Sensitivity to luminosity, centrifugal force, and boundary conditions in spherical shell convection

TL;DR

This study investigates how variations in luminosity, boundary conditions, and centrifugal force influence spherical shell convection simulations, finding that some parameters have minor effects while others significantly impact convection dynamics.

Contribution

The paper systematically assesses the sensitivity of spherical shell convection models to key physical parameters, demonstrating the robustness of the fully compressible approach with the Pencil Code.

Findings

Luminosity variations have minor effects on large-scale dynamics.

Centrifugal force influences solutions only at unrealistically high magnitudes.

Photospheric physics parameterization affects convection anisotropy and deviation from Taylor-Proudman state.

Abstract

We test the sensitivity of hydrodynamic and magnetohydrodynamic turbulent convection simulations with respect to Mach number, thermal and magnetic boundary conditions, and the centrifugal force. We find that varying the luminosity, which also controls the Mach number, has only a minor effect on the large-scale dynamics. A similar conclusion can also be drawn from the comparison of two formulations of the lower magnetic boundary condition with either vanishing electric field or current density. The centrifugal force has an effect on the solutions, but only if its magnitude with respect to acceleration due to gravity is by two orders of magnitude greater than in the Sun. Finally, we find that the parameterisation of the photospheric physics, either by an explicit cooling term or enhanced radiative diffusion, is more important than the thermal boundary condition. In particular, runs with cooling tend to lead to more anisotropic convection and stronger deviations from the Taylor-Proudman state. In summary, the fully compressible approach taken here with the Pencil Code is found to be valid, while still allowing the disparate timescales to be taken into account.