THE 3-D MAGNETIC-FIELD STRUCTURE OF AR-6659 FROM A BOUNDARY-ELEMENT METHOD SOLUTION UNDER CONSTANT-ALPHA FORCE-FREE FIELD CONDITION

Using the boundary element method (BEM), the linear force-free magneti c field above the active region NOAA 6659 on 9 June, 1991 is reconstru cted based on Huairou vector magnetograms with 180 degrees azimuth amb iguity removed. The associations of a 3B/X12 flare to the 3-D magnetic field structure are demonstrated. In particular, the following result s are revealed by this study. (a) The 3B/X12 flare is probably due to the interaction between an energetic low-laid active magnetic loop alo ng the magnetic neutral lines (thus revealing a highly sheared feature on the photosphere) and several other loops. (b) Each primary flare k ernel seen from H beta image or white light, is located at foot-points of several interacting loops. (c) The currents flowing along the acti ve low-laid loop deduced from the present computation are approximatel y 11x10(11) A, in an order consistent with that estimated from the hig h resolution observations. (d) The 3-d field distribution indicates th at only a minor portion of magnetic field lines in the delta sunspot i s connected locally and the majority of them are extended globally to the exterior of the region. This may explain the severe imbalance of m agnetic flux between opposite polarities in great delta-sunspots. The present results support the idea that excess magnetic energy is probab ly suddenly released due to reconnection at separatrices by instabilit y.