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IanR

The weakening of the North Atlantic circulation

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With the recent cold anomalies in the north atlantic affecting the early summer temperatures, such as may and june below average and very possible july, despite the hot start.   Is this a result of the north atlantic circulation aka 'gulf stream' slowing?  

If so, whats the causes? freshwater melt from the artic seems to be the biggest culprit, if this is the case, it will be a long term and possibly irreversable trend, Should we not be underestimate the huge change on the uk climate which will occur which could be starting now?, It will be interesting to hear peoples opinion on this, especially the more knowledgeable of the oceanic dynamics ?

 

Interesting times ahead to see where this goes   

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I'm not sure it's correct to attribute a couple of cool months to the Atlantic SST anomaly which has been around a while. There is much going on in NH of late so I think serious comments on our cool period will require hindsight and is way above my pay grade. Anyway for starters:

 

What’s going on in the North Atlantic?
 

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Fresh melt water from Greenland and a stuck jet keeping eastern US frigid over winter (cold air which then flows out over the ocean keeping it chilled) plus increases in blocking?

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The cold pool has been around for a couple of years but the reasons could be various....

 

.... unprecedented ice melt in recent decade

 

.... remarkably cold air masses in the central Atlantic over the last two winters

 

.... a known tendency for a cold Atlantic during very low solar periods - the AMOC fell like a stone during 09/10 - is this cause or effect?

 

.... is this just the beginning of the natural cycle to negative AMO?

 

With regards to impact on current weather, the recent weather patterns have allowed for full effects to be felt and it is a good bit cooler than this time last year.

 

this year   CxamiFi.png   last year   76VFTTl.png

 

 

I actually feel that this thread should be in the weather section - a much wider audience - as long as the sniping can be left aside.

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Fresh melt water from Greenland and a stuck jet keeping eastern US frigid over winter (cold air which then flows out over the ocean keeping it chilled) plus increases in blocking?

 

I don't think there has been that much high latitude blocking until fairly recently GW.

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There is an old thread on SSTs in the weather section.... here we go https://forum.netweather.tv/topic/62702-sea-surface-temperatures/page-17.

 

Lets remember, recent data from the RAPID array have found a trend for a slowdown in the circulation,  so it does appear to be a slightly longer term issue. 

 

http://www.sciencemag.org/content/348/6241/1255575

 

F1.medium.gif

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One thing to keep in mind when considering the coolllsh couple of months in the UK, particularly the northern half, the air has often been sourced around the Great Lakes/Canada.

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With the cool SSTs featuring in the media yesterday, I thought I would check if much change one month on.

 

DvZ5ftK.png

 

This discussion rang some bells regarding a model simulation paper I had read years ago - thanks to GS, I found the article and include here for any other view points.

 

http://www.nature.com/nature/journal/v409/n6817/full/409171a0.html

 

I'm not saying something of this severity is taking place but there have been many lesser instances documented in the Greenland ice-core and sea bed fossil record. Certainly been a tendency for anomalous NW winds in the region - has the Greenland current responded and is that helping export ice. A chicken or egg feedback loop?

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With the cool SSTs featuring in the media yesterday, I thought I would check if much change one month on.

 

DvZ5ftK.png

 

This discussion rang some bells regarding a model simulation paper I had read years ago - thanks to GS, I found the article and include here for any other view points.

 

http://www.nature.com/nature/journal/v409/n6817/full/409171a0.html

 

I'm not saying something of this severity is taking place but there have been many lesser instances documented in the Greenland ice-core and sea bed fossil record. Certainly been a tendency for anomalous NW winds in the region - has the Greenland current responded and is that helping export ice. A chicken or egg feedback loop?

 

Interesting study.

 

Here's an animation of the N. Atlantic SSTs so far this year (last frame is just the last week).

 

HNIGl4C.gif

 

The SLP anomaly appears to be very similar to what the study you linked to shows (note the colour scale in the study figure are the opposite of the reanalysis map).

 

uowTB0d.gif 409171ac.2.jpg

 

 

However, we haven't see all that much extra export through the Fram strait this year, although It has picked up during the last month.

 

Below is the wind vector anomalies for the year to July 1st, and since July 1st.

