A Flare Due to the Interaction of a Small Loop and a Large Loop

A C6.0 GOES X-ray-class flare which occurred at 05:32 UT on 5 September 1994 in the active region NOAA 7773 is analyzed in this paper. We found that this flare was triggered by the interaction of a small loop and a large loop. The small loop connected a decaying magnetic flux, not an emergence of magnetic flux as usually shown. These two loops were matched well by the extrapolated force-free field lines based on the Boundary Element Method and the boundary condition of the observed photospheric vector magnetic field. Soft X-ray observation showed that these two loops gradually merged to become one, and the soft X-ray intensity increased during the merging process, agreeing with the simulated results of I-type coalescence derived by Fushiki and Sakai (1995) and Sakai and Fushiki (1995).