The TRR 181 seminar is held by Pablo Sebastia Saez (Universität Hamburg) on November 17 at Bundesstr. 53, 20146 Hamburg, room 22/23.

Interaction of Internal Gravity Waves with meso-scale eddies

Abstract

We investigate the interaction of internal gravity waves (IGW) with mesoscale eddies using the novel numerical Internal Wave Energy Model (IWEM). With IWEM, we evaluate the evolution, propagation and refraction of a typical internal wave spectrum  along a water column and over an eddy cross-section by the radiative transfer equation to investigate the energy exchange between internal waves and geostrophic (eddying) flows. We compare the simulations against observations of coherent mesoscale eddy features in the Canary Current System. Results show that the changes in wave energy are dominated by wave-eddy interaction and wave breaking at critical layers, while wave capture effects are two orders of magnitude smaller. Energy gain by wave-eddy interaction is dominated by low-frequency waves in the eddy center, while high-frequency waves are trapped in a cyclo-stationary up-/downward propagation cancelling out their gain or loss of energy. Energy loss by wave-eddy interaction or wave breaking is largest at the eddy rim, where waves undergo a downscale energy transfer to small vertical scales and to the inertial frequency. A shallow water maximum in stratification enhances the wave-eddy interaction and wave breaking. Following the Osborn-Cox relation, wave-breaking induced vertical diffusivities are found to be maximal at the eddy rim, partly in range with the observed values in the ocean. Internal wave-eddy interaction is therefore a plausible mechanism for explaining enhanced mixing at the near-surface.