 

hA3UL5E.gif fZiV9zh.gif

 

Those north westerlies have been very strong over the last 6 weeks, but nothing unusual at all in the 7 months before. The sea ice area along the east of Greenland shows nothing unusual this year either. Given that the ice is so thin now anyway, extra export wouldn't contribute a whole lot of extra fresh water anyway. We'd be more reliant on stripping away fresh water from the top of the Arctic halocline

 

region.all.anom.region.5.jpg recent365.anom.region.5.jpg

 

I guess it's a case of wait and see for now.

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I think your point regarding the wind vector anomalies for this year quite pertinent. I'm having a mental block at the moment but how unusual is this years cold anomaly in the context of historical variability of the Atlantic SST anomaly? I'm under the impression it's within the usual parameters but I'm not sure why I think that.

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I think your point regarding the wind vector anomalies for this year quite pertinent. I'm having a mental block at the moment but how unusual is this years cold anomaly in the context of historical variability of the Atlantic SST anomaly? I'm under the impression it's within the usual parameters but I'm not sure why I think that.

 

If we take the SST anomaly from say 45-60N, and 15-45W (looks roughly to cover the main area of cold) for the last 5 months, we see it's actually the coldest on record, albeit by a small margin.

 

RvbmXvu.png

 

 

Coldest on record by even more when just looking at July.

 

iUG3fwg.png

 

It is unusual, but whether it's really tied to a slow down in the AMOC or whether it normal variability is hard to say.

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Thanks for that. That's what was bugging me as I had actually seen those graphs and indeed I think I actually posted one of them!! It's an age thing. As you say tricky whether it's normal variability or not and it will be interesting to see whether the reversal of the anomaly comes to pass by next spring as forecast. Keeping in mind lrfs of SSTs come with usual health warning.

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Thanks for that. That's what was bugging me as I had actually seen those graphs and indeed I think I actually posted one of them!! It's an age thing. As you say tricky whether it's normal variability or not and it will be interesting to see whether the reversal of the anomaly comes to pass by next spring as forecast. Keeping in mind lrfs of SSTs come with usual health warning.

 

Now worries. I doubt the seasonal models could pick up on a slowdown in the AMOC, so I'd be fairly sceptical of what they'd show (provided these anomalies are driven by the AMOC). 

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If this lasts into the autumn and winter then I guess we could see some more intense Atlantic lows than usual due to the steep thermal contrast?

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If this lasts into the autumn and winter then I guess we could see some more intense Atlantic lows than usual due to the steep thermal contrast?

 

Or would the cold N. Atlantic mean less of a temperature difference to the Arctic? I also think because the likelihood of a very low sea ice minimum this year, the Autumn could be quite mild over the Arctic (as the heat absorbed by the ocean is released during the polar night). So the combination of a milder than average Arctic and colder than average N. Atlantic could mean a much reduced temperature gradient this Autumn and a more wavy jet stream. Then it comes down to whether we get caught in a jet stream trough or ridge...

 

It will be fascinating to follow anyway!

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Or would the increased sea-track cause greater early-season snowfalls, in locations adjacent to the Baltic Sea and the Arctic Ocean? Who knows? :D

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BFTV, thanks for enlightening posts with recent reanalysis data.

 

Knocker, the new Francis paper is a very good read - first time seeing it, the research serves to prove how susceptible the N. Atlantic region is to change.

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A tweet by Eric Blake. Nouska has already posted the SST diagram in an earlier discussion.

 

Eric Blake â€@EricBlake12 2h2 hours ago

CFS SSTs fcst to Spring '16- Atlc SSTs warm thru atmospheric bridge while #ElNino decays HT

 

Now I wasn't sure what he meant by atmospheric bridge so went looking, as one does, and found this in a paper:

 

The Atmospheric Bridge: The Influence of ENSO Teleconnections on Air–Sea Interaction over the Global Oceans

 

 

While air–sea interactions responsible for El Nin˜o and the Southern Oscillation (ENSO) are centered in the equatorial Pacific Ocean, changes in tropical convection associated with ENSO influence the global atmospheric circulation. The ENSO-driven large-scale atmospheric teleconnections alter the near-surface air temperature, humidity, and wind, as well as the distribution of clouds far from the equatorial Pacific. The resulting variations in the surface heat, momentum, and freshwater fluxes can induce changes in sea surface temperature (SST), salinity, mixed layer depth (MLD), and ocean currents. Thus, the atmosphere acts as a bridge spanning from the equatorial Pacific to the North Pacific, illustrated in Fig. 1, and to the South Pacific, the Atlantic, and Indian Oceans. The ENSO-related SST anomalies that develop over the world’s oceans can also feed back on the original atmospheric response to ENSO.

