Ranking the strongest ENSO events while incorporating SST uncertainty

Abstract

Abstract The strength of El Niño–Southern Oscillation (ENSO) is often measured using a single, discrete value of the Niño index. However, this method does not consider the sea surface temperature (SST) uncertainty associated with the observations and data processing. On the basis of the Niño3.4 index and its uncertainty, we find that the strength of the three strongest ENSO events is not separable at 95% confidence level. The monthly peak SST anomalies in the most recent 2015–2016 El Niño is tied with 1997–1998 and 1982–1983 El Niño as the strongest. The three most negative monthly Niño values occur within the 1955–1956, 1973–1974, and 1975–1976 La Niña events, which cannot be discriminated by rank. The histograms of 1000‐member ensemble analysis support the conclusion that the strength of the three strongest ENSO events is not separable. These results highlight that the ENSO ranking has to include the SST uncertainty.