在太阳速跃层中剪切驱动的磁浮力：由于旋转产生的平均电动势
Shear-driven magnetic buoyancy in the solar tachocline: The mean electromotive force due to rotation
摘要：
太阳磁周期的主要理论范例是一个$αω$ -发电机过程，其中差动旋转和湍流螺旋流的组合产生了每11年反转一次的大规模磁场。大多数$αω$太阳发电机模型依赖于太阳速跃层中的差异旋转来产生强的环向场。这样的模型中最有问题的部分是通过一个被称为$α$效应的过程产生大尺度极向场。虽然这通常归因于旋转影响下的小尺度对流运动，但这种再生过程的效率受到一些数值模拟的质疑。出于可能的条件内的速跃层，本文的目的是调查的极向场再生的替代机制，即在剪切产生的，旋转的磁性层的磁浮力不稳定性。我们使用一个局部的，完全可压缩的模型，其中施加的垂直剪切风了最初的垂直磁场。磁场最终变得非常不稳定，我们测量由此产生的平均电动势（EMF）。对于足够快的旋转，我们发现，平均电动势的一个重要组成部分是对齐的平均磁场的方向，这是典型的$αω$ -发电机模型的特征。因此，我们的研究结果表明，磁浮力可能直接有助于产生大规模的极向场在太阳。
英文摘要：
The leading theoretical paradigm for the Sun's magnetic cycle is an $αω$-dynamo process, in which a combination of differential rotation and turbulent, helical flows produces a large-scale magnetic field that reverses every 11 years. Most $αω$ solar dynamo models rely on differential rotation in the solar tachocline to generate a strong toroidal field. The most problematic part of such models is then the production of the large-scale poloidal field, via a process known as the $α$-effect. Whilst this is usually attributed to small-scale convective motions under the influence of rotation, the efficiency of this regenerative process has been called into question by some numerical simulations. Motivated by likely conditions within the tachocline, the aim of this paper is to investigate an alternative mechanism for the poloidal field regeneration, namely the magnetic buoyancy instability in a shear-generated, rotating magnetic layer. We use a local, fully compressible model in which an imposed vertical shear winds up an initially vertical magnetic field. The field ultimately becomes buoyantly unstable, and we measure the resulting mean electromotive force (EMF). For sufficiently rapid rotation, we find that a significant component of the mean EMF is aligned with the direction of the mean magnetic field, which is the characteristic feature of the classical $αω$-dynamo model. Our results therefore suggest that magnetic buoyancy could contribute directly to the generation of large-scale poloidal field in the Sun.
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