Thursday, February 19, 2015

If this goes on, it'll be hard NOT to call it El Niño

The classic criterion that defines an El Niño event is for the Oceanic Nino Index (ONI) in the Niño 3,4 region to have a sea surface temperature anomaly of +0.5 C or higher for five consecutive overlapping three month periods.

Well, even though the conditions in the Pacific have been uncertain, incipient, and weak, the ONI is 3/5 of the way there.

Cold and Warm Episodes by Season

So here's the last three periods:

SON   0.5

OND   0,7

NDJ   0,7

According to the IRI analysts, the atmosphere, which has been reluctant to do what the atmosphere is supposed to during an El Niño, has been showing some signs of reacting to the warm SST in the Pacific.    And they think there will be neutral to borderline El Niño conditions through April.

And I say if DJF and JFM are +0.5 or above, it's an El Niño.

Looking at the chart at the first link, the 1977-1978 El Niño peaked at +0.8, and only had six periods above 0.5  (0.5, 0.7, 0.8, 0.8, 0.7, 0.5).   The previous year had a similar period.  Both of these are called El Niño.  So despite playing climatic hide-and-seek, we may just get over the El Niño finish line.

The sea will tell.

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