The damping of slow MHD waves in solar coronal magnetic fields

II. The effect of gravitational stratification and field line divergence

School of Mathematics and Statistics, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, Scotland, UK

Corresponding author: I. De Moortel, ineke@mcs.st-and.ac.uk

Received: 27 August 2003
Accepted: 12 November 2003

Abstract

This paper continues the study of De Moortel & Hood ([CITE]) into the propagation of slow MHD waves in the solar corona. Firstly, the damping due to optically thin radiation is investigated and compared to the effect of thermal conduction. In a second stage, gravitational stratification is included in the model and it is found that this increases the damping length significantly. Finally, the effect of different magnetic field geometries on the damping of the slow waves is investigated. As a first approximation, a purely radial magnetic field is considered and although the amplitudes of the perturbations decrease due to the divergence of the field, the effect is small compared to the effect of thermal conduction. A more realistic local geometry, estimated from the observations, is investigated and it is demonstrated that a general area divergence can cause a significant, additional, decrease of the amplitudes of the perturbations. The results of numerical simulations, incorporating the effects of gravitational stratification, the magnetic field geometry and thermal conduction are compared with TRACE observations of propagating waves in coronal loops. It is found that a combination of thermal conduction and (general) area divergence yields detection lengths that are in good agreement with observed values.