Ocean currents evident in satellite wind data

Satellite-mounted radar scatterometers designed to quantify surface winds o ver the ocean actually measure the relative motion between the air and the ocean surface. Estimates of the wind stress from conventional surface wind measurements are usually derived neglecting ocean currents. However, when t he relative motion is used, the differences in the estimated stress can be as large as 50% near the equator and may even reverse sign during an El Nin o. This assertion is supported by the strong relationship between the surfa ce currents measured by the Tropical Atmosphere-Ocean (TAO) array in the Pa cific Ocean and the differences between the winds estimated from scatterome ter data and those measured by TAO anemometers. The fact that the scatterom eter measures relative motion, and not wind alone, makes scatterometer-deri ved stress a more accurate representation of the boundary condition needed for both atmospheric and oceanic models than stress fields derived neglecti ng ocean currents.