大尺度扭曲的磁结构如何从浮力不稳定性中自然产生？
How can large-scale twisted magnetic structures naturally emerge from buoyancy instabilities?
摘要：
本文研究了多变大气中水平磁场层的三维不稳定性，与以前的研究相反，在这种大气中，初始状态的磁力线不是单向的。我们表明，如果扭转最初集中在不稳定层内，那么几位作者（例如，见Cattaneo等人（1990））所报道的不稳定性的改变，只有在计算限于二维时才能观察到。在三维中，通常的交换不稳定性发生在层和无场区域之间的界面处的场线所固定的方向上。因此，我们引入了一种新的配置：不稳定性现在在弱磁化的大气中发展，磁场的方向可以相对于下面的强不稳定场的方向而变化，扭曲现在集中在上界面。线性稳定性分析和非线性直接数值模拟被用来研究这种配置。我们发现，从小尺度的交换不稳定性，大尺度的扭曲相干磁结构自发形成，与可能的影响，形成活动区从一个深层次的太阳磁场。
英文摘要：
We consider the three-dimensional instability of a layer of horizontal magnetic field in a polytropic atmosphere where, contrary to previous studies, the field lines in the initial state are not unidirectional. We show that if the twist is initially concentrated inside the unstable layer, the modifications of the instability reported by several authors (see e.g. Cattaneo et al. (1990)) are only observed when the calculation is restricted to two dimensions. In three dimensions, the usual interchange instability occurs, in the direction fixed by the field lines at the interface between the layer and the field-free region. We therefore introduce a new configuration: the instability now develops in a weakly magnetised atmosphere where the direction of the field can vary with respect to the direction of the strong unstable field below, the twist being now concentrated at the upper interface. Both linear stability analysis and non-linear direct numerical simulations are used to study this configuration. We show that from the small-scale interchange instability, large-scale twisted coherent magnetic structures are spontaneously formed, with possible implications to the formation of active regions from a deep-seated solar magnetic field.
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