Relation between magnetic helicity injection and flare activities in active region NOAA 8100 Original Research Article

The analysis of the magnetic helicity injection into active region NOAA 8100 is shown. This region is known as a source of many coronal activities such as flares. It is found that most of the flare events occurred about half a day after the helicity injection rate changed its sign. And the positions of Hα emission in flares well correspond to the helicity inversion lines in space. These results suggest that the sign-reversal of the helicity injection rate is a key signature of flare activities.