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arXiv 0908.2423astro-ph.SR
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具有正弦剪切的旋转对流中的α效应

The alpha effect in rotating convection with sinusoidal shear

P. J. Käpylä, M. J. Korpi, A. Brandenburg

备注：
9 pages, 10 figures, published version
发表信息：
Monthly Notices Roy. Astron. Soc. 402, 1458-1466 (2010)
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摘要：

利用三维对流模拟表明，水平剪切的正弦变化导致具有类似正弦变化的运动学α效应。这种效应甚至在弱层结的情况下也存在，并且由于湍流的不均匀性和难以穿透的垂直边界的存在而产生。该系统产生的大尺度磁场也显示出在流向方向上的正弦变化。有人认为，早期的研究忽略了这些现象，部分原因是使用水平平均，也因为测量α使用一个强加的字段结合长时间的平均给出错误的结果。它表明，在这种情况下，实际的水平平均场变得不均匀。由这种非均匀场引起的湍流磁扩散项不再可以忽略，并开始平衡α效应。

英文摘要：

Using three-dimensional convection simulations it is shown that a sinusoidal variation of horizontal shear leads to a kinematic αeffect 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 streamwise direction. It is argued that earlier investigations overlooked these phenomena partly because of the use of horizontal averaging and also because measurements of αusing 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 αeffect.

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