Impact of rotation on stochastic excitation of gravity and gravito-inertial waves in stars

Abstract

Gravity waves (or their signatures) are detected in stars thanks to helio- and asteroseismology and they may play an important role in the evolution of stellar angular momentum. Moreover, the observational study of the CoRoT target HD51452 by Neiner and collaborators demonstrated the potential strong impact of rotation on the stochastic excitation of gravito-inertial waves in stellar interiors. Our goal is to explore the action of rotation on the stochastic excitation of gravity and gravito-inertial waves in stars. The dynamics of gravito-inertial waves in stellar interiors, both in radiation and in convection zones, is described with a local non-traditional f-plane model. Their couplings with convective turbulent flows is studied in this framework. First, we find that, in the super-inertial regime in which the wave frequency is over twice the rotation frequency, the evanescence of gravito-inertial waves in convective regions decreases with decreasing wave frequency. Next, in the sub-inertial regime, gravito-inertial waves become purely propagative inertial waves in convection zones. Simultaneously, turbulence in convective regions is modified by rotation. Indeed, the turbulent energy cascade towards small scales is slowed down and in the case of rapid rotation, strongly anisotropic turbulent flows are obtained that can be understood as complex non-linear triadic interactions of propagative inertial waves. These different behaviours, due to the action of the Coriolis acceleration, strongly modify the wave couplings with turbulent flows. On one hand, turbulence weakly influenced by rotation is coupled with evanescent gravito-inertial waves. On the other hand, rapidly rotating turbulence is intrinsically and strongly coupled with sub-inertial waves.