The Elbert range of magnetostrophic convection. I. Linear theory

Susanne Horn, Jonathan M. Aurnou

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Abstract

In magnetostrophic rotating magnetoconvection, a fluid layer heated from below and cooled from above is equidominantly influenced by the Lorentz and the Coriolis forces. Strong rotation and magnetism each act separately to suppress thermal convective instability. However, when they act in concert and are near in strength, convective onset occurs at less extreme Rayleigh numbers ( , thermal forcing) in the form of a stationary, large-scale, inertia-less, inviscid magnetostrophic mode. Estimates suggest that planetary interiors are in magnetostrophic balance, fostering the idea that magnetostrophic flow optimizes dynamo generation. However, it is unclear if such a mono-modal theory is realistic in turbulent geophysical settings. Donna Elbert first discovered that there is a range of Ekman ( , rotation) and Chandrasekhar ( , magnetism) numbers, in which stationary large-scale magnetostrophic and small-scale geostrophic modes coexist. We extend her work by differentiating five regimes of linear stationary rotating magnetoconvection and by deriving asymptotic solutions for the critical wavenumbers and Rayleigh numbers. Coexistence is permitted if and . The most geophysically relevant regime, , is bounded by the Elsasser numbers . Laboratory and Earth's core predictions both exhibit stationary, oscillatory, and wall-attached multi-modality within the Elbert range. [Abstract copyright: © 2022 The Authors.]
Original languageEnglish
Article number20220313
Number of pages28
JournalPROC. R. SOC. - A.
Volume478
Issue number2264
Early online date10 Aug 2022
DOIs
Publication statusPublished - 31 Aug 2022

Bibliographical note

Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.

Funder


Funding Information: This research was supported by the National Science Foundation (J.M.A., EAR 1620649; EAR 1853196; EAR 2143939) and the Engineering and Physical Sciences Research Council (S.H., EP/V047388/1).

Keywords

  • Research articles
  • rotating convection
  • magnetoconvection
  • linear stability
  • dynamo

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