A Relationship between Interannual Variations in the South Pacific Wind Stress Curl, the Indonesian Throughflow, and the West Pacific Warm Water Pool

Roxana C. Wajsowicz Oceans and Ice Branch, NASA/Goddard Space Flight Center, Greenbelt, Maryland

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Abstract

Simple theory gives that the depth-integrated flow between the Pacific and Indian Oceans, on interannual timescales and longer, is driven by the integral of the wind stress along a line from the northern tip of Papua–New Guinea across the equatorial Pacific, south along the South American west coast, westward across the South Pacific at the latitude of the southern tip of Australia, and northward along the west coast of Australia. Evaluation of this integral using ECMWF/JMA 1000-mb wind data for the decade 1980–89 yields an interdecadal and interannual signal. The interannual signal peaks in 1981 and 1985, then decreases sharply through the ensuing ENSO events. The variations are chiefly attributable to variations in the integral of wind stress across the midlatitude line in the South Pacific. The presence of the shallow sills within the Indonesian seas will partially block the midlatitude contribution, but local baroclinic adjustment over the sills will reduce the blocking effect and produce a corresponding interannual variation in upper-layer transport through the seas. Two mechanisms by which variations in throughflow magnitude could contribute to warm water pileup in the west Pacific are proposed.

Abstract

Simple theory gives that the depth-integrated flow between the Pacific and Indian Oceans, on interannual timescales and longer, is driven by the integral of the wind stress along a line from the northern tip of Papua–New Guinea across the equatorial Pacific, south along the South American west coast, westward across the South Pacific at the latitude of the southern tip of Australia, and northward along the west coast of Australia. Evaluation of this integral using ECMWF/JMA 1000-mb wind data for the decade 1980–89 yields an interdecadal and interannual signal. The interannual signal peaks in 1981 and 1985, then decreases sharply through the ensuing ENSO events. The variations are chiefly attributable to variations in the integral of wind stress across the midlatitude line in the South Pacific. The presence of the shallow sills within the Indonesian seas will partially block the midlatitude contribution, but local baroclinic adjustment over the sills will reduce the blocking effect and produce a corresponding interannual variation in upper-layer transport through the seas. Two mechanisms by which variations in throughflow magnitude could contribute to warm water pileup in the west Pacific are proposed.

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