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arXiv 1111.6894astro-ph.SR
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来自笛卡尔对流模拟的振荡大尺度发电机

Oscillatory large-scale dynamos from Cartesian convection simulations

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

备注：
13 pages, 5 figures, version published in GAFD
发表信息：
Geophys. Astrophys. Fluid Dyn. 107, 244-257 (2013)
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摘要：

我们目前的结果，可压缩笛卡尔对流模拟和不施加剪切。在前一种情况下，发电机预计是$α^2\varOmega$类型，这通常预计与太阳有关，而后一种情况是指$α^2$发电机，这更有可能出现在更快速旋转的恒星，其差异旋转很小。我们进行了参数研究的剪切流和旋转的影响是不同的探测两种类型的发电机的相对重要性。当剪切速率与旋转速率的负比$q\equiv -S/\varOmega$在1.5和2之间时，即，当剪切和旋转强度相当时。振荡解的其他区域被发现具有小的$q$值，即，当剪切与旋转相比较弱时，以及当剪切与旋转相比非常强时，在大的负$q$ s范围内。然而，这些规则的例外情况也出现，使一个给定的比例的剪切旋转，解决方案是非振荡的小和大的剪切，但振荡的中间范围。将边界条件由垂直场改为理想导体场，发电机模式由振荡变为准稳态。此外，在许多情况下，振荡的解决方案只存在于运动制度，而在非线性阶段的平均场是平稳的。然而，有旋转和没有剪切的情况下，总是振荡的参数范围内研究和发电机模式不依赖于磁边界条件。然而，在饱和状态下的磁场的总的和大尺度分量的强度对所选择的边界条件敏感。

英文摘要：

We present results from compressible Cartesian convection simulations with and without imposed shear. In the former case the dynamo is expected to be of $α^2\varOmega$ type which is generally expected to be relevant for the Sun, whereas the latter case refers to $α^2$ dynamos which are more likely to occur in more rapidly rotating stars whose differential rotation is small. We perform a parameter study where the shear flow and the rotational influence are varied to probe the relative importance of both types of dynamos. Oscillatory solutions are preferred both in the kinematic and saturated regimes when the negative ratio of shear to rotation rates, $q\equiv -S/\varOmega$, is between 1.5 and 2, i.e., when shear and rotation are of comparable strengths. Other regions of oscillatory solutions are found with small values of $q$, i.e., when shear is weak in comparison to rotation, and in the regime of large negative $q$s, when shear is very strong in comparison to rotation. However, exceptions to these rules also appear so that for a given ratio of shear to rotation, solutions are non-oscillatory for small and large shear, but oscillatory in the intermediate range. Changing the boundary conditions from vertical field to perfect conductor ones changes the dynamo mode from oscillatory to quasi-steady. Furthermore, in many cases an oscillatory solution exists only in the kinematic regime whereas in the nonlinear stage the mean fields are stationary. However, the cases with rotation and no shear are always oscillatory in the parameter range studied here and the dynamo mode does not depend on the magnetic boundary conditions. The strengths of total and large-scale components of the magnetic field in the saturated state, however, are sensitive to the chosen boundary conditions.

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