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How magnetic helicity ejection helps large scale dynamos

Lookup NU author(s): Professor Axel Brandenburg, Dr Graeme Sarson


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There is mounting evidence that the ejection of magnetic helicity from the solar surface is important for the solar dynamo. Observations suggest that in the northern hemisphere the magnetic helicity flux is negative. We propose that this magnetic helicity flux is mostly due to small scale magnetic fields; in contrast to the more systematic large scale field of the 11 year cycle, whose helicity flux may be of opposite sign, and may be excluded from the observational interpretation. Using idealized simulations of MHD turbulence as well as a simple two-scale model, we show that shedding small scale (helical) field has two important effects. (i) The strength of the large scale field reaches the observed levels. (ii) The evolution of the large scale field proceeds on time scales shorter than the resistive time scale, as would otherwise be enforced by magnetic helicity conservation. In other words, the losses ensure that the solar dynamo is always in the near-kinematic regime. This requires, however, that the ratio of small scale to large scale losses cannot be too small, for otherwise the large scale field in the near-kinematic regime will not-reach the observed values. (C) 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.

Publication metadata

Author(s): Brandenburg A, Blackman EG, Sarson GR

Publication type: Conference Proceedings (inc. Abstract)

Publication status: Published

Conference Name: Magnetic Helicity at the Sun, In Solar Wind and Magnetospheres: Vistas from x-ray Observatories

Year of Conference: 2003

Pages: 1835-1844

ISSN: 0273-1177

Publisher: Pergamon


DOI: 10.1016/S0273-1177(03)00757-9

Library holdings: Search Newcastle University Library for this item

Series Title: Advances in Space Research