We quantify the atmospheric component of El Niño using the Equatorial Southern Oscillation Index ( EQSOI) and the Southern Oscillation Index ( SOI), both of which compare the surface atmospheric pressure in the western Pacific to that in the eastern Pacific (more details on these indexes here). Convection over Indonesia was reduced, too, another characteristic of the weaker Walker circulation. Over the past month, evidence of the weakened Walker circulation appeared in the form of weaker trade winds over the western Pacific and more clouds and rain over the equatorial Pacific. Anomalous ocean warming in the central and eastern Pacific (orange) help to shift a rising branch of the Walker Circulation to east of 180°, while sinking branches shift to over the Maritime continent and northern South America. Generalized Walker Circulation (December-February) anomaly during El Niño events, overlaid on map of average sea surface temperature anomalies. These strong surface winds help to keep the warm water piled up in the western Pacific. The average Walker circulation is characterized by rising air and storms (convection) over the very warm waters of the far western Pacific, west-to-east winds high up in the atmosphere, descending motion over the relatively cooler waters of the eastern Pacific, and the trade winds-east-to-west surface winds. The third criteria, “indications of a weaker Walker circulation,” refers to the average atmospheric pattern over the equatorial Pacific. We anticipate that it will remain above this El Niño threshold for the next several months, based on climate model predictions and current conditions in the tropical Pacific (more on this in a minute)… check! There are the first two of our three rings criteria. NOAA, based on Coral Reef Watch maps available from NOAA View. A higher-resolution version of this animation is available as a movie. The waters in the key monitoring region, which scientists call "the Niño-3.4 region," start out cooler than average (blue) and progressively become warmer than average (red) as La Niña ends and El Niño arrives. Animation of maps of sea surface temperatures in the Pacific Ocean compared to the long-term average over five-day periods from the end of January to early June 2023.
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