Active region helicity evolution and related coronal mass ejection activity Original Research Article

The computation of magnetic helicity has become increasingly important in the studies of solar activity. Observations of helical structures in the solar atmosphere, and their subsequent ejection into the interplanetary medium, have resulted in considerable interest to find the link between the amount of helicity in the coronal magnetic field and the origin of coronal mass ejections (CMEs), which provide a natural method to remove helicity from the corona. Recent works have endeavored to find the source of helicity to explain the observed CME activity in specific cases. The main candidates being differential rotation, shear motions or a transfer of helicity from below the photosphere into the corona. We study an active region for several rotations during 1997 and 1998 to investigate the relative importance of these mechanisms. We find that photospheric differential rotation cannot provide the required magnetic helicity to the corona and the ejected CMEs. Localized photospheric motions can provide a larger helicity flux, though still not sufficient.