The dynamics and excitation of torsional waves in geodynamo simulations

Teed, R. J. , Jones, C. A. and Tobias, S. M. (2014) The dynamics and excitation of torsional waves in geodynamo simulations. Geophysical Journal International, 196(2), pp. 724-735. (doi: 10.1093/gji/ggt432)

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The predominant force balance in rapidly rotating planetary cores is between Coriolis, pressure, buoyancy and Lorentz forces. This magnetostrophic balance leads to a Taylor state where the spatially averaged azimuthal Lorentz force is compelled to vanish on cylinders aligned with the rotation axis. Any deviation from this state leads to a torsional oscillation, signatures of which have been observed in the Earth's secular variation and are thought to influence length of day variations via angular momentum conservation. In order to investigate the dynamics of torsional oscillations (TOs), we perform several 3-D dynamo simulations in a spherical shell. We find TOs, identified by their propagation at the correct Alfvén speed, in many of our simulations. We find that the frequency, location and direction of propagation of the waves are influenced by the choice of parameters. Torsional waves are observed within the tangent cylinder and also have the ability to pass through it. Several of our simulations display waves with core traveltimes of 4–6 yr. We calculate the driving terms for these waves and find that both the Reynolds force and ageostrophic convection acting through the Lorentz force are important in driving TOs.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Teed, Dr Robert
Authors: Teed, R. J., Jones, C. A., and Tobias, S. M.
College/School:College of Science and Engineering > School of Mathematics and Statistics > Mathematics
Journal Name:Geophysical Journal International
Publisher:Oxford University Press
ISSN (Online):1365-246X
Published Online:16 November 2013
Copyright Holders:Copyright © 2013 The Authors
First Published:First published in Geophysical Journal International 196(2):724-435
Publisher Policy:Reproduced under a Creative Commons License

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