The role of small versus large scale magnetic topologies in global waves

¹ Royal Observatory of Belgium, Brussels, Belgium
² Observatoire de Paris, CNRS, UPMC, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France e-mail: ceaulanier@wanadoo.fr

Received: 24 January 2008
Accepted: 15 July 2008

Abstract

Context. Coronal waves are large-scale structures that propagate through the lower corona over distances of hundreds of megameters. They are believed to be related to coronal mass ejections (CMEs). Attrill and collaborators suggested that the propagation of the wave front is due to consecutive reconnections in the quiet Sun of favourably orientated magnetic field lines as a magnetic flux tube expands in an active region.

Aims. I examine the validity of this mechanism describing the computed magnetic field topology underlying a coronal wave studied by Attrill and collaborators.

Methods. I perform an extrapolation of the magnetic field in and around the active region and overlay the magnetic field lines on base difference images of the coronal wave.

Results. The active region is magnetically linked to regions at a distance 300 Mm, including the northern coronal hole and the opposite hemisphere, but not to the quiet Sun surrounding the active region. The outer border of the active region is at the boundary of two different topological magnetic domains. The boundary of magnetic topological domains usually act as a barrier along which magnetic field lines can slip, but through which they cannot pass. Therefore, the quiet Sun around the active region should be barely perturbed by the motion occurring in the active region in such a pre-event magnetic field configuration.

Conclusions. In this magnetic field topology, the quiet Sun should not undergo any reconnection process due to the eruption in the active region, in contrast to the proposal of Attrill and collaborators.