Effects of shell thickness on cross-helicity generation in convection-driven spherical dynamos

Silva, L. , Gupta, P., Mactaggart, D. and Simitev, R. (2020) Effects of shell thickness on cross-helicity generation in convection-driven spherical dynamos. Fluids, 5(4), 245. (doi: 10.3390/fluids5040245)

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The relative importance of the helicity and cross-helicity electromotive dynamo effects for self-sustained magnetic field generation by chaotic thermal convection in rotating spherical shells is investigated as a function of shell thickness. Two distinct branches of dynamo solutions are found to coexist in direct numerical simulations for shell aspect ratios between 0.25 and 0.6—a mean-field dipolar regime and a fluctuating dipolar regime. The properties characterising the coexisting dynamo attractors are compared and contrasted, including differences in temporal behaviour and spatial structures of both magnetic fields and rotating thermal convection. The helicity α-effect and the cross-helicity γ-effect are found to be comparable in intensity within the fluctuating dipolar dynamo regime, where their ratio does not vary significantly with the shell thickness. In contrast, within the mean-field dipolar dynamo regime the helicity α-effect dominates by approximately two orders of magnitude and becomes stronger with decreasing shell thickness.

Item Type:Articles
Additional Information:This research was funded by the Leverhulme Trust grant number RPG-2012-600. Numerical simulations were carried out in part at the DiRAC Data Centric system at Durham University, operated by the Institute for Computational Cosmology on behalf of the STFC DiRAC HPC Facility (www.dirac.ac.uk). This equipment was funded by BIS National E-infrastructure capital grant ST/K00042X/1, STFC capital grants ST/H008519/1 and ST/K00087X/1, STFC DiRAC Operations grant ST/K003267/1 and Durham University. DiRAC is part of the National E-Infrastructure.
Glasgow Author(s) Enlighten ID:Simitev, Professor Radostin and Gupta, Parag and Silva, Dr Luis and Mactaggart, Dr David
Creator Roles:
Silva, L.Validation, Investigation, Data curation, Visualization
Gupta, P.Investigation, Data curation, Visualization
Mactaggart, D.Formal analysis, Writing – review and editing
Simitev, R.Conceptualization, Methodology, Software, Formal analysis, Resources, Writing – original draft, Visualization, Supervision, Funding acquisition
Authors: Silva, L., Gupta, P., Mactaggart, D., and Simitev, R.
College/School:College of Science and Engineering
College of Science and Engineering > School of Mathematics and Statistics > Mathematics
Journal Name:Fluids
ISSN (Online):2311-5521
Copyright Holders:Copyright © 2020 by the authors
First Published:First published in Fluids 5(4):245
Publisher Policy:Reproduced under a Creative Commons license

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
166993Two-layer thermo-compositional dynamo models of the geomagnetic field.Radostin SimitevLeverhulme Trust (LEVERHUL)RPG-2012-600M&S - Mathematics