Observations of coupling between surface wind stress and sea surface temperature in the eastern tropical Pacific

Satellite measurements of surface wind stress from the QuikSCAT scatteromet er and sea surface temperature (SST) from the Tropical Rainfall Measuring M ission Microwave Imager are analyzed for the three-month period 21 July-20 October 1999 to investigate ocean-atmosphere coupling in the eastern tropic al Pacific. Oceanic tropical instability waves (TIWs) with periods of 20-40 days and wavelengths of 1000-2000 km perturb the SST fronts that bracket b oth sides of the equatorial cold tongue, which is centered near 1 degreesS to the east of 130 degreesW. These perturbations are characterized by cusp- shaped features that propagate systematically westward on both sides of the equator. The space-time structures of these SST perturbations are reproduc ed with remarkable detail in the surface wind stress field. The wind stress divergence is shown to be linearly related to the downwind component of th e SST gradient with a response on the south side of the cold tongue that is about twice that on the north side. The wind stress curl is linearly relat ed to the crosswind component of the SST gradient with a response that is a pproximately half that of the wind stress divergence response to the downwi nd SST gradient. The perturbed SST and wind stress fields propagate synchro nously westward with the TIWs. This close coupling between SST and wind str ess supports the Wallace et al. hypothesis that surface winds vary in respo nse to SST modification of atmospheric boundary layer stability.