Generation of internal gravity waves by penetrative convection

TL;DR

This paper develops a semi-analytical model to estimate how penetrative convection generates internal gravity waves in stellar interiors, showing that it can be more efficient than turbulence and significantly influence angular momentum transport.

Contribution

The study introduces a novel semi-analytical approach to quantify wave generation by penetrative convection, highlighting its importance alongside turbulence in stellar angular momentum transport.

Findings

Penetrative convection generates more efficient internal gravity waves than turbulence in the solar case.

A smooth thermal transition enhances wave transmission into the radiative zone.

Plume-induced waves can significantly alter internal stellar rotation rates.

Abstract

The rich harvest of seismic observations over the past decade provides evidence of angular momentum redistribution in stellar interiors that is not reproduced by current evolution codes. In this context, transport by internal gravity waves can play a role and could explain discrepancies between theory and observations. The efficiency of the transport of angular momentum by waves depends on their driving mechanism. While excitation by turbulence throughout the convective zone has already been investigated, we know that penetrative convection into the stably stratified radiative zone can also generate internal gravity waves. Therefore, we aim at developing a semianalytical model to estimate the generation of IGW by penetrative plumes below an upper convective envelope. We derive the wave amplitude considering the pressure exerted by an ensemble of plumes on the interface between the radiative and convective zones as source term in the equation of momentum. We consider the effect of a thermal transition from a convective gradient to a radiative one on the transmission of the wave into the radiative zone. The plume-induced wave energy flux at the top of the radiative zone is computed for a solar model and is compared to the turbulence-induced one. We show that, for the solar case, penetrative convection generates waves more efficiently than turbulence and that plume-induced waves can modify the internal rotation rate on shorter time scales. We also show that a smooth thermal transition significatively enhances the wave transmission compared to the case of a steep transition. We conclude that driving by penetrative convection must be taken into account as much as turbulence-induced waves for the transport of internal angular momentum.