Inertial wave and zonal flow in librating spherical shells

TL;DR

This study numerically investigates inertial waves and zonal flows in librating spherical shells, confirming scaling laws and elucidating the boundary layer interactions that drive mean zonal flows relevant to planetary dynamics.

Contribution

It provides new numerical validation of shear layer scaling laws and clarifies the boundary layer mechanisms driving zonal flows in librating spherical shells.

Findings

Internal shear layers follow predicted scaling laws.

Mean zonal flows are driven by boundary layer nonlinearities.

Interior inertial wave interactions have minimal impact on zonal flows.

Abstract

We numerically study the inertial waves and zonal flows in spherical shells driven by longitudinal libration, an oscillatory variation of rotation rate. Internal shear layers are generated due to breakdown of the Ekman boundary layer at critical latitudes. Our numerical results validate the scaling laws of internal shear layers predicted by previous studies. Mean zonal flows are driven by the non-linear interaction in the boundary layers. Non-linear interaction of inertial waves in the interior fluids has no significant contribution to the zonal flow. Multiple geostrophic shear layers are generated due to non-linearities in the boundary layers at critical latitudes and reflection points of internal shear layers. We also investigate the scaling laws of geostrophic shear layers and extrapolate the results to the planetary setting.