Wyper P F, DeVore C R, Karpen J T, Lynch B J
Universities Space Research Association, NASA Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD 20771.
Heliophysics Science Division, NASA Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD 20771.
Astrophys J. 2016 Aug 10;827(1). doi: 10.3847/0004-637X/827/1/4. Epub 2016 Aug 3.
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.
对日冕喷流的观测越来越表明，局部碎片化和间歇性在这些事件的动力学中起着重要作用。在这项工作中，我们在封闭场日冕中喷流的高分辨率模拟中研究了这种碎片化。我们研究了嵌入双极模型的两种实现方式，即通过横跨磁零点圆顶扇形平面的扭曲场和未扭曲场之间的重连来驱动脉冲式螺旋外流。我们发现，重连区域在类似撕裂的不稳定性开始后会碎片化，在电流层内产生多个磁零点和通量绳结构。在电流层中心弱场区域形成的通量绳与密度增强的“团块”相关联，当通量绳从该层喷出时，这些团块会变成丝状线，随后在它们后面形成新的通量绳。通量绳的这种反复形成和喷出为在一些喷流中观测到的间歇性外流、明亮的发射团块和丝状结构提供了自然的解释。我们还讨论了这个过程的其他观测特征。基本上所有的喷流模型都将局部封闭场和局部开放场区域之间的重连作为喷流产生机制。因此，我们认为这种反复的撕裂过程应该发生在所有喷流中两个通量系统之间的分隔面上。本文概述了三维中撕裂介导的喷流重连的示意图。
