Abstracts submitted by Bojan Vrsnak

Processes and mechanisms governing initiation and propagation of CMEs

B. Vrsnak

Hvar Observatory, Faculty of Geodesy, Zagreb, Croatia

Basic observational characteristics of CMEs (kinematics, morphology) are presented, emphasizing those aspects which are most relevant for testing physical concepts used to explain their launch and propagation. Signatures of various processes taking part during the formation of the pre-eruptive magnetic structure, its development to the acceleration stage, and the evolution in the propagation phase are described. In particular, the emerging flux process, pre-eruptive magnetic field restructuring, evolution of the eruption-associated flare and the growth of the post-eruption loop system are addressed. Special attention is paid to 3-dimensional (3-D) topology, particularly to aspects related to the concept of the semi-toroidal flux rope anchored at both ends in the inert photosphere and embedded in the coronal magnetic arcade. Basic differences between models founded on this concept and those based on 2-D or 2.5-D geometry are emphasized. In the former case the primary driver of the eruption are ideal MHD processes related to the kink instability and the torus (self-force) instability, whereas resistive processes (reconnection) take active part in driving the eruption only after the CME take-off. The role of reconnection, which takes place in the current sheet that forms below the flux rope, is essentially in supplying the "fresh" poloidal magnetic flux to the rope, thus sustaining the electric current flowing along the flux rope, and consequently, reinforcing and prolonging the CME acceleration. On the other hand, in 2-D and 2.5-D models the reconnection itself is the essential ingredient from the very beginning of the eruption, since the overlying magnetic field cannot "slip aside" the erupting structure.
Finally, eruption scenarios based on the mentioned concepts and signatures predicted by various models (analytical and numerical) are confronted with observations.