H alpha and soft X-ray brightening events caused by emerging flux

By using Yohkoh soft X-ray images, vector magnetograms, and Her filtergrams , the brightening event that occurred on 1994 May 18 has been studied in de tail. It occurred in a nearly potential large-scale magnetic configuration as shown by the comparison between the magnetic extrapolation (linear force -free field) and the large-scale soft X-ray loops. This event is related to the emergence of a new magnetic flux of about 3 x 10(20) Mr. The impulsive enhancement of the emerging flux occurs about 20 minutes before the peaks of the Ha and soft X-ray brightening and lasts for about 10 minutes. This b rightening may be a signature of reconnection taking place between the pree xisting nonpotential loops and the new emerging small loops. The magnetic e nergy provided by reconnection is likely to be stored in the nonpotential l oops and the emerging flux as implied by the vector magnetograms. By using the electron temperature and the electron density of the brightening event derived from the analysis of the Yohkoh data, an energy budget has been est imated. The result indicates that the energy needed can be reasonably provi ded by magnetic reconnection.