The Automatic Predictability of Super Geomagnetic Storms from halo CMEs associated with Large Solar Flares |
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| Authors: | Hui Song Vasyl Yurchyshyn Guo Yang Changyi Tan Weizhong Chen Haimin Wang |
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| Institution: | 1. Center for Solar-Terrestrial Research, New Jersey Institute of Technology, Newark, NJ, 07102, U.S.A.
2. Big Bear Solar Observatory, 40386 North Shore Lane, Big Bear City, CA, 92314, U.S.A.
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| Abstract: | We investigate the relationship between magnetic structures of coronal mass ejection (CME) source regions and geomagnetic
storms, in particular, the super storms when the D
st index decreases below −200 nT. By examining all full halo CMEs that erupted between 1996 and 2004, we selected 73 events
associated with M-class 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 orientation angle was found to be southward. In the case of intense and moderate storms (D
st≥ −200 nT), 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 prediction of the occurrence of large X-class flares and super geomagnetic
storms. |
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