Decadal variability of wind-energy input to the world ocean

Wind-stress energy input to the oceans is the most important source of mechanical energy in maintaining the oceanic general circulation. Previous studies indicate that wind-energy input to the Ekman layer and surface waves has varied greatly over the past 50 years. In this study, wind-energy input to surface current and surface geostrophic current was calculated as the scalar product of wind stress and surface current and surface geostrophic current. The surface geostrophic current was calculated in two ways: the surface geostrophic velocity was diagnosed from the TOPEX/POSEIDON altimeter data between 1993 and 2003, and calculated from the sea-surface height of the numerical model. The surface velocity was obtained from a numerical model. Estimate of wind-energy input based on altimetric data averaged over 1993–2003 is 0.84 TW (1TW=1012W), excluding the equatorial band (within ±3∘±3∘ of the equator). Estimate of the wind-energy input to the surface geostrophic current based on the numerical model is 0.87 TW averaged from 1993 to 2003, and wind-energy input to the surface current for the same period is 1.16 TW. This input is primarily concentrated over the Southern Ocean and the equatorial region (20∘S-20∘N)(20∘S-20∘N). This energy varied greatly on interannual and decadal time scales, and it increased 12% over the past 25 years, and the interannual variability mainly occurs in the latitude band of 40∘S-60∘S40∘S-60∘S and the equatorial region.