The impacts of ocean bottom roughness and tidal flow amplitude on abyssal mixing

Abstract

AbstractExisting parameterizations of vertical mixing over a rough ocean bottom neglect the transformation of linear internal waves into quasi‐steady internal lee waves, which occurs when tide‐topography interactions strengthen. In the present study, we perform a series of eikonal calculations to investigate the energy transfers from upward propagating quasi‐steady internal lee waves to dissipation scales through nonlinear interactions with the background Garrett‐Munk internal waves. For a fixed density stratification, the vertical group velocity of the quasi‐steady internal lee wave increases as either the horizontal wave number of the bottom topography or the tidal flow amplitude increases, whereas the life time of the quasi‐steady internal lee wave decreases as the horizontal wave number of the bottom topography increases but is relatively independent of the tidal flow amplitude. Consequently, the resulting bottom‐enhanced vertical mixing extends further upward as the tidal flow amplitude increases, nearly independent of the bottom roughness. We also find a tradeoff between the fraction of energy dissipated at the ocean bottom and the vertical extent of the energy dissipation region above the ocean bottom.