Global budget for an eruptive active region - I. Equilibrium reconstruction approach
Global budget for an eruptive active region - I. Equilibrium reconstruction approach
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DOI：
10.1051/0004-6361:20021332
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发表时间：
2002-11
影响因子：
6.5
通讯作者：
A. Bleybel;T. Amari;L. Driel-Gesztelyi;K. Leka
中科院分区：
文献类型：
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作者：
A. Bleybel;T. Amari;L. Driel-Gesztelyi;K. Leka
本文介绍了1995年10月14日发生在NOAA活动区#7912中的一次长时间耀斑的磁结构结果，该活动区是WIND航天器10月18-20日观测到的磁云的源区。使用来自成像矢量磁力仪（“IVM”）的矢量磁图，我们重建了该活动区域上方的磁场，假设其处于非线性无力状态。该重建用于确定活动区域磁场的全局特性，包括拓扑结构、磁能和相对磁螺旋度。本文还讨论了火山爆发前后的一些全球性的物理量的比较。我们发现，活动区的磁能和相对螺旋度在喷发后下降，与大量螺旋度的喷射（在磁云中）一致。我们还表明，放松后耀斑状态仍然包含非线性，是不符合泰勒的松弛理论预测的线性无力状态。这些结果与最近关于等离子体团喷射和螺旋度重新分布的数值模拟结果一致。我们建议作为一种解释，在光球场线的锚定，防止完整的级联泰勒状态，并在其中的作用功能将描述这种约束的变分制剂应派生。
We present results on the magnetic structure of NOAA Active Region #7912 which was involved in a long duration flare on 14 October 1995, and was the source region for a magnetic cloud observed by the WIND spacecraft from October 18-20. Using vector magnetograms from the Imaging Vector Magnetograph ("IVM"), we reconstruct the magnetic field above this active region, assuming it is in a non-linear force-free state. This reconstruction is used to determine global properties of the active region magnetic field including topology, magnetic energy, and relative magnetic helicity. A comparison of some global quantities before and after the eruptive event is discussed. We show that the magnetic energy and relative helicity of the active region decreased after the eruption, consistent with the ejection of a large amount of helicity ( in the magnetic cloud). We also show that the relaxed post-flare state still contains nonlinearities and is not consistent with a linear force-free state as predicted by Taylor's theory of relaxation. These results agree with those of recent numerical simulations concerning plasmoid ejection and helicity redistribution in the disruption of magnetic configurations. We propose as an explanation that the anchoring of field lines in the photosphere prevents a full cascade to the Taylor state, and that a variational formulation in which the action functional would describe this constraint should be derived.