Comment on egusphere-2022-294

Abstract

Wind work at the air-sea interface is the transfer of kinetic energy between the ocean and the atmosphere and, as such, is an important part of the atmosphere-ocean coupled system. Since wind work involves winds and ocean currents that span a broad range of spatial and temporal scales, a comprehensive study would require access to observations of a wide range of space and time scales. In the absence of appropriate global observations, our study makes use of a new, global, coupled ocean-atmosphere simulation with horizontal grid spacing of 2–5 km for the ocean and 7 km for the atmosphere. Here we develop a methodology, both in physical and spectral space, to diagnose different components of wind work in terms of forcing distinct classes of oceanic motions, including mean currents, time-dependent large-scale currents and mesoscale eddies, and internal gravity waves such as near-inertial waves. The total simulated wind work has a magnitude of 5.21 TW, a value much larger than reported by previous modeling studies. The total wind work is first decomposed into time-mean and time-dependent components, with the former accounting for 2.23 TW (43 %) and the latter 2.98 TW (57 %). The time-dependent wind work is then decomposed into two components, a high-frequency component that forces internal gravity waves and a low-frequency component that forces mesoscale eddies and large-scale currents. The high-frequency component is positive at scales between 10 km and 1000 km and represents 75 % of the total time-dependent component. The low-frequency component is found to be positive for spatial scales larger than 275 km and ten times larger than the negative part associated with smaller spatial scales. The negative wind work acts as a surface drag that slows down surface currents and damps mesoscale eddies whereas the positive low-frequency part accelerates large-scale currents. The complex and consequential interplay of surface winds and currents in the numerical simulation motivates the need for a winds-and-currents satellite mission to directly observe these wind work components.