Coronal mass ejections (CMEs) initiation: models and observations

We use three observed coronal mass ejection (CME) events and numerical magnetohydrodynamic simulation models to illustrate three distinct CME initiation processes: (1) streamer destabilization due to increase of currents, via increase of axial fields, of the flux-rope, (2) photospheric shear and (3) plasma flow induced CME. The 3 January 1998 event is used to illustrate the streamer destabilization process to initiate a CME because the observed height-time curve indicates that the prominence eruption proceeds the CME initiation. We interpret this CME as being initiated because of destabilization of the streamer due to the upward motion of the flux-rope by the additional Lorentz (J x B) force. On the other hand, the 22 June 1998 event shows that the CME was launched prior to the prominence eruption. This case is modeled by shear-induced loss-of-equilibrium The last case is entirely different from the previous two. The morphology of the 5 October 1996 event does not show any relation with the filament/flux-rope. We modeled this event by introducing a plasma flow. Using the observations and MHD models, we conclude that the first two categories are flux-rope driven, because the energy source, which propels the CME, is stored in the flux-rope, and the third category is driven by an assumed plasma flow with the effects of fast solar wind, because this CME appears at the boundary region of a streamer and coronal hole. (C) 2000 Elsevier Science Ltd. All rights reserved.