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
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