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SUMMARY:Modelling Coronal Mass Ejections -- Where Do We Stand? - Bernhard 
 Kliem\, University College London
DTSTART:20090518T150000Z
DTEND:20090518T160000Z
UID:TALK17137@talks.cam.ac.uk
CONTACT:Dr Geoffroy Lesur
DESCRIPTION:After a long period of considerable debate\, the models of the
  main acceleration in coronal mass ejections (CMEs) now appear to be conve
 rging toward a major role being played by a magnetic flux rope\, suspended
  in the corona above a polarity inversion line of the photospheric field. 
 The models differ primarily in supposing either that the flux rope is alre
 ady present at the onset of the main acceleration or that it is formed in 
 the course of the acceleration by magnetic reconnection in the core of a m
 agnetic arcade that extends along the polarity inversion line. I will pres
 ent numerical simulations which demonstrate that the torus instability of 
 a pre-existing flux rope explains many essential properties of CMEs in a c
 onsistent manner. The torus instability appears to be the instability conn
 ected with the well-known catastrophe mechanism of CME onset\, often refer
 red to as loss of equlibrium. On the other hand\, the recent suggestion of
  a current channel with a hollow core (which contains the\nfilament) repre
 sents a promising modification of the standard arcade and flux rope topolo
 gies. The physics of CME initiation and acceleration based on this topolog
 y has yet to be worked out.\n\nMany if not all CMEs exhibit an activation 
 phase\, also known as slow-rise phase of the filament\, which precedes the
  onset of the main acceleration. Recent observations have clearly indicate
 d that this phase is distinct from the main acceleration. However\, there 
 is no physical model yet that describes this phase and its onset. I will b
 riefly discuss recent results of two approaches to infer the magnetic topo
 logy in this phase: X-ray sigmoid observations and simulations of the CME-
 flare relationship. Both support the flux rope topology but differ in the 
 implication for the presence of a magnetic X line.
LOCATION:MR14\, DAMTP\, Pav. F
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