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the whole basis of 'The Day After Tomorrow' was the rapid decline of the AMOC...

just saying...

 

Lol True, but I think they holywood - ed it up. There's no way that could happen in that time frame?? If the AMOC came to a grinding halt, would we get a climate more suited to our latitude, or would the Jet Stream still keep things temperate?

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So, have you ever wondered how exactly would N Atlantic look like if you would pump out all the water? Well, its one big mountain range (MAR - Mid Atlantic Ridge). It gives you a feeling and a differe

Yeah, I think that's quite a disingenuous chart (no reflection on yourself , of course!).   If we look at the months used in that chart, and the 9 months leading up to them, we get the following:  

The 13 hours later this arrived..   Many thanks for your enquiry regarding North Atlantic sea surface temperatures. I have spoken to the relevant scientists within the Met Office Hadley Centre who h

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Lol True, but I think they holywood - ed it up. There's no way that could happen in that time frame?? If the AMOC came to a grinding halt, would we get a climate more suited to our latitude, or would the Jet Stream still keep things temperate?

A large cold pool in the Atlantic was very common in the 80's. This is nothing new.

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Lol True, but I think they holywood - ed it up. There's no way that could happen in that time frame?? If the AMOC came to a grinding halt, would we get a climate more suited to our latitude, or would the Jet Stream still keep things temperate?

That would depend on the strength of the polar cell and whether a weakened polar cell expanded somewhat. The AMOC is an intergral part of the dynamical system on our half of the earth and will definitely have some bearing, but then so will the Ice growth and any effect any melting has on salinity. All of a sudden there are a lot of balls in the pot and working it out becomes less easy.

 

I have been reading about the progression of AMO phases and how there is a trend for a more negative NAO as we progress through the back end of a warm phase ( and vice versa for a cold phase) but more reading needed prior to working out anything substantial for this winter. The EN and +PDO are normally conducive to a wetter winter in central Europe. The question remains whether any persisting Atlantic cold pool can disrupt that at all.

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That's outrageous. I guess it's no coincidence then that the extreme winters of 09 and 10 coincided with this event.

 

This winter is going to be interesting what ever happens. The strong El Nino coupled with the cold North Atlantic could really disrupt the jet stream. 

 

F1.large.jpg

 

 

 

You should go back through the whole thread, there's a ton of information from Blessed Weather, Nouska, BornFromTheVoid, et al.

 

For what it's worth, I'm not persuaded that a cold North Atlantic anomaly = cold UK winter for this year. However, if we really are witnessing a secular change in the North Atlantic conveyor - whether as part of the AMO phase, or forced, or both - then the next few years may not be without interest.

 

Edit: I would also thoroughly recommend spending some time at the excellent RAPID website http://www.rapid.ac.uk/background.php

It's at the cutting edge of climate science fieldwork. As Nouska noted above, the next data collection cruise is scheduled for this October, but I doubt the results will appear in the scientific literature until next year. However, the National Oceanography Centre are developing a system to generate real-time data from the array in collaboration with RAPID.

 

http://noc.ac.uk/news/amoc-amok

 

Currently data from the RAPID observational array at 26ËšN in the Atlantic is collected every 18 months. However, researchers at the NOC are now testing a new system that will enable data to be collected in near real-time via a satellite link to shore. This may allow RAPID data to be used in seasonal forecasts of weather and sea-level changes. For example, the 2009/10 slowdown of the AMOC caused sea levels in New York to rise by 13cm, which led to flooding and beach erosion on a scale similar to that from a hurricane. If scientists had had access to real-time RAPID data in 2009 potentially they could have predicted this event up to two months in advance.

 

This link may also be of interest to those brave enough to some data analysis themselves:

 

http://www.bodc.ac.uk/rapidmoc/data/

Edited by Yarmy
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That's outrageous. I guess it's no coincidence then that the extreme winters of 09 and 10 coincided with this event.

 

This winter is going to be interesting what ever happens. The strong El Nino coupled with the cold North Atlantic could really disrupt the jet stream. 

 

As of last year, the scientists were still unsure of what cause the steep drop in the AMOC. All I'll contribute is that it will be interesting to see if a similar event occurs at next solar minimum.

 

Paper discussing the episode    http://www.ocean-sci.net/10/683/2014/os-10-683-2014.pdf

 

A screenshot of discussion for  those with no time to read in full.

 

ZNQ9fkx.png

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Lol True, but I think they holywood - ed it up. There's no way that could happen in that time frame?? If the AMOC came to a grinding halt, would we get a climate more suited to our latitude, or would the Jet Stream still keep things temperate?

