The effect of the solar wind on CME triggering by magnetic foot point shearing

Centrum voor Plasma-Astrofysica, Celestijnenlaan 200B, 3001 Leuven, Belgium e-mail: Carla.Jacobs@wis.kuleuven.be

Received: 9 December 2005
Accepted: 11 January 2006

Abstract

Context.Photospheric motions and a sheared configuration of the magnetic field are often considered as precursors of violent solar phenomena such as flares and Coronal Mass Ejections (CMEs). Therefore, in many numerical CME initiation studies shearing of the magnetic foot points is used as a mechanism to make the magnetic field unstable and to trigger the CME event.

Aims.From that point of view we decided to do a parameter study that investigates the effect of the different initiation parameters, in particular the effect of the shear flow velocity. Moreover, the simulations were performed on three different background solar wind models. In this way, both effects of the background wind and the initiation parameters on the CME evolution are quantified.

Methods.The results are obtained by means of a finite volume, explicit solver to advance the equations of ideal magnetohydrodynamics. All simulations involve the same numerical grid, the same numerical technique and similar boundary conditions, so that the results can be compared in an unequivocal way.

Results.The foot points of the magnetic field lines are sheared by introducing an extra longitudinal flow profile on the solar surface with a maximum velocity ranging from 3 km s^-1 to 9 km s^-1. The temporal evolution of the magnetic energy, the velocity of the flux rope, and the magnetic helicity show a dependence on the maximum shear velocity as well as on the background wind model.