Damping of Longitudinal MagnetoAcoustic Oscillations in Slowly Varying Coronal Plasma
Abstract
We investigate the propagation of MHD waves in a magnetised plasma in a weakly stratified atmosphere, representative of hot coronal loops. In most earlier studies, a timeindependent equilibrium was considered. Here we abandon this restriction and allow the equilibrium to develop as a function of time. In particular, the background plasma is assumed to be cooling due to thermal conduction. The cooling is assumed to occur on a time scale greater than the characteristic travel times of the perturbations. We investigate the influence of cooling of the background plasma on the properties of magnetoacoustic waves. The MHD equations are reduced to a 1D system modelling magnetoacoustic modes propagating along a dynamically cooling coronal loop. A timedependent dispersion relation that describes the propagation of the magnetoacoustic waves is derived using the WKB theory. An analytic solution for the timedependent amplitude of waves is obtained, and the method of characteristics is used to find an approximate analytical solution. Numerical calculations of the analytically derived solutions are obtained to give further insight into the behaviour of the MHD waves in a system with a variable, timedependent background. The results show that there is a strong damping of MHD waves and the damping also appears to be independent of the position along the loop. Studies of MHD wave behaviour in a timedependent backgrounds seem to be a fundamental and very important next step in the development of MHD wave theory that is applicable to a wide range of situations in solar physics.
 Publication:

Solar Physics
 Pub Date:
 August 2011
 DOI:
 10.1007/s1120701197955
 arXiv:
 arXiv:1011.2617
 Bibcode:
 2011SoPh..272...73E
 Keywords:

 Magnetohydrodynamics (MHD);
 Plasmas;
 Sun: corona;
 Waves;
 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 14 pages