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arXiv 1407.2272astro-ph.SR
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双层灯丝的缓慢上升和部分喷发。II。双通量绳平衡模型

Slow Rise and Partial Eruption of a Double-Decker Filament. II. Modeling by a Double Flux Rope Equilibrium

Bernhard Kliem, Tibor Török, Viacheslav S. Titov, Roberto Lionello, Jon A. Linker, Rui Liu, Chang Liu, Haimin Wang

摘要:

包含两个垂直排列的磁通量绳的手征和电流方向相同的无力平衡被认为是分裂丝/双折射和双折射-S型系统的模型。这样的平衡是通过Titov和Démoulin(1999)发展的方法的扩展在解析上构建的,并且通过包括光球边界中的剪切流、通量出现和通量抵消的演化序列在数值上构建的。它表明,分析平衡是稳定的,如果外部环形(剪切)场分量超过阈值。如果该分量充分地减小,则对于太阳活动区的典型条件,两个通量绳都变得不稳定,其中较低的绳通常首先不稳定。要么两条通量绳都向上喷发,要么只有上面的绳喷发,而下面的绳在日冕中与周围的通量重新连接并被破坏。然而,对于剪切场强度保持略高于阈值,配置也承认的演变,导致部分爆发,只有上部磁通绳变得不稳定,下部的一个留在原地。这可能是由磁通量和电流从下绳到上绳的转移触发的,正如论文I中对分裂灯丝的观察所表明的那样(Liu等人,2012年)。它也可能是由于在磁通绳之间的X型结构处与环境磁通的系绳切割重联,这同样以相反的方式影响它们的稳定性。这是证明了数字构造的平衡。

英文摘要:

Force-free equilibria containing two vertically arranged magnetic flux ropes of like chirality and current direction are considered as a model for split filaments/prominences and filament-sigmoid systems. Such equilibria are constructed analytically through an extension of the methods developed in Titov & Démoulin (1999) and numerically through an evolutionary sequence including shear flows, flux emergence, and flux cancellation in the photospheric boundary. It is demonstrated that the analytical equilibria are stable if an external toroidal (shear) field component exceeding a threshold value is included. If this component decreases sufficiently, then both flux ropes turn unstable for conditions typical of solar active regions, with the lower rope typically being unstable first. Either both flux ropes erupt upward, or only the upper rope erupts while the lower rope reconnects with the ambient flux low in the corona and is destroyed. However, for shear field strengths staying somewhat above the threshold value, the configuration also admits evolutions which lead to partial eruptions with only the upper flux rope becoming unstable and the lower one remaining in place. This can be triggered by a transfer of flux and current from the lower to the upper rope, as suggested by the observations of a split filament in Paper~I (Liu et al. 2012). It can also result from tether-cutting reconnection with the ambient flux at the X-type structure between the flux ropes, which similarly influences their stability properties in opposite ways. This is demonstrated for the numerically constructed equilibrium.

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