Model‐predicted distribution of wind‐induced internal wave energy in the world's oceans

Abstract

The distribution of wind‐induced internal wave energy in the world's oceans is investigated using a full three‐dimensional primitive equation model. Special attention is directed to the global energy input to the surface near‐inertial motions and the subsequent downward energy propagation into the deep ocean. We find that the model results for near‐inertial energy in the oceanic mixed layer, depth‐integrated horizontal energy fluxes, and vertical structures of WKB‐scaled kinetic energy are all consistent with the available observations in the regions of significant wind energy input and that the annual mean of the global wind energy input becomes ∼0.4 TW. It is also found that most of the wind‐induced energy resides in high vertical modes, 75–85% of which is dissipated in the surface 150 m. The present study therefore predicts that the total wind‐induced near‐inertial energy available for deep‐ocean mixing is limited to, at most, 0.1 TW, which is an order of magnitude smaller than previously estimated. Adding the energy flux from tide‐topography interactions of ∼0.9 TW, we can conclude that the total energy available for deep‐ocean mixing is ∼1.0 TW, obviously falling short of the required power to sustain the global overturning circulation. This might suggest the existence of other important energy sources, such as the one through geostrophic adjustment processes, and/or additional mechanisms sustaining the global overturning circulation, such as effects of Ekman upwelling in the Southern Ocean. Another possibility is that previous estimates of the volume transport of the global overturning circulation might be too large.