Stokes drift–induced and direct wind energy inputs into the Ekman layer within the Antarctic Circumpolar Current

Abstract

Theoretical analysis of energetics of the Ekman layer by incorporating the Coriolis‐Stokes forcing into the classical Ekman model shows that the wind energy input to the Ekman layer has two components: the work done by the wind stress on the surface Ekman current and that done by the Coriolis‐Stokes forcing on the whole body of water in the mixed layer. Under the assumption of constant vertical diffusivity, analytical forms of the direct wind energy input and the Stokes drift–induced energy input are derived. Assessments of relative importance of surface waves are made by comparing the wind energy input into the Ekman layer with and without wave‐induced Stokes drift effects included. Using the European Centre for Medium‐Range Weather Forecasts 40‐year reanalysis wind stress and surface wave data sets, the total rate of wind energy input into the Ekman layer within the Antarctic Circumpolar Current (ACC) is estimated to be 833 GW, in which the direct wind energy input is 650 GW (78%), and the Stokes drift–induced energy input is 183 GW (22%). The total mechanical energy input into the ACC due to wave effects is increased by approximately 4% (30 GW) compared to that into the classical Ekman layer. Long‐term variability of direct wind and Stokes drift–induced energy inputs to the ACC is also examined.