COLA Report 17

Model Based Estimates of Equatorial Pacific Wind Stress

Ben P. Kirtman, Edwin K. Schneider, and Bernard Kirtman

August 1995


Abstract

A simple empirical technique for converting the COLA atmospheric model 850 mb zonal winds into a surface stress is described. A Pacific basin version of the GFDL ocean model is used to demonstrate that the atmospheric model winds produce a better simulation of the observed interannual variability in sea surface temperature (SST) than the subjectively analyzed Florida State University (FSU) pseudo wind stress. The atmospheric model winds include interannual variations that pre-date the FSU winds, thus allowing for ocean model diagnostic studies of El Ni¤o and the Southern Oscillation (ENSO) events in the earlier part of this century.

An iterative procedure that assimilates the zonal wind stress based on the simulated SST anomaly errors is also presented. The AGCM wind stress described above serves as the first guess field for the assimilation cycle. The ocean model is used to show how this new wind stress analysis yields a substantially improved simulation of the SST anomalies. Simple experiments with the ocean model show that the improvements in the simulated SST anomalies are associated with a systematic large scale eastward shift in the assimilated wind stress forcing. The success of the assimilation procedure is shown to be independent of ocean model resolution and some evidence is given that indicates that the assimilation procedure works with other ocean models. It is concluded that this new wind stress analysis may be superior to the FSU data and that the iteration procedure provides a simple mechanism for assimilating wind stress anomalies and initializing ocean models for coupled forecasts.


Complete copies of this report are available from:
Center for Ocean-Land-Atmosphere Studies
4041 Powder Mill Road, Suite 302
Calverton, MD 20705-3106
(301) 595-7000
(301) 595-9793 Fax


last update: 31 August 1995
comments to: www@grads.iges.org