RESPONSES OF THE TROPICAL PACIFIC TO WIND FORCING AS OBSERVED BY SPACEBORNE SENSORS AND SIMULATED BY AN OCEAN GENERAL-CIRCULATION MODEL

In this study, satellite observations, in situ measurements, and model simulations are combined to assess the oceanic response to surface wi nd forcing in the equatorial Pacific. The surface wind fields derived from observations by the spaceborne special sensor microwave imager (S SM/I) and from the operational products of the European Centre for Med ium-Range Weather Forecasts (ECMWF) are compared. When SSM/I winds are used to force a primitive-equation ocean general circulation model (O GCM), they produce 3 degrees C more surface cooling than ECMWF winds f or the eastern equatorial Pacific during the cool phase of an El Nino- Southern Oscillation event. The stronger cooling by SSM/I winds is in good agreement with measurements at the moored buoys and observations by the advanced very high resolution radiometer, indicating that SSM/I winds are superior to ECMWF winds in forcing the tropical ocean. In c omparison with measurements from buoys, tide gauges, and the Geosat al timeter, the OGCM simulates the temporal variations of temperature, st eric, and sea level changes with reasonable realism when forced with t he satellite winds. There are discrepancies between model simulations and observations that are common to both wind forcing fields, one of w hich is the simulation of zonal currents; they could be attributed to model deficiencies. By examining model simulations under two winds, ve rtical heat advection and uplifting of the thermocline are found to be the dominant factors in the anomalous cooling of the ocean mixed laye r.