Impact of rotation on stochastic excitation of gravity and gravito-inertial waves in stars
1 Laboratoire AIM, CEA/DSM − CNRS − Université Paris Diderot, IRFU/SAp Centre de Saclay, 91191 Gif-sur-Yvette, France
2 LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Univ. Paris-Diderot, 5 place Jules Janssen, 92195 Meudon, France
Received: 4 May 2013
Accepted: 24 March 2014
Context. 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, a previous observational study of the CoRoT target HD 51452 demonstrated the potential strong impact of rotation on the stochastic excitation of gravito-inertial waves in stellar interiors.
Aims. Our goal is to explore and unravel the action of rotation on the stochastic excitation of gravity and gravito-inertial waves in stars.
Methods. The dynamics of gravito-inertial waves in stellar interiors in both radiation and in convection zones is described with a local non-traditional f-plane model. The coupling of these waves with convective turbulent flows, which leads to their stochastic excitation, is studied in this framework.
Results. First, we find that in the super-inertial regime in which the wave frequency is twice as high as the rotation frequency (σ > 2Ω), the evanescence of gravito-inertial waves in convective regions decreases with decreasing wave frequency. Next, in the sub-inertial regime (σ < 2Ω), 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 coupling 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. Finally, to study these mechanisms, the traditional approximation cannot be assumed because it does not properly treat the coupling between gravity and inertial waves in the sub-inertial regime.
Conclusions. Our results demonstrate the action of rotation on stochastic excitation of gravity waves thanks to the Coriolis acceleration, which modifies their dynamics in rapidly rotating stars and turbulent flows. As the ratio 2Ω/σ increases, the couplings and thus the amplitude of stochastic gravity waves are amplified.
Key words: hydrodynamics / waves / turbulence / stars: rotation / stars: evolution
© ESO, 2014