The role of lee waves for dissipation of transient eddies in the Southern Ocean

Mesoscale eddies play an important role in the Southern Ocean by transferring momentum, heat, and tracers horizontally and vertically. While the generation mechanisms for mesoscale eddies are well-understood, the processes governing their dissipation remain uncertain. Internal lee waves, generated by deep oceanic flows impinging on small-scale topography, have been suggested to sustain mixing in the deep Southern Ocean and apply drag on the time-mean flow of the Antarctic Circumpolar Current. In this study, we evaluate the role of lee waves for the equilibration of transient mesoscale eddies in the Southern Ocean using a 1/10° eddy-resolving model and linear lee wave theory. The results show that the energy dissipation of transient eddies due to lee wave generation is comparable to their dissipation due to turbulent bottom boundary layer (TBBL) drag and that lee waves make a stronger contribution to the equilibration of transient eddies than to the equilibration of the time-mean ACC. Our results imply that lee wave drag should be parameterised in eddy-resolving ocean models in order to improve their representation of eddies in the Southern Ocean and hence the response of the Southern Ocean to changes in winds.