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chrisbell-nottheweatherman

El Nino and Euro high

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Given the recent references in the model discussion thread regarding the effect on the weather in the UK of the vortex sitting over Greenland, which I imagine is related to El Nino via. its effects on the vortex, I find myself wondering whether El Nino can explain the seemingly unmovable Euro high.  Is there any research that supports my speculation?

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11 hours ago, chrisbell-nottheweatherman said:

Given the recent references in the model discussion thread regarding the effect on the weather in the UK of the vortex sitting over Greenland, which I imagine is related to El Nino via. its effects on the vortex, I find myself wondering whether El Nino can explain the seemingly unmovable Euro high.  Is there any research that supports my speculation?

If one would be able to explain the abundance of high pressure over the European Continent with El Nino alone, we would be able to make excellent seasonal forecasts of the weather in Europe only by the presence or absence of El Nino alone. Unfortunately, this is not the case. So, the short answer is no, there is no evidence supporting your claim.

But there is of course much more going on behind the scenes, as I will try to show in the long answer versionJ.

Was a European high present during El Nino?

Before going into detail, it is good to investigate whether high pressure activity has indeed been dominating the scene. Here I focus on the period September-November. See below:

pfall.thumb.png.96bed8411e2bfce819c21ee5

500 hPa heights between September and November. Created with ESRL.

Note that these are geopotential heights at 500 hPa, and not the anomalies (for clarity reasons). Higher heights roughly indicate higher pressure. The isolines (lines of equal height) are pointing northward over Europe, which means high pressure activity is dominating the scene. In other words, the isolines are anticyclonically curved, which is another way to say the same. So yes, high pressure has indeed been dominating the scene during autumn.

A wealth of factors cooperating

For further explanation, it is important to understand why it is not possible to explain for example the presence of weather phenomenon A (e.g. the Euro high) with another phenomenon (e.g. El Nino). Let us focus on the European high pressure area for now.

If we would like to explain why there is so much high pressure over the European Continent, we have to take into account a wealth of factors. For example, how does such a high pressure area develop? And from this, you could raise the following questions: What is the influence of Atlantic sea surface temperatures on the presence of high pressure over Europe? What is the effect of El Nino on the presence of high pressure over Europe? What is the influence of stratospheric conditions on...?

As you see from this example, there are many factors which could contribute to the presence of anomalous high pressure over Europe during the last few months. And the worst is: they are all interlinked as well, and in a very irregular fashion. This complex interaction between these factors makes it very difficult to explain for example the presence of high pressure above Europe.

Lights in the woodshed

Still, even though we live in a very complex world, we can still predict some things in the far future. Think of the effects of El Nino on US weather, which are relatively well documented. So there is a possibility to explain certain patterns with El Nino.

The distance issue

We can predict the weather in a few months over the US to a reasonable degree when we know the state of ENSO (whether we have El Nino or La Nina). However, unfortunately this does not apply for Europe. One of the reasons is that the direct effects of El Nino on the weather in the midlatitudes do not reach as far in a consistent fashion. The reasoning behind this is very interesting, but it is also highly complex. In short, too many factors are interacting with the El Nino effect to cause a clear and persistent pattern over Europe.

The scientific part of the story

In science, it is also well known that the presence of El Nino does not have a clear-cut effect on the weather of Europe. Some research suggests some pressure patterns are more likely to occur in certain months in winter during an El Nino, but these patterns do not correspond to the current pattern we are observing. See the link below for the article about this pressure pattern-ENSO relationship.

http://onlinelibrary.wiley.com/doi/10.1002/joc.890/full

Uncharted territory and Polar Vortex definition issues

To finalize, there are a few cautionary notes that are worth mentioning.

1)      The El Nino we are observing today is stronger than ever before since at least 1980, which means that we are currently in uncharted territory. As a result, it is more difficult to anticipate the effects of El Nino on the weather in the midlatitudes, even in the US.

2)      The term Polar Vortex is a term that is often misused. In short, there are two ‘types’ of polar vortices which are interlinked. The first is located in the stratosphere, and is thereby the stratospheric polar vortex. This polar vortex is almost always present in the Northern Hemispheric winter, and is often centered near the North Pole. The tropospheric polar vortex, on the other hand, is located in the troposphere. It consists much less often out of one entity (it could have multiple centers spread throughout the high latitudes). These terms should not be confused.

3)      The link of ENSO on both polar vortices is to my knowledge rather uncertain, and therefore it is even hard to draw any conclusions about this relationship. Perhaps the stratospheric polar vortex does have a clear link with El Nino. Maybe somebody else knows more about this linkage?

Concluding note

Concluding, lots can be said about such teleconnections, as they are called. It never ceases to amaze how warmer sea surface temperatures in the Pacific consistently cause certain weather patterns in the US (and other parts in the world). Although we know quite a bit about them, there is much to be learned about their occurrence and their physical background. I hope this explanation, although maybe a bit extensive, helps clarifying why it is not possible to make conclusions about the statement you gave. If anything is not clear, just ask!

 

 

 

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Thanks.  I'm getting the impression that even my assumptions regarding ENSO and the Stratospheric vortex are not as cut-and-dried as I thought.  I based this assumption of the following blog article from our own Nick Finnis and from our winter forecast, in particular, the section entitled "ENSO Conclusions":

http://www.netweather.tv/index.cgi?action=news;storyid=6991;sess=

http://www.netweather.tv/index.cgi?action=winter-forecast-2015;sess=

I presume that factors such as Eurasian snow cover and the QBO are much more predictive in terms of vortex strength than ENSO?  As regards the Euro high anomaly, it's interesting to note that data confirms my impression that autumn has been dominated by the Euro high.  Its influence can be seen even by an ignoramus like me in the outputs posted in the model discussion thread, in that it's combining with the Greenland tropospheric vortex lobe to generate a south-westerly feed over Western Europe including the UK.  I never asserted with any degree of confidence that ENSO could have been influencing the anomalous heights over the continent, but I just wondered whether it could be a factor.  By the sounds of it, the concurrently-observed lingering presence of the Euro high and the strong El nino may be coincidental?

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