Evolution of vector magnetic fields and vertical currents and their relationship with solar flares in AR 5747

Abstract

NOAA 5747 was a flare-productive active region during its transit across the solar disk in October 1989. After the resolution of the 180° ambiguity of the transverse field synthetically, and transformation of vector magnetograms from the image plane to the heliographic frame, we have determined the distribution of the photospheric vertical electric current density in the active region. By analyzing the evolution of vector magnetograms and vertical current over a 6-day period (October 17–22) in the active region, we get the following results: (1) Two magnetic fluxes of opposite polarities emerged synchronously with their separating motion, one of which converged with an old magnetic structure and caused a number of flares. (2) There appeared a new current system, with the emergence of the fluxes. (3) The initial Hβ bright kernels occurred in the vicinity of the neutral line of vertical current (J _z = 0) with a steep gradient, but not just on the sites of vertical current peaks. (4) The flares were probably triggered by the interaction between the new emerging electric current system and old current system.