The Automatic Predictability of Super Geomagnetic Storm from Halo CMEs Associated with Large Solar Flares

We investigate the relationship between magnetic structures of CME source regions and geomagnetic storms, in particular the super storms when the Dst index decreases below -200nT. By examining all full halo CMEs that erupted between 1996 and 2004, we selected 73 events associated with M and X-class solar flares, which have a clearly identifiable source region. By analyzing daily full disk MDI magnetograms we found that the horizontal gradient of the line-of-sight magnetic field is a viable parameter to identify a flaring magnetic neutral line and thus can be used to predict the possible source region of CMEs. The accuracy of this prediction is about 75%, especially for those associated with X-class flares (up to 89%).The mean orientation of the magnetic structures of source regions was derived and characterized by the orientation angle θ , which is defined to be ≤ 90◦ in the case of the southward orientation and ≥ 90◦, when the magnetic structure is northwardly oriented. The orientation angle was calculated as the median orientation angle of extrapolated field lines relative to the flaring neutral line. We report that for about 92% of super storms (12 out of 13 events) the orientations angle was found to be southward. In the case of intense and moderate storms (Dst ≥ -200nT), the relationship is less pronounced (70%, 21 out of 30 events). Our findings demonstrate that the approach presented in this paper can be used to perform an automatic predictions of the occurrence of large X-class flares and super geomagnetic storms.