Numerical Simulations of Three-dimensional Coronal Magnetic Fields Resulting from the Emergence of Twisted Magnetic Flux Tubes
Numerical Simulations of Three-dimensional Coronal Magnetic Fields Resulting from the Emergence of Twisted Magnetic Flux Tubes
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DOI：
10.1086/421238
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发表时间：
2004-07
期刊：
影响因子：
--
通讯作者：
Yuhong Fan;S. Gibson
中科院分区：
文献类型：
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作者：
Yuhong Fan;S. Gibson
我们给出了在低β区域的三维日冕磁场演化的MHD模拟结果，即一个拱形、扭曲的磁通管出现在一个预先存在的日冕势磁拱廊中。我们发现，当足够数量的扭转被输送到日冕中时，线系新兴通量管变得扭结不稳定。对于一个具有左旋扭曲的磁通管（这是北半球活跃区域磁通管的首选扭曲感），磁通管的扭结运动及其与周围日冕磁场的相互作用导致形成一个显示反s形状的强电流层，与北半球优先看到的x射线s型形态一致。电流层的位置与新兴磁通管的下边界磁场的关系也与观测到的x射线s形及其相关的光球双极磁区之间的空间关系很好地吻合。我们认为，形成的反s形电流层与受数值分辨率限制的磁切向不连续相一致，因此可能导致磁重联和显著的加热，导致x射线s形变亮。
We present the results of MHD simulations in the low-β regime of the evolution of the three-dimensional coronal magnetic field as an arched, twisted magnetic flux tube emerges into a preexisting coronal potential magnetic arcade. We find that the line-tied emerging flux tube becomes kink-unstable when a sufficient amount of twist is transported into the corona. For an emerging flux tube with a left-handed twist (which is the preferred sense of twist for active region flux tubes in the northern hemisphere), the kink motion of the tube and its interaction with the ambient coronal magnetic field lead to the formation of an intense current layer that displays an inverse-S shape, consistent with the X-ray sigmoid morphology preferentially seen in the northern hemisphere. The position of the current layer in relation to the lower boundary magnetic field of the emerging flux tube is also in good agreement with the observed spatial relations between the X-ray sigmoids and their associated photospheric bipolar magnetic regions. We argue that the inverse-S-shaped current layer formed is consistent with being a magnetic tangential discontinuity limited by numerical resolution and thus may result in the magnetic reconnection and significant heating that causes X-ray sigmoid brightenings.