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arXiv 1005.4669astro-ph.SR
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日冕物质抛射的起始:关于通量抵消模型的性质

Coronal mass ejection initiation: On the nature of the Flux Cancellation Model

Tahar Amari, Jean-Jacques Aly, Zoran Mikic, Jon A. Linker

摘要:

本文考虑了具有非零磁螺旋度的三维双极无力磁场,并研究了它在光球通量衰减驱动下的演化问题。对于这种特定的设置的通量抵消模型描述日冕物质抛射发生在活动区域,我们解决的问题的物理意义的通量减少,影响领域的演变的大小的域,这种减少是强加的,和存在的一个充满活力的标准,其特征在于可能发生的中断的配置。我们证明:(1)强迫通量消失可以解释为正、负通量向逆温线的输送,在那里它们被湮灭。(2)对于实际计算的特定情况下,其中的初始状态是相当剪切,形成一个扭曲的磁通绳和随后的全球中断的配置时,得到的通量已经减少了只有一个适度的量在整个活动区域的有限的一部分。(3)当磁能达到半开放场能量递减的量级,然后在达到相关的完全开放场能量之前,就会产生破坏。这表明导致破坏的机制是非平衡的,就像在整个区域强制通量减少的情况一样。

英文摘要:

We consider a three-dimensional bipolar force-free magnetic field with non zero magnetic helicity, occupying a half-space, and study the problem of its evolution driven by an imposed photospheric flux decrease. For this specific setting of the Flux Cancellation Model describing coronal mass ejections occuring in active regions, we address the issues of the physical meaning of flux decrease, of the influence on field evolution of the size of the domain over which this decrease is imposed, and of the existence of an energetic criterion characterizing the possible onset of disruption of the configuration. We show that: (1) The imposed flux disappearance can be interpreted in terms of transport of positive and negative fluxes towards the inversion line, where they get annihilated. (2) For the particular case actually computed, in which the initial state is quite sheared, the formation of a twisted flux rope and the subsequent global disruption of the configuration are obtained when the flux has decreased by only a modest amount over a limited part of the whole active region. (3) The disruption is produced when the magnetic energy becomes of the order of the decreasing energy of a semi-open field, and then before reaching the energy of the associated fully open field. This suggests that the mechanism leading to the disruption is nonequilibrium as in the case where flux is imposed to decrease over the whole region.

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