An update on the wind power input to the surface geostrophic flow of the World Ocean

The rate of working of the surface wind stress on the geostrophic component of the surface flow of the World Ocean is revisited. The global mean is found to be about 0.85 to 1.0 TW. Consistent with previous estimates, about 0.75 to 0.9 TW comes from outside the equatorial region (poleward of 3). The rate of forcing of fluctuating currents integrates to only about 0.02 TW when the equatorial region is included, or close to zero over the extratropical region. Uncertainty in wind power input due to uncertainty in the surface currents is negligible. Results from several different wind stress products are compared, suggesting that uncertainty in wind stress is the dominant source of error. Ignoring the surface currents’ influence upon wind stress leads to a systematic bias in net wind power input; an overestimate of about 10 to 30%. (In previous estimates this positive bias was offset by too weak winds.) Small-scale, zonally elongated structures in the wind power input were found, but have both positive and negative contributions and lead to little net wind power input.