The classical formulation for Ekman pumping that relates upwelling velocity to the curl of the wind stress neglects the effects of surface currents and air-sea interaction. Presently available satellite data are limited to investigation of these effects on scales larger than about 100 km. The data reveal that the curl of the wind stress is essentially negligible compared with Ekman pumping from the effects of surface currents and air-sea interaction on these resolvable scales.
Numerical simulations with high spatial resolution find that the Ekman pumping velocities from surface currents and air-sea interaction increase dramatically with decreasing scales, with the former exceeding 50 m/day on scales shorter than about 10 km. Two future satellite missions offer promising prospects for estimates of the surface current induced Ekman pumping on scales smaller than 100 km. One of these is the Surface Water/Ocean Topography (SWOT) altimetric mission with a planned launch in 2020. The other, which is in the early planning stages, is a scatterometer mission to measure surface winds and surface ocean velocity, tentatively called the Winds and Currents Mission (WaCM).
The scale dependencies of surface current effects on Ekman pumping, and the limitations of SWOT and WaCM measurement errors, will be assessed from a high-resolution numerical model of the California Current System. It will be shown that both of the future satellite missions can provide valuable observations on scales much shorter than can be resolved from presently available satellite data.