Numerical investigation of the dependence of tidal mixing by wave--wave interactions on topographic and flow parameters

Abstract

Tidal flow over topography generates interior-ocean waves at the tidal frequency called internal tides. The breaking of these waves enhances the dissipation of turbulent kinetic energy and diapycnal mixing near and above the seafloor. More than half of the energy needed to maintain the ocean's global overturning circulation is supplied by the breaking of internal tides. Using non-hydrostatic simulations of the MIT general circulation model, we explore the effects of the following parameters on the fraction of the tidal energy dissipated locally above the topography and the vertical distribution of this dissipation: Coriolis frequency, topographic wavelength, ratio of the maximum topographic and wave slopes, stratification, and tidal amplitude. Unlike the monotonically decaying vertical profiles often used in coarse resolution general circulation models, our simulated dissipation deviates greatly from this simple model with enhanced dissipation from wave-wave interactions both near and far above the topography. The dissipation fraction is sensitive to variations in topographic and flow parameters, further demonstrating the need to progress from the constant 30% applied ubiquitously in global models.