Diffusion-free scaling in rotating spherical Rayleigh-B\'enard convection

TL;DR

This study uses direct numerical simulations to identify three distinct flow regions in rotating spherical Rayleigh-Bénard convection, revealing that bulk-dominated diffusion-free scaling occurs specifically in the mid-latitude region, highlighting differences from planar convection.

Contribution

The paper demonstrates the existence of three distinct flow regions in spherical convection and identifies the mid-latitude region as the source of diffusion-free scaling, a novel insight into spherical convection physics.

Findings

Three flow regions identified: low-latitude, mid-latitude, equator.

Diffusion-free scaling originates from the mid-latitude region.

Flow physics differ significantly from planar convection.

Abstract

Direct numerical simulations are employed to reveal three distinctly different flow regions in rotating spherical Rayleigh-B\'enard convection. In the low-latitude region $\mathrm{I}$ vertical (parallel to the axis of rotation) convective columns are generated between the hot inner and the cold outer sphere. The mid-latitude region $\mathrm{II}$ is dominated by vertically aligned convective columns formed between the Northern and Southern hemispheres of the outer sphere. The diffusion-free scaling, which indicates bulk-dominated convection, originates from this mid-latitude region. In the equator region $\mathrm{III}$ the vortices are affected by the outer spherical boundary and are much shorter than in region $\mathrm{II}$. Thermally driven turbulence with background rotation in spherical Rayleigh-B\'enard convection is found to be characterized by three distinctly different flow regions. The diffusion-free scaling, which indicates the heat transfer is bulk-dominated, originates from the mid-latitude region in which vertically aligned vortices are stretched between the Northern and Southern hemispheres of the outer sphere.\ These results show that the flow physics in rotating convection are qualitatively different in planar and spherical geometries. This finding underlines that it is crucial to study convection in spherical geometries to better understand geophysical and astrophysical flow phenomena.