Cooler Atlantic

[ItNeverSnowsInWindsor]

If September and October deliver below average temperatures to the UK could the waters around the UK become close to average rather than the strongly above average temperatures progged by the Meto long range probability maps over the next few months ?

How quickly can the SSTs change ?

[Recretos]

SSTs can change fairly quickly with upwelling, and also in the opposite direction. Another thing is a prolonged cyclonic activity which mixes a good depth of the ocean (relatively).

Just for this thread I have made two charts, showing that the "cold" blob from 2015 is pretty much gone compared to this year. First is a direct monthly mean comparison, and second is a difference at 75m depth, where the N Atlantic is warmer than it was in 2015 in the first week of September. 

   

 

[Blessed Weather]

I'm puzzled - did we miss the following report? I've glanced back through the thread and can't find it referenced in any posts but it's very interesting reading that suggests a link between the 2015 cold blob and the heatwave across Europe that year. Furthermore, a cold Atlantic anomaly seems to have preceded other European heatwaves dating back to 1980.

Abstract:
Drivers of exceptionally cold North Atlantic Ocean temperatures and their link to the 2015 European heat wave
The North Atlantic and Europe experienced two extreme climate events in 2015: exceptionally cold ocean surface temperatures and a summer heat wave ranked in the top ten over the past 65 years. Here, we show that the cold ocean temperatures were the most extreme in the modern record over much of the mid-high latitude North-East Atlantic. Further, by considering surface heat loss, ocean heat content and wind driven upwelling we explain for the first time the genesis of this cold ocean anomaly. We find that it is primarily due to extreme ocean heat loss driven by atmospheric circulation changes in the preceding two winters combined with the re-emergence of cold ocean water masses. Furthermore, we reveal that a similar cold Atlantic anomaly was also present prior to the most extreme European heat waves since the 1980s indicating that it is a common factor in the development of these events. For the specific case of 2015, we show that the ocean anomaly is linked to a stationary position of the Jet Stream that favours the development of high surface temperatures over Central Europe during the heat wave. Our study calls for an urgent assessment of the impact of ocean drivers on major European summer temperature extremes in order to provide better advance warning measures of these high societal impact events.

Full paper: http://iopscience.iop.org/article/10.1088/1748-9326/11/7/074004/meta;jsessionid=36846BA815A6E3397F71CC09EEA3D084.ip-10-40-2-120

[Singularity]

How far we've come... the current predominance in the N. Atlantic of +0.5*C and greater anomalies is extraordinary, or at least it seems that way to me as I can't recall seeing so few blue colours present in the region before. 

The cold pool has certainly met its demise. If it wasn't for so much warmth to the south of that area, we'd have reason to expect significantly reduced N. Atlantic cyclogenesis this Jan-Mar compared to climatology. As it is, it should be less than we saw during 2014-16.

[ArHu3]

3 hours ago, Singularity said:

How far we've come... the current predominance in the N. Atlantic of +0.5*C and greater anomalies is extraordinary, or at least it seems that way to me as I can't recall seeing so few blue colours present in the region before. 

The cold pool has certainly met its demise. If it wasn't for so much warmth to the south of that area, we'd have reason to expect significantly reduced N. Atlantic cyclogenesis this Jan-Mar compared to climatology. As it is, it should be less than we saw during 2014-16.

 

Looks much colder on NOAA map

 

What looks remarkable to me are the blue patches in the Gulfstream 

Edited January 6, 2018 by ArHu3

[Midlands Ice Age]

1 hour ago, ArHu3 said:

 

Looks much colder on NOAA map

 

What looks remarkable to me are the blue patches in the Gulfstream 

Yep Guys..

 I always find it incredible the difference it makes in having neutral +0.5C to -0.5C in the above chart comparisons.

I would guess that at least 50% of the earth's ocean temperatures (SST's)  reside at either just below or just above 0.

MIA 

[Singularity]

Yes I prefer the -0.5 to +0.5 having no shading as such small departures are of little significance.

 

As for the blue patches in the Gulf Stream, it has always looked like that since the resolution of analysis improved, as the oceanic current features hundreds of small eddies that bring colder air down on one side and warmer air up on the other, resulting in the mixed anomaly picture.

[ArHu3]

1 hour ago, Singularity said:

Yes I prefer the -0.5 to +0.5 having no shading as such small departures are of little significance.

 

As for the blue patches in the Gulf Stream, it has always looked like that since the resolution of analysis improved, as the oceanic current features hundreds of small eddies that bring colder air down on one side and warmer air up on the other, resulting in the mixed anomaly picture.

