Title: Coronal Mass Ejections, Central axial field direction in magnetic clouds and Geomagnetic Storms
Author: Liu Siqing
Affil: Center of space science and apply research, Chinese Academy of Science
Email: Liusq@earth.sepc.ac.cn
Authors: Gong jiancun
Affils: Center of space science and apply research, Chinese Academy of Science
Abstract: In this paper, two interesting solar events that took place in July 14, 2001 and 12 Sept., 2001 were studied. Two brilliant full-halo coronal mass ejections (CME) were recorded by the Coronagraphs on SOHO during these two periods. The first CME accompany with a X5.7 x-ray flare that is one of the most powerful solar flares of the current solar cycle. In the event of Sept., there was a filament collapsed, and a powerful x-ray solar flare produced. But the influences of these two solar events are quite distinct from each other. The first CME led a extreme geomagnetic storm, but the second one just made geomagnetic field active. Compared with these two events, we find that an important reason of this difference is the solar magnetic field of the solar source. We know, long intervals of large southward interplanetary magnetic field (IMF) are the primary cause geomagnetic storms. These two cases show the central axial field direction in magnetic cloud is related to magnetic field structure of source region on the disc. And the structure of MC is the reason of different southward IMF.