Inertial Wave Generation from Boundary Layer Turbulence
Abstract
Fluids inside rapidly rotating astrophysical objects are expected to obey the Taylor-Proudman theorem - the fluid velocity becomes aligned with the rotation axis. Any perturbation to this state gives rise to waves restored by the pressure gradient and Coriolis force, called inertial waves. These waves have frequencies less than twice the solid body rotation rate of the fluid. In addition, planetary bodies undergo modulation of their rotation rates in different ways, the most important of these being precession and libration. We explore the latter effect by simulating a spherical shell whose outer boundary undergoes libration - periodic changes in the rate of rotation. The inner boundary is kept fixed with a stress free boundary condition in order to minimise its role. We find that inertial waves with frequencies less than twice the mean outer boundary rotation rate are generated even though the forcing frequency may be higher. The reason is identified to be boundary layer turbulence near the equator of the outer boundary. These turbulent vortices provide the necessary perturbation for the generation of inertial waves. We successfully reproduce results observed by Sauret et. al. 2013 in the axisymmetric case and further explore the parameter space for non-axisymmetric instabilities.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMNG42A..05B
- Keywords:
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- 4415 Cascades;
- NONLINEAR GEOPHYSICS;
- 4568 Turbulence;
- diffusion;
- and mixing processes;
- OCEANOGRAPHY: PHYSICAL;
- 5405 Atmospheres;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS;
- 5430 Interiors;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS