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

Lookup NU author(s): Dr Celine Guervilly

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This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0).


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 3-D. This approximation allows us to perform simulations for Ekman numbers down to 10−8, Prandtl numbers relevant for liquid metals (~10−1) and Reynolds numbers up to 3x104. 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 homogenized; 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.


Publication metadata

Author(s): Guervilly C, Cardin P

Publication type: Article

Publication status: Published

Journal: Geophysical Journal International

Year: 2017

Volume: 211

Issue: 1

Pages: 455-471

Print publication date: 01/10/2017

Online publication date: 28/07/2017

Acceptance date: 27/07/2017

Date deposited: 04/09/2017

ISSN (print): 0956-540X

ISSN (electronic): 1365-246X

Publisher: Oxford University Press

URL: https://doi.org/10.1093/gji/ggx315

DOI: 10.1093/gji/ggx315

Notes: pdf available on arxiv: https://arxiv.org/abs/1708.05342


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