Evolution and Fate of Wind-Derived Internal Wave Energy

When a wind stress is applied to the ocean surface, motions at the local inertial frequency are preferentially generated. Part of this energy is lost to near-surface dissipation, while the remain- der generates near-inertial waves that propagate vertically and horizontally into the stratified ocean. There, through a variety of nonlinear interaction processes between the near-inertial waves, geostrophic eddies, and the internal wave field, energy is eventually transferred to small scales at which wave breaking drives dissipation and small-scale mixing. However, there is substantial uncertainty about the global distribution of parameters that are key to accurately understanding the wind-driven portion of the ocean energetics, mainly: 1) the transmissivity, i.e., the proportion of wind-derived energy propagating into the interior rather than locally dis- sipated near the surface, and 2) the mixing efficiency, i.e., the fraction of energy lost in the interior to drive irreversible mixing compared to the total energy loss through mixing and dissipation. Both of these parameters are likely to vary depending on the environmental factors, and global ocean model results have been shown to be highly sensitive to them—yet they are often assumed to be constant because their distributions are poorly understood. Here, we propose an extensive high-resolution, process-based numerical study to determine the nonlinear interaction mechanisms responsible for setting the values of these two key parameters, and to estimate them on a global scale. The net result will be an important step in quantifying the role of wind-forced near-inertial oscillations in the ocean’s energy budget.