On Turbulence Losses at Rough Topography: LES results

With increasing slope steepness, conversion from the barotropic tide to internal waves increases in linear theory prediction. However, dissipative nonlinear features also become increasingly evident in observational studies and numerical simulations of wave generation at steep topography. High-resolution, three-dimensional LES have been performed to resolve turbulence, compute a closed baroclinic energy budget and quantify the local baroclinic energy loss, q. The tidal amplitude is varied for a model triangular ridge with different slope angles spanning sub- to supercritical topography. The LES results are used to extract the dependence of cycle-averaged q on the governing non-dimensional parameters as a step towards parameterization of internal tides in ocean models. Comparisons are made with observations and previous model studies at Luzon Strait and Kanea Ridge. The spatial distribution of cycle-averaged q, turbulent viscosity and turbulent diffusivity varies qualitatively among cases. Changes in q are linked to changes in the features responsible for turbulence which include one or more of the following: unstable wave shear, lee wave breaking, boundary layer shear, boundary layer inversions, downslope jets, and upslope bores.