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Axisymmetric field generation within an ambient axial field

Lookup NU author(s): Alhashmi Darah, Dr Graeme Sarson


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The generation of magnetic field in a homogeneous, electrically conducting fluid - as required for the dynamo generation of the fields of many astrophysical bodies - is normally a threshold process; the dynamo mechanism, applicable to such bodies in unmagnetised environments, requires motions of sufficient strength to overcome the innate magnetic diffusion. In the presence of an ambient field, however, the critical nature of the field generation process is relaxed. Motions can distort and amplify the ambient field for all amplitudes of flow. For motions with appropriate geometries, an internal 'dynamo-like' field of appreciable strength can be generated, even for relatively weak flows. At least a minority of planets, moons and other bodies exist within significant external astrophysical fields. For these bodies, the ambient field problem is more relevant than the classical dynamo problem, yet it remains relatively little studied. In this paper we consider the effect of an axial ambient field on a spherical mean-field α2ω dynamo model, through nonlinear calculations with α-quenching feedback. Ambient fields of varying strengths, and both stationary and oscillatory in time, are imposed. Particular focus is placed on the effects of these fields on the equatorial symmetry and the time dependence of the preferred solutions. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.

Publication metadata

Author(s): Darah AA, Sarson GR

Publication type: Article

Publication status: Published

Journal: Astronomische Nachrichten

Year: 2007

Volume: 328

Issue: 1

Pages: 25-35

ISSN (print): 0004-6337

ISSN (electronic): 1521-3994

Publisher: Wiley - VCH Verlag GmbH & Co. KGaA


DOI: 10.1002/asna.200610663


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