Damping mechanisms of internal waves in continuously stratified rotating basins

Abstract

Damping mechanisms, damping rates and the dissipative modal structure of internal waves in stratified rotating circular basins are investigated analytically. The damping is shown to be due to a combination of the internal-wave cancelling, where waves emitted by the oscillatory boundary layers destructively interact with the parent wave and drain energy from it, and spin-down modified by the periodicity, where the energy is drained by the sinks and sources at the bottom corner caused by a discontinuity in the Ekman transport. It is shown that super-inertial Poincaré waves and sub-inertial Kelvin waves are damped predominantly by the internal-wave cancelling and modified spin-down, respectively. These processes also modify the internal-wave structure; for super-inertial waves, the boundary-layer-generated waves intensify the interior flow in the lower part of the water column and delay the phase relative to the isopycnal displacements, but for sub-inertial waves, the Ekman pumping and the corner sinks and sources add a horizontal circular flow that slants the crest and trough backwards near the wall.