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GEOPHYSICAL RESEARCH LETTERS, VOL. 26, NO. 11, PAGES 1593–1596, 1999

On the Termination of El Niño

D. E. Harrison

Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle


Gabriel A. Vecchi

School of Oceanography, University of Washington, Seattle


Abstract

A feature of the end-phase of recent El Niño periods is thermocline shallowing to normal depths, in the central and eastern equatorial Pacific, before sea surface temperature (SST) returns to normal. Also characteristic of El Niño periods is a late-in-the-year shift of the El Niño equatorial westerly wind anomalies, from symmetric about the equator to centered south of the equator. We show that the directly forced ocean response to this shift produces thermocline shallowing like that observed. The wind shift may result from the normal seasonal evolution of Pacific waters warmer than 28°C. These shift from being relatively symmetric about the equator in October-November, to concentrated south of the equator in December-January. Thus, the seasonal cycle may be a central part of the mechanism of El Niño termination.

Received 4 March 1999; accepted 8 April 1999.

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Citation: Harrison, D. E., and G. A. Vecchi (1999), On the Termination of El Niño, Geophys. Res. Lett., 26(11), 1593–1596.