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Monthly Oceanic Nino Index (ONI)

The Oceanic Niño Index (ONI) has become the de facto standard that the National Oceanic and Atmospheric Administration (NOAA) uses to identify El Niño (warm) and La Niña (cool) events in the tropical Pacific. It is the three month mean SST anomaly for the El Niño 3.4 region (i.e., 5°N-5°S, 120°-170°W). Events are defined as five consecutive overlapping three month periods at or above the +0.5°C anomaly for warm (El Niño), events and at or below the -0.5 anomaly for cold (La Niña) events. The threshold is further broken down into Weak (with a 0.5 to 0.9 SST anomaly), Moderate (1.0 to 1.4) and Strong (≥ 1.5) events. For an event to be categorized as weak, moderate or strong. it must have equalled or exceeded the threshold for at least three consecutive overlapping three month periods.

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Maintainer 7d7f5f8d-7e3b-483a-8de1-2b122010c1eb
Last Updated June 18, 2019, 17:54 (EDT)
Created June 18, 2019, 17:54 (EDT)