STRUCTURE, STABILITY, AND EVOLUTION OF MAGNETIC FLUX ROPES FROM THE PERSPECTIVE OF MAGNETIC TWIST
STRUCTURE, STABILITY, AND EVOLUTION OF MAGNETIC FLUX ROPES FROM THE PERSPECTIVE OF MAGNETIC TWIST
复制标题
从磁扭角度看磁通绳的结构、稳定性和演化
DOI：
10.3847/0004-637x/818/2/148
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发表时间：
2016-02-20
影响因子：
4.9
通讯作者：
Wiegelmann, Thomas
中科院分区：
文献类型：
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作者：
Liu, Rui;Kliem, Bernhard;Wiegelmann, Thomas
我们研究了2013年8月10-12日期间NOAA活动区(AR)11817的演化，当时它形成了一个复杂的场结构，产生了四个受限耀斑，然后是两个爆发耀斑。这些C级及以上的耀斑都与位于主极性反转线上的磁通量绳(MFR)有关，那里存在剪切和会聚的光球流。在非线性无力场模型的辅助下，我们通过映射磁连接性和计算每个单独场线的扭转数T-w来识别MFR。MFR是中等扭曲的(垂直条形T-W垂直条形)，有一个明确的高挤压因子Q的边界。我们发现极值垂直条形T-W垂直条形的场线是绳轴的可靠代表，MFR的峰值垂直条形T-W垂直条形在每次耀斑前半小时内暂时增加，而对于受限耀斑和爆发耀斑来说，它在耀斑峰值之后减小。由于耀斑的量适中，而MFR的体积相对较小，这种耀斑前垂直条形T-W垂直条形的增加对AR的自由磁能或整个区域的其他参数影响不大，而耀斑后的减少明显与耀斑引起的整个区域的自由磁能的递减有关。我们认为，T-w可以作为一个有用的参数来预测喷发的开始，从而预测由此产生的空间天气效应。螺旋扭结不稳定性被认为是所考虑的耀斑的主要候选爆发机制。
We investigate the evolution of NOAA Active Region (AR) 11817 during 2013 August 10-12, when it developed a complex field configuration and produced four confined, followed by two eruptive, flares. These C-and-above flares are all associated with a magnetic flux rope (MFR) located along the major polarity inversion line, where shearing and converging photospheric flows are present. Aided by the nonlinear force-free field modeling, we identify the MFR through mapping magnetic connectivities and computing the twist number T-w for each individual field line. The MFR is moderately twisted (vertical bar T-w vertical bar < 2) and has a well-defined boundary of high squashing factor Q. We found that the field line with the extremum vertical bar T-w vertical bar is a reliable proxy of the rope axis, and that the MFR's peak vertical bar T-w vertical bar temporarily increases within half an hour before each flare while it decreases after the flare peak for both confined and eruptive flares. This pre-flare increase in vertical bar T-w vertical bar has little effect on the AR's free magnetic energy or any other parameters derived for the whole region, due to its moderate amount and the MFR's relatively small volume, while its decrease after flares is clearly associated with the stepwise decrease in the whole region's free magnetic energy due to the flare. We suggest that T-w may serve as a useful parameter in forewarning the onset of eruption, and therefore, the consequent space weather effects. The helical kink instability is identified as the prime candidate onset mechanism for the considered flares.