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Boundary effects and propagating, magnetic fronts in disc dynamos

Lookup NU author(s): Professor Anvar Shukurov, Professor Dmitry Sokoloff

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Abstract

We discuss the validity and accuracy of thin-disc asymptotic solutions of the mean-field dynamo equations, using a new numerical code to perform calculations for embedded disc models, with high spatial resolution on a nonuniform grid. We show that there is reasonable agreement between conventional linear asymptotic solutions (using vacuum boundary conditions) and numerical results, provided that the concept of effective disc thickness is introduced. This result is of more general significance in the context of disc dynamo models, in that it is necessary to redefine the dynamo number of models with vacuum boundary conditions in order to apply them to realistic discs without sharp boundaries. We also consider the effects of competition between eigenmodes with different growth rates localized in different regions of the disc. A front associated with the faster growing eigenmode propagates through the disc and eventually dominates the solution. Under typical galactic conditions, the frontal velocity is typically a few kms-1. The propagation of fronts outwards from central regions can provide seed fields for subsequent mean field dynamo action that are stronger than conventionally assumed.


Publication metadata

Author(s): Moss D, Shukurov A, Sokoloff D

Publication type: Article

Publication status: Published

Journal: Geophysical and Astrophysical Fluid Dynamics

Year: 1998

Volume: 89

Issue: 3-4

Pages: 285-308

Print publication date: 01/01/1998

ISSN (print): 0309-1929

ISSN (electronic): 1026-7506

Publisher: Taylor & Francis

URL: http://dx.doi.org/10.1080/03091929808203688

DOI: 10.1080/03091929808203688


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