There are still big differences, look at Hudson Bay, it's dark red in your pic indicating around +4 anomaly whereas the other is mostly yellow with some light orange but also blues or the yellow sea west of the Korean peninsula, red in one blue in the other pic

Edited January 7, 2018 by ArHu3

[Midlands Ice Age]

52 minutes ago, ArHu3 said:

There are still big differences, look at Hudson Bay, it's dark red in your pic indicating around +4 anomaly whereas the other is mostly yellow with some light orange but also blues or the yellow sea west of the Korean peninsula, red in one blue in the other pic

AerHu3...

 I think you are talking about Baffin Bay and not Hudson Bay.

Hudson is now totally covered in ice (much earlier than usual) and does not feature on either map.

The area in question is I think classed as Baffin Bay

To give a clue I went to Maisie to see what happened to the forming ice in Baffin and yesterday it fell by 28K so I am guessing that it is experiencing some WAA. This has happened several times this year.

Go to

http://nsidc.org/data/masie    

and download the CSF file into Excel to view the ice areas.

My worry is that I do not believe that the daily temp change will affect the SST's at that speed.

It  is worth keeping an 'eye' on it for a week to check against any ice melt or growth.

MIA

[knocker]

 

[Fozfoster]

On 10/01/2018 at 06:27, knocker said:

 

Hi knocker. I thought  the Gulf Stream was getting weaker! 

[knocker]

 

[Singularity]

In the AMO series I have noticed a tendency for Feb-Apr to be cooler than the other months during warm phases, which may well be a reflection of the many historical incidences of a +NAO January along with some cases of anomalously cold air spilling out from eastern N. America.

The latter will be most pronounced and it appears we'll be having one of those next week. Could put quite a dent in the run of very positive AMO months we've recently had.

[Blessed Weather]

Interesting tweet and associated report from the RAPID team monitoring the Atlantic Overturning Circulation. Report abstract and tweet:

The North Atlantic Ocean is in a state of reduced overturning
Abstract

The Atlantic Meridional Overturning Circulation (AMOC) is responsible for a variable and climatically important northward transport of heat. Using data from an array of instruments that span the Atlantic at 26°N, we show that the AMOC has been in a state of reduced overturning since 2008 as compared to 2004-2008. This change of AMOC state is concurrent with other changes in the North Atlantic such as a northward shift and broadening of the Gulf Stream, and altered patterns of heat content and sea-surface temperature. These changes resemble the response to a declining AMOC predicted by coupled climate models.

http://onlinelibrary.wiley.com/doi/10.1002/2017GL076350/full

 

[Fozfoster]

On 29/01/2018 at 22:50, Fozfoster said:

Hi knocker. I thought  the Gulf Stream was getting weaker! 

Or is cooler or both?

[Weather-history]

This winter has been a polar maritime dominate one especially the second half, the very cold pools of airmasses  constantly been pulled off the Labrador region into the North Atlantic must be having an impact on SSTs in the north Atlantic. 

Edited February 10, 2018 by Weather-history

[Matthew.]

37 minutes ago, Weather-history said:

This winter has been a polar maritime dominate one especially the second half, the very cold pools of airmasses  constantly been pulled off the Labrador region into the North Atlantic must be having an impact on SSTs in the north Atlantic. 

The easterly QBO 2014/15 winter had the same airmass dominating. The difference being this time the Atlantic is weaker and more meridional. Certainly a pattern there. Whereas 2013/14 and 15/16, 16/17 westerly QBO winters had a more tropical signature

[Blessed Weather]

Very interesting sounding report published last week on Nature.com suggesting an accumulating effect from freshwater build-up following summer ice melt. It's behind a paywall - does anyone know how/where to access a copy for free?

Increased risk of a shutdown of ocean convection posed by warm North Atlantic summers

Abstract:

A shutdown of ocean convection in the subpolar North Atlantic, triggered by enhanced melting over Greenland, is regarded as a potential transition point into a fundamentally different climate regime. Noting that a key uncertainty for future convection resides in the relative importance of melting in summer and atmospheric forcing in winter, we investigate the extent to which summer conditions constrain convection with a comprehensive dataset, including hydrographic records that are over a decade in length from the convection regions. We find that warm and fresh summers, characterized by increased sea surface temperatures, freshwater concentrations and melting, are accompanied by reduced heat and buoyancy losses in winter, which entail a longer persistence of the freshwater near the surface and contribute to delaying convection. By shortening the time span for the convective freshwater export, the identified seasonal dynamics introduce a potentially critical threshold that is crossed when substantial amounts of freshwater from one summer are carried over into the next and accumulate. Warm and fresh summers in the Irminger Sea are followed by particularly short convection periods. We estimate that in the winter 2010–2011, after the warmest and freshest Irminger Sea summer on our record, ~40% of the surface freshwater was retained.

