Dynamics of small-scale magnetic fields before small and large solar flares

A. Borovik, A. Zhdanov
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Abstract

We have examined the dynamics of the longitudinal magnetic field of active region NOAA 12673, using data from the Solar Dynamics Observatory (SDO). During the passage of the active region (AR) across the solar disk, its spots and background fields showed complex motion trajectories, and numerous small-scale short-lived local polarity inversion lines (LPILs) were formed when new magnetic fluxes appeared in the AR and came closer to fields of opposite polarity. The length of LPILs was less than 15.000 km (~20 arcsec); their lifetime was several hours. Study of the flare activity of NOAA 12673 has shown that low-power flares (optical class S, area ˂2 sq. degrees) generally occur near LPILs. Before small flares and the September 06, 2017 large flare (optical importance 3B, X-ray class X9.3), in limited sites of local and main polarity inversion lines there were shear stresses and an increase in the magnetic field gradient: in the region of low-power flares, to 1.3–1.5 G/km; in the region of the large flare, 3–3.5 G/km. The results obtained suggest that the longitudinal magnetic field behaves similarly before both small and large flares.
小型和大型太阳耀斑前的小尺度磁场动力学
我们利用太阳动力学天文台(SDO)的数据研究了活动区 NOAA 12673 的纵向磁场动态。在活动区(AR)穿过太阳盘的过程中,其磁斑和背景磁场呈现出复杂的运动轨迹,当新磁通出现在活动区并靠近极性相反的磁场时,就会形成许多小尺度的短时局域极性反转线(LPIL)。LPIL 的长度小于 15.000 千米(约 20 弧秒);其寿命为数小时。对 NOAA 12673 耀斑活动的研究表明,低功率耀斑(光学等级 S,面积 ˂2 平方度)通常发生在 LPIL 附近。在小耀斑和2017年9月6日的大耀斑(光学重要性3B,X射线等级X9.3)之前,在局部和主极性反转线的有限位置存在剪应力和磁场梯度的增加:在小功率耀斑区域,为1.3-1.5 G/km;在大耀斑区域,为3-3.5 G/km。所得结果表明,纵向磁场在小耀斑和大耀斑之前的表现类似。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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