Physics of interplanetary magnetic flux ropes: Toward prediction of geomagnetic storms

The purpose of this review is to examine the possibility of predicting large geomagnetic storms from solar observations. We focus on three topics: (1) the relationship between coronal mass ejections and interplanetary magnetic flux ropes (hereinafter called flux ropes for simplicity), (2) the role of flux ropes in geomagnetic storms, and (3) further studies needed for improving our ability to predict geomagnetic storms based on our knowledge of flux ropes. Evidence is presented that the magnetic structures of flux ropes are strongly controlled by large-scale magnetic fields in the solar source regions of coronal mass ejections. This relationship suggests the possibility of predicting the variations in interplanetary magnetic fields based on solar observations at the time of launch of coronal mass ejections. Further, it is shown that in almost all major geomagnetic storms (Dst < -100 nT), the large southward magnetic fields responsible for the main phase of storms are carried by flux ropes. However, in order to predict geomagnetic storms based on the above relationships, more precise knowledge about the size and orientation of flux ropes is needed, which should be an important target of MHD simulation studies. (C) 2000 COSPAR. Published by Elsevier Science Ltd.