MAGNETIC HELICITY FLUX IN THE PRESENCE OF SHEAR
2011 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 727, no 1, 11- p.Article in journal (Refereed) Published
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.
magnetohydrodynamics (MHD), Sun: dynamo, turbulence
Astronomy, Astrophysics and Cosmology
IdentifiersURN: urn:nbn:se:su:diva-67335DOI: 10.1088/0004-637X/727/1/11ISI: 000285992000011OAI: oai:DiVA.org:su-67335DiVA: diva2:470310
authorCount :22011-12-282011-12-282011-12-28Bibliographically approved