On the dynamics of overshooting convection in spherical shells: Effect of density stratification and rotation

TL;DR

This study uses 3D simulations to explore how density stratification and rotation influence overshooting convection in stellar shells, revealing complex dependencies and flow behaviors relevant to stellar interior dynamics.

Contribution

It systematically investigates the combined effects of density stratification and rotation on overshoot dynamics using global 3D simulations, a novel approach in this context.

Findings

Overshoot lengthscale depends on the ratio of density stratifications in the two zones.

Overshoot lengthscale decreases with decreasing Rossby number, scaling as Ro^{0.23}.

Mean flows extend beyond the convection zone into the stable region.

Abstract

Overshooting of turbulent motions from convective regions into adjacent stably stratified zones plays a significant role in stellar interior dynamics as this process may lead to mixing of chemical species, and contribute to the transport of angular momentum and magnetic fields. We present a series of fully non-linear, three-dimensional (3D) anelastic simulations of overshooting convection in a spherical shell which are focused on the dependence of the overshooting dynamics on the density stratification and the rotation, both key ingredients in stars which however have not been studied systematically together via global simulations. We demonstrate that the overshoot lengthscale is not simply a monotonic function of the density stratification in the convective region but instead, it depends on the ratio of the density stratifications in the two zones. Additionally, we find that the overshoot lengthscale decreases with decreasing Rossby number Ro and scales as Ro$^{0.23}$ while it also depends on latitude with higher Rossby cases leading to a weaker latitudinal variation. We examine the mean flows arising due to rotation and find that they extend beyond the base of the convection zone into the stable region. Our findings may provide a better understanding of the dynamical interaction between stellar convective and radiative regions, and motivate future studies particularly related to the solar tachocline and the implications of its overlapping with the overshoot region.