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Scaling and intermittency in incoherent alpha-shear dynamo
Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
2012 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 420, no 3, 2170-2177 p.Article in journal (Refereed) Published
Abstract [en]

We consider mean-field dynamo models with fluctuating a effect, both with and without large-scale shear. The a effect is chosen to be Gaussian white noise with zero mean and a given covariance. In the presence of shear, we show analytically that (in infinitely large domains) the mean-squared magnetic field shows exponential growth. The growth rate of the fastest growing mode is proportional to the shear rate. This result agrees with earlier numerical results of Yousef et al. and the recent analytical treatment by Heinemann, McWilliams & Schekochihin who use a method different from ours. In the absence of shear, an incoherent a2 dynamo may also be possible. We further show by explicit calculation of the growth rate of third- and fourth-order moments of the magnetic field that the probability density function of the mean magnetic field generated by this dynamo is non-Gaussian.

Place, publisher, year, edition, pages
2012. Vol. 420, no 3, 2170-2177 p.
Keyword [en]
dynamo, magnetic fields, MHD, turbulence
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:su:diva-76959DOI: 10.1111/j.1365-2966.2011.20190.xISI: 000300702200024OAI: oai:DiVA.org:su-76959DiVA: diva2:535268
Note
2Available from: 2012-06-19 Created: 2012-05-28 Last updated: 2017-12-07Bibliographically approved

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Brandenburg, Axel
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Nordic Institute for Theoretical Physics (Nordita)Department of Astronomy
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