Coupling of Extratropical Mesoscale Eddies in the Ocean to Westerly Winds in the Atmospheric Boundary Layer

Abstract

The sea surface temperature (SST) signature in mesoscale eddies in the western boundary current extensions around the globe and in the Antarctic Circumpolar Current are found to alter the surface stress associated with background westerly winds, producing wind stress curl (WSC) residuals of eddy scale that are capable of modifying the eddy dynamics. This is revealed by examining satellite-derived mesoscale sea level height (SLH), SST, and neutrally stable zonal surface wind (ZSW) residuals together for 18 months. In the presence of background westerly winds on basin scales, warm mesoscale eddies reduce the stability of the marine atmospheric boundary layer, increasing the zonal air?sea momentum flux measured by satellite scatterometry. Warm SST residuals of ?0.8°C are capable of producing westerly ZSW residuals of ?1.2 m s?1 under background westerly winds of ?6 m s?1. Alternatively, this means increasing the otherwise neutrally stable drag coefficient by ?40%, consistent with in situ measurements. The resulting feedback from atmosphere to ocean through the resulting mesoscale WSC residuals (?5.0 ? 10?7 N m?3) produces residual Ekman pumping that can be on the same order as the residual SLH tendency in the eddy field. Moreover, the spatial phasing of the mesoscale WSC residuals acts, on average, to displace the mesoscale eddies equatorward with meridional coupling phase speeds of ?0.01 m s?1 while suppressing their amplitude.