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arXiv 1607.00692astro-ph.SR
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日冕急流撕裂和间歇性的三维模拟

Three-Dimensional Simulations of Tearing and Intermittency in Coronal Jets

P. F. Wyper, C. R. DeVore, J. T. Karpen, B. J. Lynch

备注：
29 pages, 17 figures, accepted to ApJ
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摘要：

对日冕喷流的观测越来越多地表明，局部碎裂和不稳定性在这些事件的动力学中起着重要作用。在这项工作中，我们在闭场日冕中喷流的高分辨率模拟中研究了这种碎裂。我们研究了两种实现的嵌入双极模型，从而推动脉冲螺旋流出的扭曲和非扭曲的磁场之间的重联跨越圆顶扇平面的磁零。我们发现，重联区的碎片发生撕裂样的不稳定性，产生多个磁零点和磁通绳结构内的电流层。在电流层中心的弱场区域内形成的通量绳与密度增强的“斑点”相关联，当通量绳从层中射出时，这些斑点变成了附加的线，于是新的通量绳在它们后面形成。磁通绳的重复形成和喷射为在某些喷流中观察到的间歇性流出、明亮的发射斑点和无定形结构提供了自然的解释。这个过程的其他观测签名进行了讨论。基本上所有的喷流模型调用局部封闭和局部开放的领域作为喷流生成机制的区域之间的重连。因此，我们认为这种重复撕裂过程应该发生在所有射流中两个通量系统之间的分界面处。给出了三维撕裂射流重联的示意图。

英文摘要：

Observations of coronal jets increasingly suggest that local fragmentation and intermittency play an important role in the dynamics of these events. In this work we investigate this fragmentation in high-resolution simulations of jets in the closed-field corona. We study two realizations of the embedded-bipole model, whereby impulsive helical outflows are driven by reconnection between twisted and untwisted field across the domed fan plane of a magnetic null. We find that the reconnection region fragments following the onset of a tearing-like instability, producing multiple magnetic null points and flux-rope structures within the current layer. The flux ropes formed within the weak-field region in the center of the current layer are associated with "blobs" of density enhancement that become filamentary threads as the flux ropes are ejected from the layer, whereupon new flux ropes form behind them. This repeated formation and ejection of flux ropes provides a natural explanation for the intermittent outflows, bright blobs of emission, and filamentary structure observed in some jets. Additional observational signatures of this process are discussed. Essentially all jet models invoke reconnection between regions of locally closed and locally open field as the jet-generation mechanism. Therefore, we suggest that this repeated tearing process should occur at the separatrix surface between the two flux systems in all jets. A schematic picture of tearing-mediated jet reconnection in three dimensions is outlined.

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