[AOS24-05] A new parameterization of tidal mixing enhanced over rough seafloor topography
Keywords:Parameterization, Energy dissipation rates , Vertical decay scale , Tidal flow , Rough abyssal seafloor , Internal lee waves
It is believed that tidal interaction with rough seafloor topography can create mixing hotspots extending off the seafloor. Although there exist fine-scale parameterizations of tidal mixing enhanced over rough seafloor, they do not reflect the fact that the internal waves emanating from rough seafloor transform from internal tidal waves to internal lee waves as tide-seafloor interaction strengthens with kHU0 /ω exceeding unity where kH is the dominant horizontal wavenumber of rough seafloor, U0 is the amplitude of tidal flow, and ω is tidal frequency. Taking into account this fact, we formulate here the vertical decay scale of energy dissipation rates over rough seafloor by multiplying the theoretically obtained vertical group velocities of internal lee waves by the time scale of their nonlinear interaction with the background Garrett-Munk internal wave field. The resulting formulation explicitly shows that the vertical extent of mixing hotspots over rough seafloor becomes independent of kH but proportional to U0 squared, which agrees very well with the results of eikonal experiments and consistent with the available data from the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES).