Relation between magnetic helicity injection and flare activities
Abstract
Recent studies suggest that the magnetic helicity is a good indecater of the stored magnetic free energy in an active region. This stored energy is released as flares, but the physical relationship between the helicity and the flares is still unknown. In this paper, we show our analysis of the magnetic helicity/energy injection into the several active regions, including NOAA 8100 which is known as a source of many coronal activities such as flares and coronal mass ejections. To measure the helicity/energy injection, we used our new method which can derive the injections not only by the shear motion but also by the emerging motion based on the magnetograph observations. The data sets we used were taken by SOHO/MDI and by the Solar Flare Telescope (SFT) at NAOJ in Mitaka, Tokyo. In AR 8100, Eleven major flares greater than GOES X-ray class C8.0 were observed in this region. Five of the events were concentrated in the eastern part of the active region where strong shear motion was seen. It is found that these five events coccured from 20:00 UT on Nov. 3 to 4:00 UT on Nov. 4 about half a day after the helicity injection rate (sum of the emergence and shear injections) changed its sign from positive to negative at 8:00 UT on Nov 3. This tendency is also true for other three events which occurred in the western part, but the helicity injection was mainly due to the emerging flux activities. We found that this relationship between the helicity injection and the flares was also true for the other analysed active regions. This result suggests that the sign-reversal of the helicity injection rate is a key signature of flare activities.
- Publication:
-
34th COSPAR Scientific Assembly
- Pub Date:
- 2002
- Bibcode:
- 2002cosp...34E2324Y