https://www.nature.com/articles/s41558-018-0105-1

[Blessed Weather]

According to a new study published in the journal Nature, the AMOC has slowed by about 15 percent since the mid-20th century and is now running at its slowest in 1,500 years, with implications for European weather. Extracts:

Observed fingerprint of a weakening Atlantic Ocean overturning circulation

We have identified a characteristic SST fingerprint of an AMOC slow-

down on the basis of high-resolution model simulations. The finger-

print consists of a cooling in the subpolar gyre region due to reduced

heat transport, and a warming in the Gulf Stream region due to a north-

ward shift of the Gulf Stream. This fingerprint is most pronounced

during winterand spring, and itis found in the observed long-term

temperature trends, indicating a pronounced weakening of the AMOC

since the mid-twentieth century.

The AMOC weakening may already have an impact on weather in

Europe. Cold weather in the subpolar Atlantic correlates with high

summer temperatures over Europe, and the 2015 European heat wave

has been linked to the record ‘cold blob’ in the Atlantic that year

Model simulations further suggest that an AMOC weakening could become

the “main cause of future west European summer atmospheric circulation changes”,
as well as potentially leading to increased storminess in Europe.

Full report: here

 

[knocker]

 

Edited May 10, 2018 by knocker

[knocker]

 

Edited May 11, 2018 by knocker

[Singularity]

Interesting that an anomalously strong subtropical high reflects La Nina forcing, yet La Nina years are known to support active hurricane seasons.

This implies to me that the lower wind shear associated with La Nina is the dominant factor of the two, though perhaps with the location of disturbances favoured to be more Caribbean/GOM /western Subtropical N. Atlantic relative to Cape Verde/Main Development Region.

A year like this one that's on the way out of La Nina could therefore prove a recipe for a suppressed hurricane season, as you get the cooling SSTs but not the lower wind shear. On the other hand, unless an El Nino develops sooner than expected, wind shear is unlikely to be anomalously high either - no probably not a particularly quiet season favoured, just not particularly active either.

Just speculation, mind! I have seen forecasts based solely on these factors fall flat on their face before; there's more to consider (but I risk giving too much away then!).

[summer blizzard]

20 hours ago, Singularity said:

Interesting that an anomalously strong subtropical high reflects La Nina forcing, yet La Nina years are known to support active hurricane seasons.

This implies to me that the lower wind shear associated with La Nina is the dominant factor of the two, though perhaps with the location of disturbances favoured to be more Caribbean/GOM /western Subtropical N. Atlantic relative to Cape Verde/Main Development Region.

A year like this one that's on the way out of La Nina could therefore prove a recipe for a suppressed hurricane season, as you get the cooling SSTs but not the lower wind shear. On the other hand, unless an El Nino develops sooner than expected, wind shear is unlikely to be anomalously high either - no probably not a particularly quiet season favoured, just not particularly active either.

Just speculation, mind! I have seen forecasts based solely on these factors fall flat on their face before; there's more to consider (but I risk giving too much away then!).

Although Nina does support a stronger than normal sub-tropical high it's definitely not the norm to cool the Atlantic as a result so i suspect what usually happens is that once we get to early summer and everything shifts north, any enhanced trades during winter/early spring also shift and so by August-October the MDR is nice and warm albeit the impact of shear vs SST's is interesting. 

As i posted in the hurricane season thread the North Tropical Atlantic values are consistent with developing Nino seasons in 2014, 2015, 2012 and 2009 although of course, two of those flopped.  

[damianslaw]

Note we have yet again a notably cool north atlantic and a warmer zone around the azores, which combined is likely to result in an active jet stream thanks to the pronounced temp profile marked difference. Are we to see yet another NW-SE split summer which becomes progressively wetter as it wears on... with best conditions for the NW reserved for May and June.. mmm we've been here so many times these past few years.

[Singularity]

With the right forcing from the tropics, that active jet could be diverted north of us. We managed that May-June last year but then the tropics changed tune and as you say, things took a turn for the worse. I recommend checking out this afternoon's MOD thread post from Tamara for more information on this .