An analysis of a solar active region that produced many CMEs

Abstract

In April and May of 1998, six large burst events occurred one after the other in the active region AR8210. We have collected the data of this active region, including its soft X-rays, ultraviolet radiation, radio type-II and -IV bursts as well as its radioheliograph observations. It is found that the process of energy accumulation was rapid and the time profiles of three soft X- ray bursts exhibited a certain similarity. When coronal mass ejections (CMEs) took place, the magnetic loops in this active region were only partially open and they soon contracted to become a closed loop. Under the bombardment of non-thermal electrons, the active region was again heated and it produced intense X-ray bursts as well as type-II and -IV bursts. The weak part of the magnetic loop was like a volcanic crater from which CMEs can easily erupt again. The turn-off point, where non-thermal and thermal processes intersect, was found: on the SXR time profile it is a point of sudden change of slope, and type-III bursts, that successively occur in various layers of the corona, may be taken to be convincing evidence of the occurrence of CMEs and also a criterion for estimating the velocity of the CMEs.