fl092.hanaoka04 Posted: 12-Dec-92 Updated: 31-Jul-93, 26-Nov-93 Events specified: flare on 15-Jul-92 at 03:51 UT
Y. Hanaoka and Nobeyama Radioheliograph group SXT team and Magnetograph observers
Motivation: It is considered that interactions between magnetic loops are one of the mechanisms which cause flares, but it is rare that we really see interacting loops. A C5.3 flare, which occurred at 03:51 UT on July 15, 1992 in the region NOAA7226, is a very good example of a flare caused by interacting loops. On July 14, or about 24 hours before the flare, two parallel bright coronal loops seen in SXT images in the region NOAA7226 suggest that the magnetic fields are only weakly sheared. There was a spot near one of the footpoints of one of the loops. This spot moved rapidly and one of the loops were dragged by the spot, and magnetic shear was rapidly inceased. The farside footpoint from the spot of the dragged loop moved toward the opposite polarity footpoint of the other loop, and finally these two opposite polarity footpoints collided together and flared up. This flare was also observed by the Nobeyama Radioheliograph. The radio images are peculiar because they do not show any evidence of non-thermal radiation, which we can find in almost all flares.
Method: We analyze the SXT images of the flare with the radio images, and derive physical parameters.
Update 26-Nov-93
A paper about my proposal fl092.hanaoka04 has already been accepted and it is now in press (ApJ Letters).
Update 31-Jul-93
I am now writing a paper on this topic, and the following is the temporal abstract of the paper.
Title: A flare caused by interacting coronal loops
PI and Collaborators: Y. Hanaoka and SXT people
Abstract: The observation of a flare on July 15, 1992 by the Soft X-ray Telescope on board the Yohkoh satellite manifested that the energy build-up in the corona was caused by the increasing shear of the magnetic field due to the photospheric motion, and that the flare occurred by the interaction of the two sheared coronal loops. About 24 hours before the flare, there are two nearly parallel coronal loops, which suggest that the magnetic fields are only weakly sheared. After that time, a rapid spot motion with the velocity of 0.4 kms$^{-1}$ was observed, and the coronal loops are changed to a sheared structure by this motion. Finally, a flare occurred at the sheared loops. Such a scenario of the energy build-up and release processes have been suggested from the various indirect evidence. However, the SXT, which takes both the soft X-ray and optical pictures, shows that the photospheric motion actually produces the sheared coronal loop structure for the first time. Furthermore, the sturucture of the interacting coronal loops in the SXT images of the flare proved the propriety of the model conjectured by theorists.