A FLARE CAUSED BY INTERACTING CORONAL LOOPS

The observation of a flare on 1992 July 15 with the Soft X-Ray Telescope (SXT) on board the Yohkoh satellite shows that the energy buildup in the corona was caused by the increasing shear of the magnetic field due to the photospheric flow and that the hare occurred through the interaction of sheared coronal loops. About 24 hr before the flare, the coronal loops were only weakly sheared. After that time, a rapid spot motion with the velocity of 0.25 km s(-1) was observed, and the coronal loops were changed to a sheared structure by this motion. Finally, a flare occurred at the intersection of the sheared loops. Such a scenario of the energy buildup and release processes has been suggested from the various indirect evidence. However, the SXT, which takes both soft X-ray and optical pictures, shows for the first time that the photospheric motion actually produces the sheared coronal loop structure. Furthermore, the observational results of the flare prove the validity of the loop-loop interaction model for flares.