Generalized Walker Circulation (December-February) anomaly during El Niño events, overlaid on map of average sea surface temperature anomalies. The average atmospheric circulation over the tropical Pacific, the Walker circulation, is like a conveyor belt: rising air over the very warm far western Pacific, west-to-east winds high up in the atmosphere, descending air and dry conditions over the east-central Pacific, and returning east-to-west winds near the surface-the trade winds. Social studiesĮl Niño is a coupled phenomenon, meaning the changes we see in the ocean surface temperature must be matched by changes in the atmospheric patterns above the tropical Pacific. If this El Niño were to collapse after hitting this high, dropping back below the threshold of this magnitude before next winter, it would be the first time in our historical record, dating back to 1950. Two is a good start, especially with the 0.8 ☌ recording from May–July. We need to see five consecutive three-month averages above this threshold before these periods will be considered a historical “El Niño episode” and colored red in our ENSO record).

The three-month-average Niño-3.4 Index, the Oceanic Niño Index, was 0.8 ☌ above the long-term mean for the May–July average, the second three-month-period in a row above the El Niño threshold of 0.5 ☌. NOAA image based on a graph by Emily Becker and monthly Niño-3.4 index data from CPC using ERSSTv5.

2-year history of sea surface temperatures in the Niño-3.4 region of the tropical Pacific for all events evolving into El Niño since 1950 (gray lines) and the current event (purple line).

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