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The influence of geometry and topology on axisymmetric mean-field dynamos

Lookup NU author(s): Professor Axel Brandenburg


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We study the changes in the dynamical behaviour of axisymmetric spherical mean-field dynamo models produced by changes in their geometry and topology, by considering a two parameter family of models, ranging from a full sphere to spherical shell, torus and disc-like configurations, within a unified framework. We find that the two parameter space of the family of models considered here separates into at least three different regions with distinct characteristics for the onset of dynamo action. In two of these regions, the most easily excited fields are oscillatory, in one case with dipolar symmetry, and in the other with quadrupolar, whereas in the third region the most easily excited field is steady and quadrupolar. In the nonlinear regime, we find that topological changes can alter significantly the dynamical behaviour, whilst modest changes in geometry can produce qualitative changes, particularly for thin disc-like configurations. This is of potential importance, since the exact shapes of astrophysical bodies, especially accretion discs and galaxies, are usually not precisely known.

Publication metadata

Author(s): Covas E, Tavakol R, Tworkowski A, Brandenburg A, Brooke J, Moss D

Publication type: Article

Publication status: Published

Journal: Astronomy and Astrophysics

Year: 1999

Volume: 345

Issue: 2

Pages: 669-679

Print publication date: 01/01/1999

ISSN (print): 0004-6361

ISSN (electronic): 1432-0746

Publisher: EDP Sciences