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Scale separated low viscosity dynamos and dissipation within the Earth’s core

The mechanism by which the Earth’s magnetic field is generated is thought to be thermal convection in the metallic liquid iron core. Here we present results of a suite of self-consistent spherical shell computations with ultra-low viscosities that replicate this mechanism, but using diffusivities of...

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Autores principales: Sheyko, Andrey, Finlay, Christopher, Favre, Jean, Jackson, Andrew
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Nature Publishing Group UK 2018
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6105638/
https://www.ncbi.nlm.nih.gov/pubmed/30135480
http://dx.doi.org/10.1038/s41598-018-30864-1
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author Sheyko, Andrey
Finlay, Christopher
Favre, Jean
Jackson, Andrew
author_facet Sheyko, Andrey
Finlay, Christopher
Favre, Jean
Jackson, Andrew
author_sort Sheyko, Andrey
collection PubMed
description The mechanism by which the Earth’s magnetic field is generated is thought to be thermal convection in the metallic liquid iron core. Here we present results of a suite of self-consistent spherical shell computations with ultra-low viscosities that replicate this mechanism, but using diffusivities of momentum and magnetic field that are notably dissimilar from one another. This leads to significant scale separation between magnetic and velocity fields, the latter being dominated by small scales. We show a zeroth order balance between the azimuthally-averaged parts of the Coriolis and Lorentz forces at large scales, which occurs when the diffusivities of magnetic field and momentum differ so much, as in our model. Outside boundary layers, viscous forces have a magnitude that is about one thousandth of the Lorentz force. In this dynamo dissipation is almost exclusively Ohmic, as in the Earth, with convection inside the so-called tangent cylinder playing a crucial role; it is also in the “strong field” regime, with significantly more magnetic energy than kinetic energy (as in the Earth). We finally show a robust empirical scaling law between magnetic dissipation and magnetic energy.
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spelling pubmed-61056382018-08-27 Scale separated low viscosity dynamos and dissipation within the Earth’s core Sheyko, Andrey Finlay, Christopher Favre, Jean Jackson, Andrew Sci Rep Article The mechanism by which the Earth’s magnetic field is generated is thought to be thermal convection in the metallic liquid iron core. Here we present results of a suite of self-consistent spherical shell computations with ultra-low viscosities that replicate this mechanism, but using diffusivities of momentum and magnetic field that are notably dissimilar from one another. This leads to significant scale separation between magnetic and velocity fields, the latter being dominated by small scales. We show a zeroth order balance between the azimuthally-averaged parts of the Coriolis and Lorentz forces at large scales, which occurs when the diffusivities of magnetic field and momentum differ so much, as in our model. Outside boundary layers, viscous forces have a magnitude that is about one thousandth of the Lorentz force. In this dynamo dissipation is almost exclusively Ohmic, as in the Earth, with convection inside the so-called tangent cylinder playing a crucial role; it is also in the “strong field” regime, with significantly more magnetic energy than kinetic energy (as in the Earth). We finally show a robust empirical scaling law between magnetic dissipation and magnetic energy. Nature Publishing Group UK 2018-08-22 /pmc/articles/PMC6105638/ /pubmed/30135480 http://dx.doi.org/10.1038/s41598-018-30864-1 Text en © The Author(s) 2018 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.
spellingShingle Article
Sheyko, Andrey
Finlay, Christopher
Favre, Jean
Jackson, Andrew
Scale separated low viscosity dynamos and dissipation within the Earth’s core
title Scale separated low viscosity dynamos and dissipation within the Earth’s core
title_full Scale separated low viscosity dynamos and dissipation within the Earth’s core
title_fullStr Scale separated low viscosity dynamos and dissipation within the Earth’s core
title_full_unstemmed Scale separated low viscosity dynamos and dissipation within the Earth’s core
title_short Scale separated low viscosity dynamos and dissipation within the Earth’s core
title_sort scale separated low viscosity dynamos and dissipation within the earth’s core
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6105638/
https://www.ncbi.nlm.nih.gov/pubmed/30135480
http://dx.doi.org/10.1038/s41598-018-30864-1
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