Modelling Coronal Mass Ejections -- Where Do We Stand?

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• Bernhard Kliem, University College London
• Monday 18 May 2009, 16:00-17:00
• MR14, DAMTP, Pav. F.

If you have a question about this talk, please contact Dr Geoffroy Lesur.

After a long period of considerable debate, the models of the main acceleration in coronal mass ejections (CMEs) now appear to be converging 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 already 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 magnetic arcade that extends along the polarity inversion line. I will present numerical simulations which demonstrate that the torus instability of a pre-existing flux rope explains many essential properties of CMEs in a consistent manner. The torus instability appears to be the instability connected with the well-known catastrophe mechanism of CME onset, often referred to as loss of equlibrium. On the other hand, the recent suggestion of a current channel with a hollow core (which contains the filament) represents a promising modification of the standard arcade and flux rope topologies. The physics of CME initiation and acceleration based on this topology has yet to be worked out.

Many 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 indicated 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 briefly discuss recent results of two approaches to infer the magnetic topology 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.

This talk is part of the DAMTP Astrophysics Seminars series.

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