Comparison of buoy and satellite near-surface wind and sea-surface temperature near ocean fronts

Satellite measurements of near-surface wind stress by the QuikSCAT scatterometer and sea-surface temperature (SST) by the Advanced Microwave Scanning Radiometer on the EOS-Aqua satellite (AMSR-E) have shown a strong and persistent coupling between surface winds and SST over mid-latitude ocean fronts. On the oceanic mesoscale (i.e., spatial scales of roughly 100-1000 km), the surface wind stress increases on warm SST features and decreases over cool SST features, which had been well-documented from numerous previous in situ studies near SST fronts conducted before the launch of these satellites. In this study, these satellite measurements are compared with colocated wind and SST observations from moored ocean buoys. The objectives here are twofold. First, the accuracy of the coupling between surface wind stress and SST is investigated. Secondly, since scatterometers measure surface wind stress rather than the actual surface wind, it is investigated whether the scatterometer-measured surface wind stress response to SST is caused mainly by changes to the actual surface winds, or whether this response is caused by cross-frontal changes in air-sea temperature difference or ocean currents.

To accomplish these goals, moored buoy measurements of surface winds and SST over the Gulf Stream, eastern equatorial Pacific, and U.S. west coast are chosen for this study since these regions have a relatively dense network of buoys located near strong SST frontal zones. From this analysis, it is shown that at most buoy locations, the actual buoy-measured winds respond strongly to SST fronts, and that it is this SST-induced response of the near-surface winds that accounts for most of the SST-induced response of the scatterometer-measured surface wind stress; on average, surface ocean currents and air-sea temperature differences contribute less to the coupling between surface wind stress and SST than does SST-induced changes in the actual surface winds.