts get an improvement in ecmwf. Does someone know if they incorporate weekends, holidays and similar cultural effects on their model? Simple yes or no will do. I mean, have they checked if forecasts made on Monday data are more accurate than those done on Fridays' data? This might be one way to improve on longer forecasts, but would require some predictability of human behavior... Not something many endorse, it's entirely possible humans stop emissions on their freetime instead of rushing to the shores of plastic seas.
« Last Edit: November 15, 2018, 12:14:38 PM by Pmt111500 »
Amateur observations of Sea Ice since 2003.

Sleepy

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Re: AMOC slowdown
« Reply #77 on: November 15, 2018, 09:38:32 PM »
Pmt, I haven't thought about that but it seems like they will hit the roof soon (with todays tech) even without incorporating human behaviour.
https://www.ecmwf.int/en/about/what-we-do/scalability
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gerontocrat

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Re: AMOC slowdown
« Reply #78 on: November 15, 2018, 10:06:10 PM »
Pmt, I haven't thought about that but it seems like they will hit the roof soon (with todays tech) even without incorporating human behaviour.
/quote]
I wonder if a similar sort of scary graph is where mankind is going on power use by computer /communications gear in general as world-wide systems and data storage expand exponentially . Chuck in AI, which apparently requires a quantum jump in data and processing power, and ......

ps: My doubts on AI have always been that the brain must work fundamentally differently from computers. The brain has ridiculously low processing speeds and pathetically low amounts of data storage but.....

pps: But should I be reminding sleepy of his less than wonderful experiences of the IT industry.
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Sleepy

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Re: AMOC slowdown
« Reply #79 on: November 15, 2018, 10:28:17 PM »
Oh, they were wonderful gerontocrat, I had everything except a life. Now it's the other way around. And you?
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gerontocrat

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Re: AMOC slowdown
« Reply #80 on: November 15, 2018, 11:45:39 PM »
Oh, they were wonderful gerontocrat, I had everything except a life. Now it's the other way around. And you?
It was good for a long time in some of the poorest parts of the world. I even did stuff for the Swedish International Development Association - they sent me to Vasteras to learn Portuguese..

But socialism died, the demand was to support privatisation and the Anglo-Saxon Capitalist model. Once I was sent a project proposal to tax famine ( I kid you not). So in the end I chucked it. I have a CV that says to prospective employers - you did too much, you know too much. Over-qualified people are unemployable.

So nowt to do now but be a witness to the coming shit-storm and try to persuade my daughter to prepare her defences. People tell me to write the book - it seems we all have one book inside us. Too much like hard work?

AMOC slowdown ? whoops.
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Pmt111500

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Re: AMOC slowdown
« Reply #81 on: November 16, 2018, 05:26:11 AM »
Oh, they were wonderful gerontocrat, I had everything except a life. Now it's the other way around. And you?
I have a CV that says to prospective employers - you did too much, you know too much. Over-qualified people are unemployable.
AMOC slowdown ? whoops.
AMOC slowdown.
It could be the increased heat absorption by the AGW in the North Atlantic is responsible for the continued decrease of ice in the Arctic Atlantic sector. Rather than trying to directly measure the heat transport from Tropics we might do better relying on satellite/ship measurements over the whole North Atlantic. It's been clear that East Greenland and Baffin current systems have brought an almost steady feed of cold water southwards.
Nowadays, probably for 3 years now the Nares transport has been diminishing (well way longer, just throwing a number here) and the eastern parts of north Atlantic currents have on occasion backtracked (not sure this is how it happens) along the edge of the ice all the way over the northern tip of Greenland. Thus the heat transport via the North Atlantic eastern coasts might be seen to be a factor in the melt of NE Greenland, a place at least I once thought to be among the last to start melting.
This heat absorbed by the Eastern North Atlantic might neatly connect to the bbr hypothesis of Quebec and Labrador harshness. Cutting out a conduit (the East Greenland Current and Nares Transport) for cold waters might increase transport elsewhere (CAA channels), unless the ice melts in place.
Anyway, the 'cold patch' South of Greenland, occasionally can manifest itself on a much wider area in CAA, Labrador and Quebec giving the residents (and bbr) much to talk about. Personally I do not think part of Greenland ice should melt and be transported by warped airflows to the mainland Canada. What the cold patch (along with its other counterpart (the other one in the Southern hemisphere might be a figment of  my imagination) warmch in North Pacific) does do is to help create the Ridiculously Resilient Ridge and the associated high amplitude waves over the whole hemisphere. Thus we might see bbrs' hypothesis as an extreme case of standing waves directing only cold rains (yea, it's snow) towards Canadian eastern seaboard.

That is about my current understanding of what's happening in Overturning, I know salinity plays a role in the Ocean, but I left it out since I don't get it well enouhj.
« Last Edit: November 16, 2018, 06:08:09 AM by Pmt111500 »
Amateur observations of Sea Ice since 2003.

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Re: AMOC slowdown
« Reply #82 on: November 16, 2018, 05:52:34 AM »
Another by Wei Liu, paywalled and not (yet) available to cheap non paying customers.

The mechanisms of the Atlantic Meridional Overturning Circulation slowdown induced by Arctic sea ice decline
https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0231.1
Quote
We explore the mechanisms by which Arctic sea ice decline affects the Atlantic Meridional Overturning Circulation (AMOC) in a suite of numerical experiments perturbing Arctic sea ice radiative budget within a fully coupled climate model. The imposed perturbations act to increase the amount of heat available to melt ice, leading to a rapid Arctic sea ice retreat within 5 years after the perturbations are activated. In response, the AMOC gradually weakens over the next ∼100 years. The AMOC changes can be explained by the accumulation in the Arctic and subsequent downstream propagation to the North Atlantic of buoyancy anomalies controlled by temperature and salinity. Initially, during the first decade or so, the Arctic sea ice loss results in anomalous positive heat and salinity fluxes in the subpolar North Atlantic, inducing positive temperature and salinity anomalies over the regions of oceanic deep convection. At first, these anomalies largely compensate one another, leading to a minimal change in upper ocean density and deep convection in the North Atlantic. Over the following years, however, more anomalous warm water accumulates in the Arctic and spreads to the North Atlantic. At the same time, freshwater that accumulates from seasonal sea ice melting over most of the upper Arctic Ocean also spreads southward, reaching as far as south of Iceland. These warm and fresh anomalies reduce upper ocean density and suppress oceanic deep convection. The thermal and haline contributions to these bouyancy anomalies, and therefore to the AMOC slowdown during this period, are found to have similar magnitudes. We also find that the related changes in horizontal wind-driven circulation could potentially push freshwater away from the deep convection areas and hence strengthen the AMOC, but this effect is overwhelmed by mean advection.

Edit; that didn't take long...
« Last Edit: November 16, 2018, 07:56:10 AM by Sleepy »
Omnia mirari, etiam tritissima.
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Science is a jealous mistress and takes little account of a man's feelings.