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The role of buoyancy in polarity reversals of the geodynamo

Sreenivasan, Binod and Sahoo, Swarandeep and Dhama, Gaurav (2014) The role of buoyancy in polarity reversals of the geodynamo. In: GEOPHYSICAL JOURNAL INTERNATIONAL, 199 (3). pp. 1698-1708.

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Official URL: http://dx.doi.org/ 10.1093/gji/ggu340


We investigate polarity reversals in the geodynamo using a rotating, convection-driven dynamo model. As the flow in rapidly rotating convection is dominated by columns aligned with the axis of rotation, the focus is on the dynamics of columnar vortices. By studying the growth of a seed magnetic field to a stable axial dipole field, we show that the magnetic field acts in ways that significantly enhance the relative helicity between cyclonic and anticyclonic vortices. This flow asymmetry is the hallmark of a dipolar dynamo. Strong buoyancy, on the other hand, offsets the effect of the magnetic field, establishing parity between positive and negative vortices. As the dipole field is deprived of the helicity required to support itself, the dynamo is pushed into a reversing state. This is a likely regime for polarity reversals in the Earth's core. The integral lengthscale at which buoyancy injects energy is not significantly different from the convective flow lengthscale, which implies that buoyancy does not feed vortices at the small scales where non-linear inertia is present. The lengthscale at which the Lorentz force acts in the reversing dynamo is small, which may allow the passive presence of non-linear inertia in the small scales.

Item Type: Journal Article
Additional Information: Copyright for this article belongs to the OXFORD UNIV PRESS, GREAT CLARENDON ST, OXFORD OX2 6DP, ENGLAND
Keywords: Numerical solutions; Dynamo: theories and simulations; Reversals: process, timescale, magnetostratigraphy; Planetary interiors
Department/Centre: Division of Mechanical Sciences > Centre for Earth Sciences
Date Deposited: 12 Jan 2015 04:54
Last Modified: 12 Jan 2015 04:54
URI: http://eprints.iisc.ac.in/id/eprint/50562

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