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MAGNETIC HELICITY FLUX IN THE PRESENCE OF SHEAR
Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Stockholm University, Faculty of Science, Department of Astronomy.
2011 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 727, no 1, 11- p.Article in journal (Refereed) Published
Abstract [en]

Magnetic helicity has risen to be a major player in dynamo theory, with the helicity of the small-scale field being linked to the dynamo saturation process for the large-scale field. It is a nearly conserved quantity, which allows its evolution equation to be written in terms of production and flux terms. The flux term can be decomposed in a variety of fashions. One particular contribution that has been expected to play a significant role in dynamos in the presence of mean shear was isolated by Vishniac & Cho. Magnetic helicity fluxes are explicitly gauge dependent however, and the correlations that have come to be called the Vishniac-Cho flux were determined in the Coulomb gauge, which turns out to be fraught with complications in shearing systems. While the fluxes of small-scale helicity are explicitly gauge dependent, their divergences can be gauge independent. We use this property to investigate magnetic helicity fluxes of the small-scale field through direct numerical simulations in a shearing-box system and find that in a numerically usable gauge the divergence of the small-scale helicity flux vanishes, while the divergence of the Vishniac-Cho flux remains finite. We attribute this seeming contradiction to the existence of horizontal fluxes of small-scale magnetic helicity with finite divergences.

Place, publisher, year, edition, pages
2011. Vol. 727, no 1, 11- p.
Keyword [en]
magnetohydrodynamics (MHD), Sun: dynamo, turbulence
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:su:diva-67335DOI: 10.1088/0004-637X/727/1/11ISI: 000285992000011OAI: oai:DiVA.org:su-67335DiVA: diva2:470310
Note
authorCount :2Available from: 2011-12-28 Created: 2011-12-28 Last updated: 2017-12-08Bibliographically approved

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Nordic Institute for Theoretical Physics (Nordita)Department of Astronomy
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