Magnetic topology in 1998 November 5 two-ribbon flare AS inferred from ground-based observations and linear force-free field modeling

We analyzed the three-dimensional structure of the linear force-free magnetic field. A longitudinal magnetogram of Active Region NOAA 8375 has been used as the photospheric boundary condition. The 1998 November 5 2B/M8.4 two-ribbon flare can be explained in the framework of quadrupolar reconnection theory: the interaction of two closed magnetic loops that have a small spatial angle. The energy derived from soft X-ray telescope (SXT)/Yohkoh data (3-6 × 10³⁰ ergs) is 1 order of magnitude higher than the lower limit of flare energy predicted by Melrose's model. The latter estimation was made using the linear force-free extrapolation. It was suggested that, taking into account the nonlinear character of the observed magnetic field, we can increase the lower limit of the magnetic energy stored in the studied magnetic configuration. The revealed magnetic configuration allows us to understand the observed location and evolution of the flare ribbons and the additional energy released during the gradual phase of the flare, as well. Besides, reconnection of closed magnetic loops can logically explain the connection between a two-ribbon flare and a giant X-ray postflare arch, which usually is observed after the flare onset. We emphasize that unlike the Kopp and Pneuman configuration, the model discussed here does not necessarily require destabilization and opening of the magnetic field.