EDP Sciences
Free access
Volume 446, Number 3, February II 2006
Page(s) 1139 - 1149
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20053955
A&A 446, 1139-1149 (2006)
DOI: 10.1051/0004-6361:20053955

Fast magnetoacoustic waves in curved coronal loops

I. Trapped and leaky modes
E. Verwichte, C. Foullon and V. M. Nakariakov

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 )

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-$\beta$ 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 $\alpha$. For all profiles, except for $\alpha=-4$, wave modes are not trapped in the loop and leak out into the external medium through wave tunneling.

The particular case of $\alpha=-4$, 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.

Key words: Sun: oscillations -- magnetohydrodynamics (MHD)

© ESO 2006