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arXiv 0902.3705astro-ph.SR
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CME后电流片的形态和密度

Morphology and density of post-CME current sheets

B. Vršnak, G. Poletto, E. Vujić, A. Vourlidas, Y. -K. Ko, J. C. Raymond, A. Ciaravella, T. Žic, D. F. Webb, A. Bemporad, F. Landini, G. Schettino, C. Jacobs, S. T. Suess

摘要:

日冕物质抛射(CME)的爆发拖曳并“打开”日冕磁场,可能导致大规模电流片的形成和磁重联的场弛豫。我们分析了在CME之后形成的射线状日冕特征的物理特征,以检查这种现象的解释是否与观测结果一致。这项研究的重点是测量射线宽度,密度过剩,和日冕速度场作为径向距离的函数。射线的形态表明,它们发生的后果Petschek的重联在大规模的电流片形成的CME的尾流。这一假设得到了流态的支持,流态通常沿着射线流出,有时也流入射线。推断的流入速度范围从3到30公里秒$^{-1}$,符合狭窄的开口角的射线,加起来几度。射线的密度比周围的日冕大一个数量级。密度过剩的测量结果进行了比较的分析模型中,Petschek的重联几何形状被应用到垂直电流片,考虑到降低的外部日冕密度和磁场与高度。模型结果与观测结果一致,揭示了射线中密度过剩的主要原因是重联流出将稠密等离子体从较低高度输送到较大高度。

英文摘要:

Eruption of a coronal mass ejection (CME) drags and "opens" the coronal magnetic field, presumably leading to the formation of a large-scale current sheet and the field relaxation by magnetic reconnection. We analyze physical characteristics of ray-like coronal features formed in the aftermath of CMEs, to check if the interpretation of this phenomenon in terms of reconnecting current sheet is consistent with the observations. The study is focused on measurements of the ray width, density excess, and coronal velocity field as a function of the radial distance. The morphology of rays indicates that they occur as a consequence of Petschek-like reconnection in the large scale current sheet formed in the wake of CME. The hypothesis is supported by the flow pattern, often showing outflows along the ray, and sometimes also inflows into the ray. The inferred inflow velocities range from 3 to 30 km s$^{-1}$, consistent with the narrow opening-angle of rays, adding up to a few degrees. The density of rays is an order of magnitude larger than in the ambient corona. The density-excess measurements are compared with the results of the analytical model in which the Petschek-like reconnection geometry is applied to the vertical current sheet, taking into account the decrease of the external coronal density and magnetic field with height. The model results are consistent with the observations, revealing that the main cause of the density excess in rays is a transport of the dense plasma from lower to larger heights by the reconnection outflow.

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