An analysis of photospheric vector magnetograms, Hα images and soft X-ray images in a superactive region NOAA 7321

Abstract

Based on the photospheric vector magnetograms taken at Huairou Solar Observing Station (HSOS), Hα images taken at Hiraiso Solar Terrestrial Research Center of Communication Research Laboratory, soft X-ray images taken by Yohkoh and an extrapolation method, the magnetic field structures and some active phenomena of the active region AR 7321 around 04:12 UT on 27 October 1992 are analyzed in this paper. A divergence of the transverse magnetic field, located at a newly formed spot, was found. At least four highly sheared magnetic field systems separately spread from this divergence to four other sites around this divergence. Vertical current concentrations are upward in this region and downward in the other four sites, and the corresponding Hα bright patches and soft X-ray bright loops coincide with these structures, confirming the existence of these four systems. The extrapolated magnetic force lines reconstructed by the Boundary Element Method (BEM), force-free field assumption, and boundary condition of observed photospheric vector magnetic field, coincide in space with the Hα bright patches and soft X-ray bright loops, showing that this extrapolation method is very effective and suggesting that the Hα bright patches and soft X-ray bright loops in this case represent the magnetic field structures in the upper atmosphere of the Sun.