MAGNETIC BRAIDING AND PARALLEL ELECTRIC FIELDS
MAGNETIC BRAIDING AND PARALLEL ELECTRIC FIELDS
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DOI：
10.1088/0004-637x/696/2/1339
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发表时间：
2008-10
期刊：
影响因子：
--
通讯作者：
A. Wilmot-Smith;G. Hornig;D. Pontin
中科院分区：
文献类型：
--
作者：
A. Wilmot-Smith;G. Hornig;D. Pontin
太阳日冕磁场通过光球运动编织而成--伴随着随后的弛豫和磁场重联--是太阳物理学中最广泛争论的观点之一。我们根据三维磁重联理论的发展重新讨论了该理论。已知沿沿着场线的积分平行电场是决定重联速率的关键量，而在二维情况下电场本身是重要量。我们证明，这种差异变得至关重要的足够复杂的磁场结构。一个数值方法是用来放松编织磁场向一个理想的无力平衡，该领域被发现在整个放松保持平滑，只有大规模的电流结构。然而，在磁场中发现了具有极短长度尺度的高度非线性集成的平行电流结构，并且在弛豫过程中相关的梯度增强。一个分析模型的开发表明，在日冕的情况下，与集成的平行电流结构的长度尺度将迅速减少，随着复杂性的增加，或编织的程度，磁场。分析表明，对于任何有限的电阻率，这些长度尺度的减小最终将与日冕场的稳定性不一致。因此，磁编织过程的不可避免的后果是磁场的平衡的损失，可能通过磁重联事件。
The braiding of the solar coronal magnetic field via photospheric motions—with subsequent relaxation and magnetic reconnection—is one of the most widely debated ideas of solar physics. We readdress the theory in light of developments in three-dimensional magnetic reconnection theory. It is known that the integrated parallel electric field along field lines is the key quantity determining the rate of reconnection, in contrast with the two-dimensional case where the electric field itself is the important quantity. We demonstrate that this difference becomes crucial for sufficiently complex magnetic field structures. A numerical method is used to relax a braided magnetic field toward an ideal force-free equilibrium; the field is found to remain smooth throughout the relaxation, with only large-scale current structures. However, a highly filamentary integrated parallel current structure with extremely short length-scales is found in the field, with the associated gradients intensifying during the relaxation process. An analytical model is developed to show that, in a coronal situation, the length scales associated with the integrated parallel current structures will rapidly decrease with increasing complexity, or degree of braiding, of the magnetic field. Analysis shows the decrease in these length scales will, for any finite resistivity, eventually become inconsistent with the stability of the coronal field. Thus the inevitable consequence of the magnetic braiding process is a loss of equilibrium of the magnetic field, probably via magnetic reconnection events.