X级耀斑过程中的磁剪切变化(英文)

MAGNETIC SHEAR VARIATION DURING X-CLASS FRARES

通过对活动区NOAA 6891中三个X级耀斑前后的向量磁场分析 ,研究耀斑发生条件与耀斑发生前后横向磁场和磁剪切变化的关系。我们发现与Hagyard的耀斑发生条件不同的是 ,强的横向磁场和磁剪切不是活动区中耀斑发生的充要条件。我们的结果表明 ,活动区NOAA 6891 1 991年 30日的耀斑发生在横向磁场和磁剪切剧烈下降后。尽管 1 0月 2 7日的耀斑发生后横向磁场和磁剪切变化很大 ,但由于有新磁流浮现 ,造成磁中性线的改变 ,使得横向磁场和磁剪切变化与耀斑发生的联系变得比较复杂。

Based on the vector magnetogram analysis during the three X class flares in active region NOAA 6891, the variation of magnetic transverse field and shear (MTFS) are investigated. In contrast to the flare conditions prescribed by Hagyard, we find the strong MTFS are not the sufficient condition for flare to occur in this active region. Our results show that the 3B/X2.5 flare on Oct. 30 occurred after dramatic decrease of MTFS at the flaring region. Although the change of MTFS in the photosphere existed just after the initial brightening of the flare on Oct. 27, the reason for the change is ambiguous due to the new flux emergence.