PRIMARY STUDYING OF RELATIONSHIP AMONG CORONAL MASS EJECTIONS, Bs EVENTS AND GEOMAGNETIC STORMS

摘要

Two interesting solar events that took place in July 14, 2000 and Sept. 12, 2000 were studied in this paper. Two brilliant full-halo coronal mass ejections (CME) were recorded by the Coronagraphs on SOHO during these two events. The first CME accompany with a X5.7 x-ray flare which is one of the most powerful solar flares in the current solar cycle. A filament disappearance and a powerful x-ray solar flare were observed in the second event. However, the effects of these two solar events are quite different from each other. An extreme geomagnetic storm was triggered by the first CME, but the second one just led geomagnetic disturbances. It is well known that long duration of large southward interplanetary magnetic field (Bs event) is the primary cause of geomagnetic storms. Comparing these two events, we find that the IMF structures of the associated CME events are different. It is shown that the central axial field direction in magnetic cloud (MC) is related to magnetic field structure of the source region on the disc. Therefore we can predict the possibility of Bs events through the magnetic structure on the photosphere, because of the variation of IMF Bz can be deduced by MC Model.