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Title:
The α effect in rotating convection with sinusoidal shear
Authors:
Käpylä, P. J.; Korpi, M. J.; Brandenburg, A.
Affiliation:
AA(Observatory, Tähtitorninmäki, PO Box 14, University of Helsinki, FI-00014 Helsinki, Finland; NORDITA, AlbaNova University Center, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden), AB(Observatory, Tähtitorninmäki, PO Box 14, University of Helsinki, FI-00014 Helsinki, Finland; NORDITA, AlbaNova University Center, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden), AC(NORDITA, AlbaNova University Center, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden; Department of Astronomy, AlbaNova University Center, Stockholm University, SE-10691 Stockholm, Sweden)
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 402, Issue 3, pp. 1458-1466. (MNRAS Homepage)
Publication Date:
03/2010
Origin:
WILEY
Astronomy Keywords:
convection, hydrodynamics, magnetic fields, MHD, turbulence
DOI:
10.1111/j.1365-2966.2009.16004.x
Bibliographic Code:
2010MNRAS.402.1458K

Abstract

Using three-dimensional convection simulations, it is shown that a sinusoidal variation of horizontal shear leads to a kinematic α 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 α 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 α effect.
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