Internal gravity wave and tide interaction with geostrophic mean flow

Abstract

Internal gravity waves (IGW) are ubiquitous in the open and coastal ocean. IGWs are refracted by their changing environment and may gain energy from or loose energy to the geostrophically balanced mean flow with vertical (wave drag) or horizontal shear (wave capture). Refraction, wave-wave interaction, or scattering at mean flow, topography, or turbulence can generate wave energy fluxes towards smaller wavelengths, where IGW break and mix density, which can drive in turn large scale mean flow. Two case studies of interaction of waves and mean-flow and their consequences for mixing are presented: Using a novel numerical model (IWEM) of the spectral energy balance of IGWs, we simulate the interaction of IGWs with an observed coherent meso-scale eddy in the coastal upwelling region off Mauretania. Using ray traycing we study the interaction of low mode IGWs at tidal frequencies (internal tides) with a geostrophic mean flow given by a realistic meso-scale eddy field.