Regimes of thermo-compositional convection and related dynamos in rotating spherical shells

Mather, J. F. and Simitev, R. D. (2021) Regimes of thermo-compositional convection and related dynamos in rotating spherical shells. Geophysical and Astrophysical Fluid Dynamics, 115(1), pp. 61-84. (doi: 10.1080/03091929.2020.1762875)

Abstract

Convection and magnetic field generation in the Earth and planetary interiors are driven by both thermal and compositional gradients. In this work numerical simulations of finite-amplitude double-diffusive convection and dynamo action in rapidly rotating spherical shells full of incompressible two-component electrically-conducting fluid are reported. Four distinct regimes of rotating double-diffusive convection identified in a recent linear analysis (Silva, Mather and Simitev, Geophys. Astrophys. Fluid Dyn. 2019, 113, 377) are found to persist significantly beyond the onset of instability while their regime transitions remain abrupt. In the semi-convecting and the fingering regimes characteristic flow velocities are small compared to those in the thermally- and compositionally-dominated overturning regimes, while zonal flows remain weak in all regimes apart from the thermally-dominated one. Compositionally-dominated overturning convection exhibits significantly narrower azimuthal structures compared to all other regimes while differential rotation becomes the dominant flow component in the thermally-dominated case as driving is increased. Dynamo action occurs in all regimes apart from the regime of fingering convection. While dynamos persist in the semi-convective regime they are very much impaired by small flow intensities and very weak differential rotation in this regime which makes poloidal to toroidal field conversion problematic. The dynamos in the thermally-dominated regime include oscillating dipolar, quadrupolar and multipolar cases similar to the ones known from earlier parameter studies. Dynamos in the compositionally-dominated regime exhibit subdued temporal variation and remain predominantly dipolar due to weak zonal flow in this regime. These results significantly enhance our understanding of the primary drivers of planetary core flows and magnetic fields.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Simitev, Professor Radostin and Mather, Mr James
• Authors: Mather, J. F., and Simitev, R. D.
• College/School: College of Science and Engineering > School of Mathematics and Statistics; College of Science and Engineering > School of Mathematics and Statistics > Mathematics
• Journal Name: Geophysical and Astrophysical Fluid Dynamics
• Publisher: Taylor & Francis
• ISSN: 0309-1929
• ISSN (Online): 1029-0419
• Published Online: 14 May 2020
• Copyright Holders: Copyright © 2020 Informa UK Limited, trading as Taylor and Francis Group
• First Published: First published in Geophysical and Astrophysical Fluid Dynamics 115(1): 61-84
• Publisher Policy: Reproduced in accordance with the publisher copyright policy

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Project Code	Award No	Project Name	Principal Investigator	Funder's Name	Funder Ref	Lead Dept
166993		Two-layer thermo-compositional dynamo models of the geomagnetic field.	Radostin Simitev	Leverhulme Trust (LEVERHUL)	RPG-2012-600	M&S - Mathematics