We studied the background field for 60 two-ribbon flares of M-and-above classes during 2011–2015. These flaresudare categorized into two groups, i.e., eruptive and confined flares, based on whether a flare is associated with audcoronal mass ejection or not. The background field of source active regions is approximated by a potential fieldudextrapolated from the Bz component of vector magnetograms provided by the Helioseismic and Magnetic Imager.udWe calculated the decay index n of the background field above the flaring polarity inversion line, and defined audcritical height hcrit corresponding to the theoretical threshold (ncrit = 1.5) of the torus instability. We found that hcritudis approximately half of the distance between the centroids of opposite polarities in active regions and that theuddistribution of hcrit is bimodal: it is significantly higher for confined flares than for eruptive ones. The decay indexudincreases monotonously with increasing height for 86% (84%) of the eruptive (confined) flares but displays audsaddle-like profile for the rest, 14% (16%), which are found exclusively in active regions of multipolar fieldudconfiguration. Moreover, n at the saddle bottom is significantly smaller in confined flares than that in eruptive ones.udThese results highlight the critical role of background field in regulating the eruptive behavior of two-ribbon flares
展开▼
机译:我们研究了2011-2015年间60个M级及以上级别的两个功能区耀斑的背景场。这些耀斑根据耀斑是否与冠状体质量喷射有关而分为两类,即爆发性和局限性耀斑。源活动区域的背景场近似为由Helioseismic and Magnetic Imager提供的矢量磁图的Bz分量势能场 udex推算得出的。 ud我们计算了耀斑极性反转线上方的背景场的衰减指数n,并定义了 u临界高度hcrit对应于环面不稳定性的理论阈值(ncrit = 1.5)。我们发现,hcrit在活动区域中的极性相反的质心之间的距离大约为一半,并且hcrit的 ud分布是双峰的:局限性耀斑比喷发性耀斑明显更高。衰减指数 ud随高度的增加而单调上升,占爆发性(受限)耀斑的86%(84%),但其余部分显示出 udsaddle样的轮廓,占14%(16%),仅存在于活动区域多极场 udconfiguration。此外,密闭火炬中鞍底部的n明显小于爆发性火炬中的n。 ud这些结果凸显了背景场在调节两个丝带火炬的爆发行为中的关键作用。
展开▼