Upper-ocean response to small-scale wind forcing in the Agulhas Return Current

The upper ocean response to small-scale (100-1000km) features in the wind stress field over the Agulhas Return Current is investigated using the MOM2 general ocean circulation model. The model was forced with steady QuikSCAT scatterometer and National Centers for Environmental Prediction (NCEP) wind stress fields averaged over the 5-yr period August 1999 to July 2004, corresponding to the first 5 complete years of the QuikSCAT observational record. The NCEP surface wind stress field is notably devoid of the small-scale wind features that are evident in the high-resolution QuikSCAT scatterometer observations. These features result from the adjustment of the overlying atmospheric boundary layer to small-scale sea surface temeprature (SST) features, with larger surface stress occuring over warm water and vice versa. The resulting spatial variability in the wind stress field near SST fronts associated with the Agulhas Return Current generate intense and persistent localized wind stress curl patterens in the 5-yr average wind stress fields. Preliminary analyses of the model simulations suggest significant differences in mixed layer depth, particularly along the northern front of the Agulhas Return Current.