X-type interactions of loops in the flare of 25 September 1997

Abstract

The evolution and properties of the GOES C7.2 class solar flare observed in the NOAA 8088 active region on 25 September 1997 were studied with data taken by the Wroclaw Large Coronagraph/MSDP in Hα, Yohkoh/SXT and GOES X-rays as well as SOHO/MDI magnetic and SOHO/EIT ultraviolet observations. The observed properties of the flare are consistent with a model in which the releases of the energy were caused by two successive X-type interactions of an expanding loop with two higher located, nearly parallel loops. Before the second interaction the lower loop was pushed from below by the eruption of the magnetic field manifested by eruption of a system of Hα threads. The total energy stored in the magnetic fields of three interacting loops, E_magn ~ 1 * 10(31) erg, was almost one order greater than the whole thermal energy contained in the loops E_tot ~ 1.2 * 10(30) erg. While the flare occurred in a stable system of magnetic loops, which apparently survived the flare, we find that the thermal energy was emitted at a cost of the annihilation of a fraction of the magnetic fields in the turbulent kernel.