2014 El Niño - Now or Not .

By steven d keeler | Jul 10, 2014
Source: NOAA

 

We presently have elevated sea surface temperature anomalies across the equatorial Pacific, what are referred to as El Nino conditions, but the El Nino conditions have not lasted long enough for these conditions to be classified as an “official” El Nino.  -  Bob Tisdale

Historically, scientists have classified the intensity of El Niño based on SST anomalies exceeding a pre-selected threshold in a certain region of the equatorial Pacific. The most commonly used region is the Niño 3.4 region, and the most commonly used threshold is a positive SST departure from normal greater than or equal to + 0.5° C. Since this region encompasses the western half of the equatorial cold tongue region, it provides a good measure of important changes in SST and SST gradients that result in changes in the pattern of deep tropical convection and atmospheric circulation. The criteria, that is often used to classify El Niño episodes, is that five consecutive 3-month running mean SST anomalies exceed the threshold.

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We saw a strong down-welling Kelvin wave this year, which gave ENSO researchers and global warming enthusiasts hope for a strong El Nino. It wasn’t quite as strong as the 1997/98 El Niño but the Kelvin wave was strong enough to draw comparisons.  We’re definitely not seeing a comparative weakening of the trade winds this year, and there have been fewer westerly wind bursts than there were in 1997.  The additional westerly wind bursts and the continued weakening of the trade winds are what drive additional warm water from the western tropical Pacific into the eastern equatorial Pacific, thus reinforcing the development of the El Niño. Those are the additional feedbacks that are absent so far this year.

The El Niño conditions in the sea surface temperatures of the equatorial Pacific are the result of the additional subsurface warm water that had been carried east by the down-welling Kelvin wave. The supply of warmer-than-normal subsurface water is quickly being used up as it is drawn to the surface.   If the trade winds don’t start to weaken and if we don’t see additional westerly wind bursts, the 2014 El Niño will not occur.

Bob Tisdale

 

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