期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 402, 期 3, 页码 1458-1466出版社
WILEY-BLACKWELL
DOI: 10.1111/j.1365-2966.2009.16004.x
关键词
convection; hydrodynamics; magnetic fields; MHD; turbulence
资金
- Academy of Finland [121431, 112020]
- Swedish Research Council [621-2007-4064]
- European Research Council [227952]
- Academy of Finland (AKA) [112020] Funding Source: Academy of Finland (AKA)
Using three-dimensional convection simulations, it is shown that a sinusoidal variation of horizontal shear leads to a kinematic alpha 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 alpha 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 alpha effect.
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