 

The onsets of both the Younger Dryas and 8.2kyr events occurred over a period of a few decades or perhaps even a few years. The transition back to warm conditions was even faster.

 

http://www.esd.ornl.gov/projects/qen/transit.html

 

For the avoidance of doubt, I'm pretty sure that's not about to happen.  :good:

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I’ve just been catching up with this thread; there are quite some interesting thoughts and contributions about this matter. Great to see this all being collected in this thread.

 

The atmospheric angular momentum – although I understand the general concept – is still too difficult to get my head around, but I think this will improve over the course of the year with some extra study and reading contributions on this site.

 

What piqued my interest is the relationship between the cooler-than-average sea surface temperatures in the Atlantic and lower geopotential heights there. In fact, this could even be related to the extraordinarily high temperatures on the European mainland.

 

Cooler than average sea surface temperatures in the Atlantic and low pressure activity

 

For the analysis I am going to use climate composites of last summer (2015).

 

As the name of the thread suggests, the SSTS in the central Atlantic are much cooler than normal.

 

post-20885-0-14416500-1442954328_thumb.p

Sea surface temperature anomalies between June and August, 2015. Courtesy: NOAA.

 

As many of us have noted during past summer, a frequent occurrence during last summer was the presence of a 500 hPa trough located on average just to the northwest of Iceland. This translated to a negative anomaly in heights over that very same area:

 

post-20885-0-87793600-1442954322_thumb.p

Geopotential height anomalies between June and August, 2015. Courtesy: NOAA.

 

This area completely overlaps with the negative sea surface temperatures just west of Europe. Coincidence? Most likely not, but I do not yet get why cooler than normal SSTS would relate to lower than average heights. What I thought is that cooler than normal surface temperatures are related to descending motions, and as a result more high pressure activity. Any explanation would be greatly appreciated!

 

What does this have to do with the European heat?

 

An interesting question is how the aforementioned troughing (and associated low pressure activity) relates to the heat wave in central Europe. For that purpose, we look at the geopotential height anomalies once again:  

 

post-20885-0-54236700-1442954325_thumb.p

Geopotential height anomalies between June and August, 2015. Courtesy: NOAA.

The answer lies in the part ahead of this troughing. Because this troughing was so persistent and deep, a continuous supply of very warm African air was pumped up northeastward on the southeastern flank of this troughing.

 

A final small contribution

 

Finally, it is also nice to look at longitude-height cross sections. This figure is tough to interpret, though.

 

post-20885-0-52274400-1442954320_thumb.p

Cross section of geopotential height anomalies between 50E and 50W, at 50 N between June and August.

 

What we see here is that between 40W and 20W, there is a clear negative height anomaly (lower than average pressure). This negative height anomaly is directly superimposed over the colder than average SSTS over the Atlantic.

 

On the other side, we see the much higher heights (higher than average  pressure between 10 and 50E, which is roughly the area where the European heat wave has manifested itself.

 

Summary

 

In this post we have seen that cooler than average sea surface temperatures over the North Atlantic could (at least partially) explain the heat wave across Europe. There remains much more to be revealed about last summer of course, which could even have implications for our winter! But that is for another time J.

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I’ve just been catching up with this thread; there are quite some interesting thoughts and contributions about this matter. Great to see this all being collected in this thread.

 

The atmospheric angular momentum – although I understand the general concept – is still too difficult to get my head around, but I think this will improve over the course of the year with some extra study and reading contributions on this site.

 

What piqued my interest is the relationship between the cooler-than-average sea surface temperatures in the Atlantic and lower geopotential heights there. In fact, this could even be related to the extraordinarily high temperatures on the European mainland.

 

Cooler than average sea surface temperatures in the Atlantic and low pressure activity

 

For the analysis I am going to use climate composites of last summer (2015).

 

As the name of the thread suggests, the SSTS in the central Atlantic are much cooler than normal.

 

attachicon.gifSST_anoms.png

Sea surface temperature anomalies between June and August, 2015. Courtesy: NOAA.

 

As many of us have noted during past summer, a frequent occurrence during last summer was the presence of a 500 hPa trough located on average just to the northwest of Iceland. This translated to a negative anomaly in heights over that very same area:

 

attachicon.gifGPH.png

Geopotential height anomalies between June and August, 2015. Courtesy: NOAA.

 

This area completely overlaps with the negative sea surface temperatures just west of Europe. Coincidence? Most likely not, but I do not yet get why cooler than normal SSTS would relate to lower than average heights. What I thought is that cooler than normal surface temperatures are related to descending motions, and as a result more high pressure activity. Any explanation would be greatly appreciated!

 

What does this have to do with the European heat?

