On the Modulation of Kinetic Energy Transfer by Internal Tides.

The question of how kinetic energy (KE) is dissipated in the ocean remains a key question in physical oceanography. Recent literature suggests that quasi-balanced submesoscale motions and internal gravity waves (IGWs) can play an active role in fluxing kinetic energy towards dissipative scales. The process and mechanisms by which these classes of motions may provide a route to dissipation remain as open questions. In this study, we investigate the impact of internal tides generated by tidal motions on cross-scale kinetic energy exchanges at midlatitude. Our analysis is based on the output of two NEMO based sub-mesoscale permitting ocean model simulations of the North Atlantic ocean (with/without tidal forcing). Our results show that resolving both submesoscales and IGWs yields a strong forward cascade toward dissipative scales. But we find that different mechanisms are controlling this forward cascade depending on the season. In wintertime, energetic submesoscales are the key driver for the forward cascade of KE while in summertime IGWs are responsible for the forward cascade. We found that, in both seasons, the forward cascade at high wavenumbers extends vertically over a significant fraction of the upper ocean.