Compact solar UV burst triggered in a magnetic field with a fan-spine topology
Compact solar UV burst triggered in a magnetic field with a fan-spine topology
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DOI：
10.1051/0004-6361/201730830
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发表时间：
2017-09-01
影响因子：
6.5
通讯作者：
Huang, Y. -M.
中科院分区：
文献类型：
--
作者：
Chitta, L. P.;Peter, H.;Huang, Y. -M.
上下文太阳紫外线（UV）爆发是小尺度的特征，表现出间歇性的增亮，被认为是由于磁重联。它们在色球层和过渡区，特别是在活动区被大量观测到。我们详细研究了紫外线爆发有关的磁功能，是平流的护城河流从太阳黑子朝向孔。运动特征是寄生的，因为它的磁极性与斑点和孔隙的磁极性相反。这种简单的光球磁场分布允许一个明确的解释的磁性几何形状，导致所观察到的紫外爆发的发病。我们使用紫外光谱和狭缝颚观测接口区域成像光谱仪（IRIS），以确定和研究色球和过渡区的光谱特征，说紫外线爆发。为了研究紫外线爆发周围的磁拓扑结构，我们使用了一个两小时长的时间序列，同时从日震和磁成像仪（HMI）的视线磁图，并通过磁摩擦弛豫技术进行数据驱动的三维磁场外推。我们可以将紫外线爆发特征与大气成像组件（AIA）观测到的上覆极紫外线（EUV）日冕环联系起来。紫外线爆发显示出各种极宽的谱线轮廓，表明等离子体流有时超过+/- 200 km s（-1）。整个结构被分为两个空间上不同的区域，主要是向上和向下流动。磁场外推显示了一个持久的风扇脊柱磁拓扑结构在紫外线爆发。相关联的三维磁零点存在于光球上方约500公里的高度，并与观测到的紫外线爆发共空间演化。冕环足点的极紫外辐射与下伏紫外爆发的演化密切相关。零点周围的磁场被光球运动剪切，触发磁场重联，最终为观测到的紫外线爆发提供动力，并为覆盖的日冕环提供能量。零点的位置表明爆发是在太阳色球层的低层触发的。
Context. Solar ultraviolet (UV) bursts are small-scale features that exhibit intermittent brightenings that are thought to be due to magnetic reconnection. They are observed abundantly in the chromosphere and transition region, in particular in active regions.Aims. We investigate in detail a UV burst related to a magnetic feature that is advected by the moat flow from a sunspot towards a pore. The moving feature is parasitic in that its magnetic polarity is opposite to that of the spot and the pore. This comparably simple photospheric magnetic field distribution allows for an unambiguous interpretation of the magnetic geometry leading to the onset of the observed UV burst.Methods. We used UV spectroscopic and slit-jaw observations from the Interface Region Imaging Spectrograph (IRIS) to identify and study chromospheric and transition region spectral signatures of said UV burst. To investigate the magnetic topology surrounding the UV burst, we used a two-hour-long time sequence of simultaneous line-of-sight magnetograms from the Helioseismic and Magnetic Imager (HMI) and performed data-driven 3D magnetic field extrapolations by means of a magnetofrictional relaxation technique. We can connect UV burst signatures to the overlying extreme UV (EUV) coronal loops observed by the Atmospheric Imaging Assembly (AIA).Results. The UV burst shows a variety of extremely broad line profiles indicating plasma flows in excess of +/- 200 km s(-1) at times. The whole structure is divided into two spatially distinct zones of predominantly up-and downflows. The magnetic field extrapolations show a persistent fan-spine magnetic topology at the UV burst. The associated 3D magnetic null point exists at a height of about 500 km above the photosphere and evolves co-spatially with the observed UV burst. The EUV emission at the footpoints of coronal loops is correlated with the evolution of the underlying UV burst.Conclusions. The magnetic field around the null point is sheared by photospheric motions, triggering magnetic reconnection that ultimately powers the observed UV burst and energises the overlying coronal loops. The location of the null point suggests that the burst is triggered low in the solar chromosphere.