Multiple zonal jets and convective heat transport barriers in a quasi-geostrophic model of planetary cores

TL;DR

This study uses a quasi-geostrophic model to explore how multiple zonal jets influence convective heat transport in rapidly rotating planetary cores, revealing that jet structure significantly impacts heat transfer efficiency.

Contribution

It introduces a novel quasi-geostrophic simulation approach for planetary core convection, highlighting the role of zonal jets in modulating heat transport.

Findings

Retrograde jets create steep temperature gradients and conduction-dominated heat transfer.

Prograde jets facilitate efficient convective heat transport and homogenize temperature.

Jet width controls the overall heat transfer efficiency in the system.

Abstract

We study rapidly-rotating Boussinesq convection driven by internal heating in a full sphere. We use a numerical model based on the quasi-geostrophic approximation for the velocity field, whereas the temperature field is three-dimensional. This approximation allows us to perform simulations for Ekman numbers down to 1e-8, Prandtl numbers relevant for liquid metals (~0.1) and Reynolds numbers up to 3e4. Persistent zonal flows composed of multiple jets form as a result of the mixing of potential vorticity. For the largest Rayleigh numbers computed, the zonal velocity is larger than the convective velocity despite the presence of boundary friction. The convective structures and the zonal jets widen when the thermal forcing increases. Prograde and retrograde zonal jets are dynamically different: in the prograde jets (which correspond to weak potential vorticity gradients) the convection transports heat efficiently and the mean temperature tends to be homogenised; by contrast, in the cores of the retrograde jets (which correspond to steep gradients of potential vorticity) the dynamics is dominated by the propagation of Rossby waves, resulting in the formation of steep mean temperature gradients and the dominance of conduction in the heat transfer process. Consequently, in quasi-geostrophic systems, the width of the retrograde zonal jets controls the efficiency of the heat transfer.