Morphological Classification of the Convective Regimes in Rotating Stars

Abstract

Abstract We present a set of numerical simulations that model the convection zones of solar-like stars. With this suite of numerical experiments, we explore how the nature of the convective structures transitions through a series of morphological regimes as the reduced Rayleigh number increases. Convection first manifests as a belt of rotationally aligned, convective, Taylor columns that circumscribes the equator. As the supercriticality increases, the poles begin to convect, initially in a cellular form, but eventually a plumy form emerges. Finally, at extremely high values of the Rayleigh number, a weakly rotating regime is achieved with antisolar differential rotation, i.e., the equator rotates more slowly than the poles. For all of these regimes, we provide theoretical and empirical scaling relations that summarize how global quantities—such as the bulk Rossby number and Reynolds number—scale with the Rayleigh and Ekman numbers. We demonstrate that a Rossby number based on the properties of the thermal boundary layer that clings to the outer surface of the convection zone works particularly well to predict the transition to antisolar differential rotation.