Large-scale dynamo action due to α alpha  fluctuations in a linear shear flow

Sridhar, S.; Singh, Nishant K.

Please use this identifier to cite or link to this item: http://hdl.handle.net/2289/6170

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DC Field	Value	Language
dc.contributor.author	Sridhar, S.	-
dc.contributor.author	Singh, Nishant K.	-
dc.date.accessioned	2015-02-12T06:25:31Z	-
dc.date.available	2015-02-12T06:25:31Z	-
dc.date.issued	2014-12-04	-
dc.identifier.citation	Monthly Notices of the Royal Astronomical Society, 2014, Vol. 445, p3770-3787	en
dc.identifier.issn	0035-8711	-
dc.identifier.issn	1365-2966 - (online)	-
dc.identifier.uri	http://hdl.handle.net/2289/6170	-
dc.description	Open Access	en
dc.description.abstract	We present a model of large-scale dynamo action in a shear flow that has stochastic, zero-mean fluctuations of the α parameter. This is based on a minimal extension of the Kraichnan–Moffatt model, to include a background linear shear and Galilean-invariant α-statistics. Using the first-order smoothing approximation we derive a linear integro-differential equation for the large-scale magnetic field, which is non-perturbative in the shearing rate S , and the α-correlation time τα . The white-noise case, τα = 0 , is solved exactly, and it is concluded that the necessary condition for dynamo action is identical to the Kraichnan–Moffatt model without shear; this is because white-noise does not allow for memory effects, whereas shear needs time to act. To explore memory effects we reduce the integro-differential equation to a partial differential equation, valid for slowly varying fields when τα is small but non-zero. Seeking exponential modal solutions, we solve the modal dispersion relation and obtain an explicit expression for the growth rate as a function of the six independent parameters of the problem. A non-zero τα gives rise to new physical scales, and dynamo action is completely different from the white-noise case; e.g. even weak α fluctuations can give rise to a dynamo. We argue that, at any wavenumber, both Moffatt drift and Shear always contribute to increasing the growth rate. Two examples are presented: (a) a Moffatt drift dynamo in the absence of shear and (b) a Shear dynamo in the absence of Moffatt drift.	en
dc.language.iso	en	en
dc.publisher	Oxford University Press for The Royal Astronomical Society	en
dc.relation.uri	http://adsabs.harvard.edu/abs/2014MNRAS.445.3770S	en
dc.relation.uri	http://arxiv.org/abs/1306.2495	en
dc.relation.uri	http://dx.doi.org/10.1093/mnras/stu1981	en
dc.rights	2014 The authors & the Royal Astronomical Society	en
dc.subject	MHD turbulence	en
dc.subject	magnetic fields	en
dc.title	Large-scale dynamo action due to α alpha fluctuations in a linear shear flow	en
dc.type	Article	en
Appears in Collections:	Research Papers (A&A)

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