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Research on new El Nino measurement index.


Evo

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Posted
  • Location: Bournemouth
  • Location: Bournemouth

    A while ago, there was an interesting piece of research posted over on easternuswx.com:

    http://www.easternuswx.com/bb/index.php?showtopic=140902

    The theory is that subsurface thermocline anomolies play the driving role in determining the El Nino/La Nina state, rather than the conventional opinion that it is boundary layer interactions being the dominant factor.

    It's well worth a read and I'm interested to hear what some of Net Weather's experts think about this.

    I think I'm right in saying that if this was the case, we could've actually been in a La Nina phase for the last couple of months. The disparity between surface waters (end hence ENSO index) and the observed weak Nina pattern being explained by the wild negative GLAAM index?

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    Posted
  • Location: Coventry,Warwickshire
  • Location: Coventry,Warwickshire

    El nino and la nina can be compared to blowing across the top of the froth on top of a cup of coffee. Blow one way and the coffee (cooler water) is exposed, stop blowing and the froth (warm water) seeps back to cover the whole. Anything below the surface of the water can have little physical bearing on the weather patterns above so the link is not correct. What is true is that the depth of warm water (depth of the thermocline) can have bearing on how close the la nina or el nino conditions are. Using our analogy if the froth is not very deep then a quick blow across the surface will expose the coffee (cooler water).I don't really agree with the argument that the depth of thermocline is a good indicator of ENSO conditios but I would say it is a good predictor when combined with wind forecasts as to how ENSO conditions will develop. There again maybe I have got the wrong end of the stick so to speak.

    In terms of the GLAAM which is really a measure of the transfer of energy from north to south then I think this is showing that we have had a weaker jet stream pattern than usual. I think this is partly linked to la nina but also to the fact that there has been less continental heat build up this year. Jet streams tend to be strong where cold air meets hot, so cooler tropical air due to cooling from la nina and a late polar vortex break up due to the westerly QBO delaying heat build up have both contributed to the GLAAM being low. There is a link bewteen ENSO and GLAAM but one does not automatically force the other.

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    Posted
  • Location: Bournemouth
  • Location: Bournemouth

    Thanks for the input BF. Your analogy does make a lot of sense!

    The problem I have is not being sufficiently clued up to be able to judge if the case he is making is a valid one (he seems to imply that there's a better corrolation with his index). It does seem logical that atmosphere, surface and deep water are related and interact, so I suppose it comes down to the same old chicken and egg question.

    As for the GLAAM, it seems that everybody has a different opinion as to what it's really saying so it's nice to read a coherent discription that I can understand - much appreciated.

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