 

An interesting question is how the aforementioned troughing (and associated low pressure activity) relates to the heat wave in central Europe. For that purpose, we look at the geopotential height anomalies once again:  

 

attachicon.gifGPH_EDIT.png

Geopotential height anomalies between June and August, 2015. Courtesy: NOAA.

The answer lies in the part ahead of this troughing. Because this troughing was so persistent and deep, a continuous supply of very warm African air was pumped up northeastward on the southeastern flank of this troughing.

 

A final small contribution

 

Finally, it is also nice to look at longitude-height cross sections. This figure is tough to interpret, though.

 

attachicon.gifCross_GPH.png

Cross section of geopotential height anomalies between 50E and 50W, at 50 N between June and August.

 

What we see here is that between 40W and 20W, there is a clear negative height anomaly (lower than average pressure). This negative height anomaly is directly superimposed over the colder than average SSTS over the Atlantic.

 

On the other side, we see the much higher heights (higher than average  pressure between 10 and 50E, which is roughly the area where the European heat wave has manifested itself.

 

Summary

 

In this post we have seen that cooler than average sea surface temperatures over the North Atlantic could (at least partially) explain the heat wave across Europe. There remains much more to be revealed about last summer of course, which could even have implications for our winter! But that is for another time J.

What does lower geopotential height mean?

Just how cold is the Atlantic compared to normal at the moment?

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What does lower geopotential height mean?

Just how cold is the Atlantic compared to normal at the moment?

 

Upper air charts such as the 500mb are contour charts and are drawn up using lines of equal geopotential height known as isohypse. These represent a constant pressure surface so no matter what the value of them they always represent 500mb. Without going in to how they are calculated a rule of thumb would be the lower the geopotential height, the lower the 500mb level, the cooler the air. They can be used to identify troughs and ridges as the heights will be lower with the former and higher with the latter.

 

P.S

Geopotential height is the distance above the earth's surface if it was a perfect and  flat sphere.

 

EDIT

 

I've slightly adjusted the P.S. so it makes slightly better sense/

 

An example. Don't worry about the anomaly bit. Blue indicate troughs (LP) and red/orange ridges (HP). The heights are in decametres.so X 10 for geopotential metres.

post-12275-0-05192600-1442985369_thumb.p

Edited by knocker
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Upper air charts such the 500mb are contour charts are drawn up using lines of equal geopotential height known as isohypse. These represent a constant pressure surface so no matter what the value of them they always represent 500mb. Without going in to how they are calculated a rule of thumb would be the lower the geopotential height, the lower the 500mb level, the cooler the air. They can be used to identify troughs and ridges as the heights will be lower with the former and higher with the latter.

 

P.S

Geopotential height is the distance above the earth's surface if it was a perfect and  flat sphere.

 

EDIT

 

I've slightly adjusted the P.S. so it makes slightly better sense/

 

An example. Don't worry about the anomaly bit. Blue indicate troughs (LP) and red/orange ridges (HP). The heights are in decametres.so X 10 for geopotential metres.

Thank you for this excellent explanation.
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" Most likely not, but I do not yet get why cooler than normal SSTS would relate to lower than average heights. What I thought is that cooler than normal surface temperatures are related to descending motions, and as a result more high pressure activity. Any explanation would be greatly appreciated!"

 

I think what you say about lower SSTs being associated with higher pressure will hold true in the tropics where the weather is convective in nature. Of course across the North Atlantic, the weather is dominated by mid latitude depressions created by a mixing of warm and cold air masses. If you have a large body of water with less energy than normal, then I would expect the warm sectors in depressions to be less strong due to the lack of energy in the ocean - meaning the depressions won't drive so far north as they develop. I think that could translate to more southerly jet - keeping the low pressure zones a bit further south - and creating the below average pressure anomaly.  It's chicken and the egg though isn't it - did the SSTs cause the pressure anomaly - or the other way around?!  

 

Would be great if one of the active or retired professional meteorologists could comment as I'd like to know if I'm barking up the right tree or not and either way they'll explain it better than me.

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" Most likely not, but I do not yet get why cooler than normal SSTS would relate to lower than average heights. What I thought is that cooler than normal surface temperatures are related to descending motions, and as a result more high pressure activity. Any explanation would be greatly appreciated!"

 

I think what you say about lower SSTs being associated with higher pressure will hold true in the tropics where the weather is convective in nature. Of course across the North Atlantic, the weather is dominated by mid latitude depressions created by a mixing of warm and cold air masses. If you have a large body of water with less energy than normal, then I would expect the warm sectors in depressions to be less strong due to the lack of energy in the ocean - meaning the depressions won't drive so far north as they develop. I think that could translate to more southerly jet - keeping the low pressure zones a bit further south - and creating the below average pressure anomaly.  It's chicken and the egg though isn't it - did the SSTs cause the pressure anomaly - or the other way around?!  

