Diagnostic Studies of Pacific Surface Winds

Abstract

Analyses are performed using surface winds derived from the monthly mean FSU Pacific pseudo-stress fields. Vorticity budget calculations reveal the relative contributions of various terms, and allow simplification of the full momentum equations. Based on the simplified equations, a procedure is developed for estimating surface pressure, and then adjusting the winds. The wind field adjustments fall well within the uncertainty of the data, while allowing generally large imbalances in the vorticity budget to be removed completely. Further validation of the procedure is provided by comparisons between estimated and observed pressure anomalies. The adjusted winds and pressure are then used to infer boundary layer and upper level forcing within the context of particular model formulations. These forcing fields an compared with sea surface temperature, outgoing longwave radiation, and highly reflective cloud data in order to infer the dominant mechanisms contributing to observed surface circulation anomalies. It is found that both boundary layer and convective forcing are important. The results show deficiencies in previous model parameterizations based primarily on sea surface temperature and suggest that the horizontal structure of convective heating differs from what is often assumed.