The TRR 181 seminar is held by Michael Cox (University of Edinburgh) on September 7, 11 am at Bundesstr. 53, 20146 Hamburg, room 22/23.

Inertia-gravity-wave diffusion by geostrophic turbulence: the role of time dependence and stratification change

Abstract

Inertia-gravity waves play a crucial role in ocean mixing. It has become increasingly clear that the distribution of IGW energy in spectral space is controlled by their interactions with the turbulent balanced flow. This interaction is a form of scattering which is approximately a diffusion process for action in wavevector space.

Previous work finds that in a three-dimensional system, action diffuses along constant-frequency cones, assuming (1) the flow is time-independent; and (2) the flow only affects the IGWs through Doppler shift. We relax these assumptions and account for (1) a slow time-dependent flow; and (2) the change in stratification the flow introduces. In the case of time-dependent flow, we find an explicit formula for the stationary wave-energy spectrum which is localised within a thin boundary layer around the constant-frequency cone. The spectrum performs well when compared to a high-resolution Boussinesq simulation. For the impact of stratification changes, we compare the case of a Boussinesq fluid with the shallow water system.