 

https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&ved=0CEYQFjAEahUKEwjsq8iHm6THAhXJVxoKHUcNBlg&url=http%3A%2F%2F140.172.38.100%2Fpsd%2Fpeople%2Fmichael.alexander%2Falexander.etal.atm-bridge.jcli-02.pdf&ei=b5XLVay4FMmvaceamMAF&usg=AFQjCNHK7PbJRNLnMMOx3HE6FXtgyGYv2A&sig2=uaw1DmL9nvPIs6gl7s5QWQ&bvm=bv.99804247,d.d2s&cad=rja

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I've just checked out the past 22 years' worth of N. Atlantic SST anomalies and 300hPa zonal wind anomalies for the period Nov-Mar (using NCEP/NCAR Reanalysis charts).

 

Overlaying where the peak zonal winds occur onto respective SST charts, 12 of those years display some hints of a correlation between the two, with the peak zonal winds (hence the jet stream, for the most part) tending to favour a track that takes it over or just south of negative SST anomalies, or over the northernmost extent of positive SST anomalies. Here's a snapshot of the lot - I'll admit that 2008 is stretching it a bit as the jet was a bit further south than my proposed relationship with SST anomalies suggests.

 

Nov-Mar%20SST-Zonals%20Suggesting%20Corr

 

 

...but then there's the remaining 10 years which tend to defy the theory in its entirety. I'm still looking at those, as closer inspection may reveal some reasons why (though I'm not expecting much. Also, it appears I may have 1999 in the wrong group (should have been included above). This is all work in progress - if you have any ideas or thoughts then I'm all ears!   :gathering:  ...or should that be eyes?  :crazy:

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any latest on this area gents? I have seen a few forums where there has been mention of the northern part of the Gulf Stream heading a little further south... but nothing to back it up or to confirm if its normal for this time of year? I think the MET also suggested that whilst 2015 and 2016 would be globally warmer that western EU could be cooler.. cant remember if that was due to the link of the GS or not?

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any latest on this area gents? I have seen a few forums where there has been mention of the northern part of the Gulf Stream heading a little further south... but nothing to back it up or to confirm if its normal for this time of year? I think the MET also suggested that whilst 2015 and 2016 would be globally warmer that western EU could be cooler.. cant remember if that was due to the link of the GS or not?

 

Its in the Daily Mail today so must be true

 

"""The Gulf Stream system slowing down more than it has for 1,000 years"

 

http://www.dailymail.co.uk/sciencetech/article-3254786/Should-fear-North-Atlantic-blob-Climate-scientists-warn-record-cold-ocean-sign-changes-ocean

 

Watch out for the Daily Express article shortly and -20c in London next January

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The cold pool has been around for a couple of years but the reasons could be various....

 

.... unprecedented ice melt in recent decade

 

.... remarkably cold air masses in the central Atlantic over the last two winters

 

.... a known tendency for a cold Atlantic during very low solar periods - the AMOC fell like a stone during 09/10 - is this cause or effect?

 

.... is this just the beginning of the natural cycle to negative AMO?

 

With regards to impact on current weather, the recent weather patterns have allowed for full effects to be felt and it is a good bit cooler than this time last year.

 

this year      last year  

 

 

I actually feel that this thread should be in the weather section - a much wider audience - as long as the sniping can be left aside.

 

Please excuse the quoting of my own post but this article talks about point two above. Putting in here as a very climate based paper and don't want the other thread going off on a tangent.

 

https://www2.ametsoc.org/ams/index.cfm/publications/bulletin-of-the-american-meteorological-society-bams/state-of-the-climate/chapter-3-global-oceans/

 

Page 66 ....

 

 

XWCnEar.png  

 

 

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Please excuse the quoting of my own post but this article talks about point two above. Putting in here as a very climate based paper and don't want the other thread going off on a tangent.

 

https://www2.ametsoc.org/ams/index.cfm/publications/bulletin-of-the-american-meteorological-society-bams/state-of-the-climate/chapter-3-global-oceans/

 

Page 66 ....

 

 

XWCnEar.png

An excellent link which doesn't go off at a tangent and is highly pertinent to the other thread. It suggests that "Atlantic basin-scale SST variability in 2014 was driven primarily by atmospheric forcing. In particular, pronounced atmospheric cooling over much of the subpolar gyre", as I for one suspected.

Indeed, far from reduced MOC, the cooling has led to increased deep water formation.

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