Fast magnetoacoustic waves in curved coronal loops

I. Trapped and leaky modes

Department of Physics, University of Warwick, Coventry CV4 7AL, UK e-mail: Erwin.Verwichte@warwick.ac.uk

Received: 1 August 2005
Accepted: 15 September 2005

Abstract

A study of vertically polarised fast magnetoacoustic waves in a curved coronal loop is presented. The loop is modeled as a semi-circular magnetic slab in the zero plasma-β limit. The governing equations for linear waves are derived. We show that the wave mode behaviour depends on the slope of the equilibrium density profile, which is modeled as a piece-wise continuous power law curve of index α. For all profiles, except for , wave modes are not trapped in the loop and leak out into the external medium through wave tunneling. 
The particular case of , which corresponds to a linearly increasing Alfvén speed profile, is examined in more detail as this is the only model that can support trapped wave modes. We compare the results with a straight slab model and find similar behaviour. Coupling between sausage and kink wave modes has not been found in the model.