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A Solar Flare Disturbing a Light Wall above a Sunspot Light Bridge  

Yijun Hou   Submitted: 2016-10-04 01:43

With the high-resolution data from the Interface Region Imaging Spectrograph, we detect a light wall above a sunspot light bridge in the NOAA active region (AR) 12403. In the 1330 Å slit-jaw images, the light wall is brighter than the ambient areas while the wall top and base are much brighter than the wall body, and it keeps oscillating above the light bridge. A C8.0 flare caused by a filament activation occurred in this AR with the peak at 02:52 UT on 2015 August 28, and the flare's one ribbon overlapped the light bridge, which was the observational base of the light wall. Consequently, the oscillation of the light wall was evidently disturbed. The mean projective oscillation amplitude of the light wall increased from 0.5 to 1.6 Mm before the flare and decreased to 0.6 Mm after the flare. We suggest that the light wall shares a group of magnetic field lines with the flare loops, which undergo a magnetic reconnection process, and they constitute a coupled system. When the magnetic field lines are pushed upward at the pre-flare stage, the light wall turns to the vertical direction, resulting in the increase of the light wall's projective oscillation amplitude. After the magnetic reconnection takes place, a group of new field lines with smaller scales are formed underneath the reconnection site, and the light wall inclines. Thus, the projective amplitude notably decrease at the post-flare stage.

Authors: Yijun Hou, Jun Zhang, Ting Li, Shuhong Yang, Leping Li, and Xiaohong Li
Projects: None

Publication Status: Published in ApJL.
Last Modified: 2016-10-05 11:13
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Flux rope proxies and fan-spine structures in active region NOAA 11897  

Yijun Hou   Submitted: 2016-07-06 08:35

Context. Flux ropes are composed of twisted magnetic fields and are closely connected with coronal mass ejections (CMEs). The fan-spine magnetic topology is another type of complex magnetic fields. It has been reported by several authors, and is believed to be associated with null-point-type magnetic reconnection. Aims. We try to determine the number of flux rope proxies and reveal fan-spine structures in the complex active region (AR) NOAA 11897. Methods. Employing the high-resolution observations from the Solar Dynamics Observatory (SDO) and the Interface Region Imaging Spectrograph (IRIS), we statistically investigated flux rope proxies in NOAA AR 11897 from 14 November 2013 to 19 November 2013 and display two fan-spine structures in this AR. Results. For the first time, we detect flux rope proxies of NOAA 11897 for a total of 30 times in four different locations during this AR's transference from solar east to west on the disk. Moreover, we notice that these flux rope proxies were tracked by active or eruptive material of filaments 12 times, while for the remaining 18 times they appeared as brightenings in the corona. These flux rope proxies were either tracked in both lower and higher temperature wavelengths or only detected in hot channels. None of these flux rope proxies was observed to erupt; they faded away gradually. In addition to these flux rope proxies, we detect for the first time a secondary fan-spine structure. It was covered by dome-shaped magnetic fields that belong to a larger fan-spine topology. Conclusions. These new observations imply that many flux ropes can exist in an AR and that the complexity of AR magnetic configurations is far beyond our imagination.

Authors: Y. J. Hou, T. Li and J. Zhang
Projects: None

Publication Status: 8 pages, 8 figures, Accepted for publication in A&A
Last Modified: 2016-07-06 10:34
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Light walls around sunspots observed by the Interface Region Imaging Spectrograph  

Yijun Hou   Submitted: 2016-04-07 06:27

The Interface Region Imaging Spectrograph (IRIS) mission provides high-resolution observations of the chromosphere and transition region. Using these data, some authors have reported the new finding of light walls above sunspot light bridges. We try to determine whether the light walls exist somewhere else in active regions in addition to the light bridges. We also examine how the material of these walls evolves. Employing six months of (from 2014 December to 2015 June) high tempo-spatial data from the IRIS, we find many light walls either around sunspots or above light bridges. For the first time, we report one light wall near an umbral-penumbral boundary and another along a neutral line between two small sunspots. The former light wall has a multilayer structure and is associated with the emergence of positive magnetic flux in the ambient negative field. The latter light wall is associated with a filament activation, and the wall body consists of the filament material, which flowed to a remote plage region with a negative magnetic field after the light wall disappeared. These new observations reveal that these light walls are multilayer and multithermal structures that occur along magnetic neutral lines in active regions.

Authors: Y. J. Hou, T. Li, S. H. Yang and J. Zhang
Projects: None

Publication Status: Accepted for publication in A&A Letters
Last Modified: 2016-04-07 19:22
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Abstracts by Author
A Solar Flare Disturbing a Light Wall above a Sunspot Light Bridge
Flux rope proxies and fan-spine structures in active region NOAA 11897
Light walls around sunspots observed by the Interface Region Imaging Spectrograph

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