Direct evidence for an Ekman balance in the California Current

Abstract

Moored acoustic Doppler current profiler velocity estimates and buoy wind observations made during a period of moderate southward winds were used to test the Ekman balance at a site in the California Current. As in prior studies, the wind‐driven flow was separated from the total flow by subtraction of a deep reference current. The wind‐driven flow was shown to be in an Ekman balance on daily timescales over a period of several months. The mean observed transport was to the right of the wind and agreed to within 3% in magnitude and 4° in phase with the predicted Ekman transport, although the error bar was about 20%. The mean velocity profile was a smooth spiral, qualitatively similar (although flatter) than the theoretical Ekman spiral. Prom the observed mean momentum balance, profiles of the turbulent stress and eddy viscosity were inferred. Eddy viscosity estimates within the wind mixed layer were O (100 cm 2 s −1 ).