AGU citation: Kessler, W. S., Is ENSO a cycle or a series of events?, Geophys. Res. Lett., 29(23), 2125, doi:10.1029/2002GL015924, 2002
After early ideas that saw ENSO as an isolated event, the advent of coupled models brought the conception of ENSO as a cycle in which each phase led to the next in a self-sustained oscillation. Twenty-two years of observations that represent the El Niño and La Niña peaks (east Pacific SST) and the memory of the system (zonal mean warm water volume) suggest a distinct break in the cycle, in which the coupled system is able to remain in a weak La Niña state for up to two years, so that memory of previous influences would be lost. Similarly, while the amplitude of the anomalies persists from the onset of a warm event through its termination, there is no such persistence across the La Niña break. These observations suggest that El Niños are in fact event-like disturbances to a stable basic state, requiring an initiating impulse not contained in the dynamics of the cycle itself.
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Dr. William S. Kessler
NOAA / PMEL / OCRD
7600 Sand Point Way NE
Seattle WA 98115 USA
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