Wave-Topography Interaction and Impact on Oceanic Kinetic Energy Distribution

This talk will explore the impact of ubiquitous variable ocean bathymetry with scales of 10-100 km on geostrophically balanced motions, e.g. Rossby waves and nonlinear mesoscale eddies. Variable bathymetry can alter the vertical structure and phase speed of Rossby waves and nonlinear eddies. The vertical structure of eddies in turn impacts the vertical structure of ocean eddy kinetic energy (EKE) and hence horizontal stirring. Therefore, understanding the impact of topography on the propagation (phase speed) and vertical structure of geostrophic motions is of global significance. These findings have important consequences for extrapolating surface observations to depth, as well as for the depth structure of eddy kinetic energy and turbulent energy cascades.

We present results based on analytical theory and nonlinear quasigeostrophic (QG) model results with realistic stratification. We find that rough ocean topography significantly alters the vertical structure and propagation speed of Rossby waves and eddies. Specifically, surface amplitudes are enhanced, deep velocities diminished, and propagation (phase) speed is increased by about a factor of 2. These analytical and model findings are consistent with the observed vertical structure from moored current meters. The QG model results help to justify a simplified theoretical calculation of the vertical structure of Rossby waves. Further, the QG model shows the impact of rough topography on turbulent energy cascades.