![]() However, for most of the world El Niño is considered to be a more extensive abnormal warming of the equatorial Pacific that has a recognizable signature in the global patterns of atmospheric pressure (e.g., Walker and Bliss 1932 Troup 1965 Berlage 1966 Bjerknes 1966, 1969), atmospheric circulation (e.g., Arkin 1982), precipitation, and temperature (e.g., Caviedes 1973 Hastenrath and Heller 1977 Rasmusson and Carpenter 1983 Bhalme et al. For those in Ecuador and Peru, El Niño is an abnormal warming of the sea surface temperature (SST) along the west coast of South America (e.g., Wyrtki 1975) that is accompanied by a loss of fish revenue and heavy flooding rains (e.g., Nash 2002). There is a great diversity in what El Niño means in many parts of the world. The methodology is quite general and can be used to relate the ENSO cycle to other quantities. The method is illustrated using precipitation in the global Tropics and subtropics and in the conterminous United States. An objective method that relates the EIS to anomalies is used to assess the effects of warm and cold episodes. The Climate Prediction Center’s (CPC’s) monthly Climate Diagnostics Bulletin and ENSO Diagnostic Discussions will serve as the primary vehicles for disseminating real-time information concerning the ENSO alert status to the scientific community and public at large. The intensity scale, referred to as the ENSO Intensity Scale (EIS), is used for operational and retrospective assessments of the intensity of warm (El Niño) and cold (La Niña) episodes, without being prescriptive concerning ENSO-related anomalies or impacts. An advisory is issued when El Niño or La Niña conditions are present, based on NOAA’s operational definitions. A watch is issued when conditions are favorable for the formation of an El Niño or La Niña within the next 6 months. The system includes watches, advisories, and a five-class intensity scale for warm and cold phases of the ENSO cycle. Precipitation anomalies are with respect to the 1979–95 base period.Īn alert classification system for the ENSO cycle is introduced. To be consistent with the ONI, 3-month running-mean values are shown in both (b) and (c). The mean value of the TPI for the period (47.5%) is indicated by the horizontal line. (c) Evolution of the TPI since 1979, defined as the 3-month running-mean sum of the fractional areas of the global Tropics and subtropics with precipitation anomalies above the 70th percentile and below the 30th percentile. The mean value for the period (indicated by the horizontal line) is within a few hundredths of 25% for both time series. Green (brown) shading indicates periods when areal coverage is greater for precipitation anomalies above the 70th percentile (below the 30th percentile). ![]() ![]() (b) Time series of the fractional area of the global Tropics and subtropics (30°S–30°N) with precipitation anomalies above the 70th percentile (solid) and below the 30th percentile (dashed), based on percentiles in the gamma distribution. ![]()
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