The [alpha] effect in rotating convection with sinusoidal shear

Using three-dimensional convection simulations, it is shown that a sinusoidal variation of horizontal shear leads to a kinematic a effect with a similar sinusoidal variation. The effect exists even for weak stratification and arises owing to the inhomogeneity of turbulence and the presence of impene...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society 2010-03, Vol.402 (3), p.1458-1466
Main Authors: Käpylä, P J, Korpi, M J, Brandenburg, A
Format: Article
Language:English
Subjects:
Astronomy
Fluid mechanics
Kinematics
Magnetic fields
Turbulent flow
Online Access:Get full text
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Summary:Using three-dimensional convection simulations, it is shown that a sinusoidal variation of horizontal shear leads to a kinematic a effect with a similar sinusoidal variation. The effect exists even for weak stratification and arises owing to the inhomogeneity of turbulence and the presence of impenetrable vertical boundaries. This system produces large-scale magnetic fields that also show a sinusoidal variation in the cross-stream direction. It is argued that earlier investigations overlooked these phenomena partly because of the use of horizontal averaging and also because measurements of a using an imposed field combined with long time averages give erroneous results. It is demonstrated that in such cases the actual horizontally averaged mean field becomes non-uniform. The turbulent magnetic diffusion term resulting from such non-uniform fields can then no longer be neglected and begins to balance the a effect.
ISSN:0035-8711
1365-2966
DOI:10.1111/j.1365-2966.2009.16004.x