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AGU: Geophysical Research Letters

 

Index Terms

  • Oceanography: Physical: El Nino
  • Global Change: Climate dynamics
  • Oceanography: Physical: Air/sea interactions

Abstract

GEOPHYSICAL RESEARCH LETTERS, VOL. 29, 2125, 4 PP., 2002
doi:10.1029/2002GL015924

Is ENSO a cycle or a series of events?

William S. Kessler

NOAA/Pacific Marine Environmental Laboratory, Seattle, Washington, USA

After early ideas that saw El Niños as isolated events, 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 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.

Published 12 December 2002.

Citation: Kessler, W. S. (2002), Is ENSO a cycle or a series of events?, Geophys. Res. Lett., 29(23), 2125, doi:10.1029/2002GL015924.

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