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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. C3, 3070, doi:10.1029/2002JC001490, 2003

A delayed action oscillator shared by biennial, interannual, and decadal signals in the Pacific Basin

Warren B. White

Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA


Yves M. Tourre

LDEO of Columbia University, Palisades, New York, USA


Mathew Barlow

Atmospheric and Environmental Research, Inc., Lexington, Massachusetts, USA


Mike Dettinger

United States Geological Survey, San Diego, California, USA


Abstract

Biennial, interannual, and decadal signals in the Pacific basin are observed to share patterns and evolution in covarying sea surface temperature (SST), 18°C isotherm depth (Z18), zonal surface wind (ZSW), and wind stress curl (WSC) anomalies from 1955 to 1999. Each signal has warm SST anomalies propagating slowly eastward along the equator, generating westerly ZSW anomalies in their wake. These westerly ZSW anomalies produce cyclonic WSC anomalies off the equator which pump baroclinic Rossby waves in the western/central tropical North Pacific Ocean. These Rossby waves propagate westward, taking ∼6, ∼12, and ∼36 months to reach the western boundary near ∼7°N, ∼12°N, and ∼18°N on biennial, interannual, and decadal period scales, respectively. There, they reflect as equatorial coupled waves, propagating slowly eastward in covarying SST, Z18, and ZSW anomalies, taking ∼6, ∼12, and ∼24 months to reach the central/eastern equatorial ocean. These equatorial coupled waves produce a delayed-negative feedback to the warm SST anomalies there. The decrease in Rossby wave phase speed with latitude, the increase in meridional scale of equatorial SST anomalies with period scale, and the associated increase in latitude of Rossby wave forcing are consistent with the delayed action oscillator (DAO) model used to explain El Niño. However, this is not true of the western-boundary reflection of Rossby waves into slow equatorial coupled waves. This requires modification of the extant DAO model. We construct a modified DAO model, demonstrating how the various mechanisms and the size and sources of their delays yield the resulting frequency of each signal.

Published 13 March 2003.

Index Terms: 4522 Oceanography: Physical: El Nino; 4572 Oceanography: Physical: Upper ocean processes; 4576 Oceanography: Physical: Western boundary currents; 4299 Oceanography: General: General or miscellaneous.

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Citation: White, W. B., Y. M. Tourre, M. Barlow, and M. Dettinger (2003), A delayed action oscillator shared by biennial, interannual, and decadal signals in the Pacific Basin, J. Geophys. Res., 108(C3), 3070, doi:10.1029/2002JC001490.