Wind stress dependence on ocean surface velocity: Implications for mechanical energy input to ocean circulation

It is pointed out that accounting for an ocean surface velocity dependence in the wind stress tau can lead to a significant reduction in the rate at which winds input mechanical energy to the geostrophic circulation. Specifically, the wind stress is taken to be a quadratic function of a - u(o), where U-a and u(o) are the 10-m wind and ocean surface velocity, respectively. Because vertical bar U-a vertical bar is typically large relative to vertical bar u(o)vertical bar, accounting for a u(o) dependence leads only to relatively small changes in tau. The change to the basin-averaged wind power source, however, is considerably larger. Scaling arguments and quasigeostrophic simulations in a basin setting are presented. They suggest that the power source (or rate of energy input) is reduced by roughly 20%-35%.