 

Would be great if one of the active or retired professional meteorologists could comment as I'd like to know if I'm barking up the right tree or not and either way they'll explain it better than me.

Good post Beng. I have some maritime magazines stored away somewhere that provided interesting reports about the ( cold decade over the sub zonal Arctic waters of the North Atlantic in the 1960s ) These were published in the early 1970s and some referred about the pressure anomalies more widely over the North Atlantic. When I find them I will get back with an insight to the thoughts at that time. Maybe no relation to current the situation but could be worth another view point.

 C

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" Most likely not, but I do not yet get why cooler than normal SSTS would relate to lower than average heights. What I thought is that cooler than normal surface temperatures are related to descending motions, and as a result more high pressure activity. Any explanation would be greatly appreciated!"

 

I think what you say about lower SSTs being associated with higher pressure will hold true in the tropics where the weather is convective in nature. Of course across the North Atlantic, the weather is dominated by mid latitude depressions created by a mixing of warm and cold air masses. If you have a large body of water with less energy than normal, then I would expect the warm sectors in depressions to be less strong due to the lack of energy in the ocean - meaning the depressions won't drive so far north as they develop. I think that could translate to more southerly jet - keeping the low pressure zones a bit further south - and creating the below average pressure anomaly.  It's chicken and the egg though isn't it - did the SSTs cause the pressure anomaly - or the other way around?!  

 

Would be great if one of the active or retired professional meteorologists could comment as I'd like to know if I'm barking up the right tree or not and either way they'll explain it better than me.

 

I am going to sit this out as it is a long time since I was actively involved and my memory is not what it used to be. You do raise some interesting points, perhaps if Jo reads this she may answer for us. Perhaps those that have recently done their Meteorology degrees also?

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" Most likely not, but I do not yet get why cooler than normal SSTS would relate to lower than average heights. What I thought is that cooler than normal surface temperatures are related to descending motions, and as a result more high pressure activity. Any explanation would be greatly appreciated!"

 

I think what you say about lower SSTs being associated with higher pressure will hold true in the tropics where the weather is convective in nature. Of course across the North Atlantic, the weather is dominated by mid latitude depressions created by a mixing of warm and cold air masses. If you have a large body of water with less energy than normal, then I would expect the warm sectors in depressions to be less strong due to the lack of energy in the ocean - meaning the depressions won't drive so far north as they develop. I think that could translate to more southerly jet - keeping the low pressure zones a bit further south - and creating the below average pressure anomaly.  It's chicken and the egg though isn't it - did the SSTs cause the pressure anomaly - or the other way around?!  

 

Would be great if one of the active or retired professional meteorologists could comment as I'd like to know if I'm barking up the right tree or not and either way they'll explain it better than me.

 

A paper looking at how changes in the AMOC can influence the zones of baroclinicity and storm tracks.

 

http://centaur.reading.ac.uk/28408/1/mocstorms_natgeo.pdf

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Apologies if this has been posted before.     I found it quite an interesting read.

Not too sure what to think, as given the article is from the Washington Post which I believe is a staunch supporter of President Obama's Climate Change agenda. and therefore may be purely for  political purposes?

However, If it is a true reflection of the current situation, it really looks quite stunning and, as touched on in the article, that the Atlantic Conveyor may indeed be slowing down abruptly after all, makes the possible ramifications rather interesting?

Wondered what peoples' thoughts were?

 

 

http://www.washingtonpost.com/news/energy-environment/wp/2015/09/24/why-some-scientists-are-worried-about-a-surprisingly-cold:

Edited by Blitzen
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Apologies if this has been posted before.     I found it quite an interesting read.

Not too sure what to think, as given the article is from the Washington Post which I believe is a staunch supporter of President Obama's Climate Change agenda. and therefore may be purely for  political purposes?

However, If it is a true reflection of the current situation, it really looks quite stunning and, as touched on in the article, that the Atlantic Conveyor may indeed be slowing down abruptly after all, makes the possible ramifications rather interesting?

Wondered what peoples' thoughts were?

 

 

http://www.washingtonpost.com/news/energy-environment/wp/2015/09/24/why-some-scientists-are-worried-about-a-surprisingly-cold:

I just think it's the naturally occurring gradual switch over of the AMO cycle to cold which should be expected to occur over the next 5 years or so.

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I just think it's the naturally occurring gradual switch over of the AMO cycle to cold which should be expected to occur over the next 5 years or so.

Indeed and all this talk of causations is rather silly when looking through the archives of the AMO.

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