Influences of Random Surface Waves on the Estimates of Wind Energy Input to the Ekman Layer in the Antarctic Circumpolar Current Region

Sea surface waves significantly affect the wind energy input to the Ekman layer in the upper ocean. In the study, we first incorporated the wave-induced Coriolis-Stokes forcing, the reduction of wind stress caused by wave generation, and wave dissipation into the classical Ekman model to investigate the kinetic energy balance in the wave-affected Ekman layer. Then, both the theoretical steady state solution for the idealized condition and the nonsteady state solution for the realistic ocean were derived. Total energy input to the wave-affected Ekman layer includes the wind stress energy input and the wave-induced energy input. Based on the WAVEWATCH III model, the wave spectrum was simulated to represent realistic random directional wave conditions. The wind stress energy input and the wave-induced energy input to the wave-affected Ekman layer in the Antarctic Circumpolar Current in the period from 1988 to 2010 were then calculated. The annual mean total energy input in the Antarctic Circumpolar Current region was 402.5GW and the proportions of the wind stress energy input and the wave-induced energy input were, respectively, 85% and 15%. Particularly, total energy input in the Antarctic Circumpolar Current in the wave-affected Ekman layer model was 59.8% lower than that in the classical Ekman model. We conclude that surface waves play a significant role in the wind energy input to the Ekman layer. Plain Language Summary The wind energy input to the Ekman layer is one major source to balance the dissipation of mechanical energy in the ocean. Sea surface waves significantly influence the wind energy input to the Ekman layer. Previous studies only considered the Stokes drift induced by surface waves based on a simple monochromatic assumption. This study derived a realistic nonsteady state solution by incorporating three surface wave-related processes: wave-induced Coriolis-Stokes forcing, the reduction of wind stress caused by wave generation, and wave dissipation into the classical Ekman model. A numerical model was employed to simulate the wave spectra representing the realistic random surface waves. The total energy input in the Antarctic Circumpolar Current region from 1988 to 2010 was estimated. The estimated total energy input was 59.8% lower than that in the classical Ekman model, indicating that surface waves significantly affected the wind energy input in the Ekman layer.