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arXiv 1908.06360astro-ph.SRphysics.space-ph
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NOAA 12673活动区早期磁通量绳的形成

Formation of a Magnetic Flux Rope in the Early Emergence Phase of NOAA Active Region 12673

Lijuan Liu, Xin Cheng, Yuming Wang, Zhenjun Zhou

摘要:

在这项工作中,我们调查的形成磁通量绳(MFR)以上的中心极性反转线(PIL)的NOAA活动区12673在其早期出现阶段。通过对光球矢量磁场、极紫外(EUV)和紫外(UV)图像、外推的三维非线性无力场(NLFFF)以及光球运动的分析,发现随着中心区域不同双极的相继出现,共轭极性发生分离,导致非共轭相反极性之间发生碰撞。近势环首先出现在PIL上方,然后在碰撞位置被剪切并合并,如2017年9月4日连续EUV S形的出现所证明的,这也表明MFR的形成。3D NLFFF进一步揭示了MFR的逐渐积累,伴随着两个细长的秃斑(BP)在碰撞位置和一个非常低的双曲线通量管配置之间的BP的外观。最终MFR具有相对稳定的轴向通量和平均扭转数,分别约为$2.1\times 10^{20}$ ~Mx和-1.5。当碰撞发生时,在BPs附近发现剪切运动,同时观察到通量抵消和紫外线增亮,这表明一个名为“碰撞剪切”的过程的发展(首先由Chintzoglou等人确定。结果清楚地表明,MFR是由“碰撞剪切”形成的,即,通过在它们出现期间由非共轭相反极性之间的碰撞驱动的剪切和通量抵消。

英文摘要:

In this work, we investigate the formation of a magnetic flux rope (MFR) above the central polarity inversion line (PIL) of NOAA Active Region 12673 during its early emergence phase. Through analyzing the photospheric vector magnetic field, extreme ultraviolet (EUV) and ultraviolet (UV) images, extrapolated three-dimensional (3D) non-linear force-free fields (NLFFFs), as well as the photospheric motions, we find that with the successive emergence of different bipoles in the central region, the conjugate polarities separate, resulting in collision between the non-conjugated opposite polarities. Nearly-potential loops appear above the PIL at first, then get sheared and merge at the collision locations as evidenced by the appearance of a continuous EUV sigmoid on 2017 September 4, which also indicates the formation of an MFR. The 3D NLFFFs further reveal the gradual buildup of the MFR, accompanied by the appearance of two elongated bald patches (BPs) at the collision locations and a very low-lying hyperbolic flux tube configuration between the BPs. The final MFR has relatively steady axial flux and average twist number of around $2.1\times 10^{20}$~Mx and -1.5, respective. Shearing motions are found developing near the BPs when the collision occurs, with flux cancellation and UV brightenings being observed simultaneously, indicating the development of a process named as "collisional shearing" (firstly identified by Chintzoglou et al. 2019). The results clearly show that the MFR is formed by "collisional shearing", i.e., through shearing and flux cancellation driven by the collision between non-conjugated opposite polarities during their emergence.

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