Spontaneous generation of inertial waves from boundary turbulence in a librating sphere

TL;DR

This study demonstrates that inertial waves can spontaneously form in a librating sphere due to boundary turbulence, independent of libration frequency, with implications for planetary fluid dynamics.

Contribution

It reveals a new mechanism for inertial wave generation from boundary turbulence in rotating spheres, extending understanding beyond direct forcing scenarios.

Findings

Inertial waves are excited without direct forcing at certain frequencies.

Localized turbulence from centrifugal instabilities triggers wave generation.

The spectral analysis shows preferred excited frequencies.

Abstract

In this work, we report the excitation of inertial waves in a librating sphere even for libration frequencies where these waves are not directly forced. This spontaneous generation comes from the localized turbulence induced by the centrifugal instabilities in the Ekman boundary layer near the equator and does not depend on the libration frequency. We characterize the key features of these inertial waves in analogy with previous studies of the generation of internal waves in stratified flows from localized turbulent patterns. In particular, the temporal spectrum exhibits preferred values of excited frequency. This first-order phenomenon is generic to any rotating flow in the presence of localized turbulence and is fully relevant for planetary applications.