A multi-modal representation of El Niño Southern Oscillation Diversity
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The El Niño-Southern Oscillation (ENSO) is characterized by alternating periods of warm (El Niño) and cold (La Niña) sea surface temperature anomalies (SSTA) in the equatorial Pacific. Although El Niño and La Niña are well-defined climate patterns, no two events are alike. To date, ENSO diversity has been described primarily in terms of the longitudinal location of peak SSTA, used to define a bimodal classification of events in Eastern Pacific (EP) and Central Pacific (CP) types. Here, we use low-dimensional representations of Pacific SSTAs to argue that binary categorical memberships are unsuitable to describe ENSO events. Using fuzzy unsupervised clustering, we recover the four known ENSO categories, along with a fifth category: an Extreme El Niño. We show that Extreme El Niños differ both in their intensity and temporal evolution from canonical EP El Niños. We also find that CP La Niñas, EP El Niños, and Extreme El Niños contribute the most to interdecadal ENSO variability.
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