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arXiv · 1405.3071

On Large-Scale Dynamo Action at High Magnetic Reynolds Number

Fausto Cattaneo·Steven Tobias
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Abstract

We consider the generation of magnetic activity --- dynamo waves --- in the astrophysical limit of very large magnetic Reynolds number. We consider kinematic dynamo action for a system consisting of helical flow and large-scale shear. We demonstrate that large-scale dynamo waves persist at high $Rm$ if the helical flow is characterised by a narrow band of spatial scales and the shear is large enough. However for a wide band of scales the dynamo becomes small-scale with a further increase of $Rm$, with dynamo waves re-emerging only if the shear is then increased. We show that at high $Rm$ the key effect of the shear is to suppress small-scale dynamo action, allowing large-scale dynamo action to be observed. We conjecture that this supports a general "suppression principle" --- large-scale dynamo action can only be observed if there is a mechanism that suppresses the small-scale fluctuations.

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Fausto Cattaneo, Steven Tobias. 2014-05-13. On Large-Scale Dynamo Action at High Magnetic Reynolds Number. https://doi.org/10.1088/0004-637x/789/1/70

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