The damping of slow MHD waves in solar coronal magnetic fields

Abstract

A theoretical description of slow MHD wave propagation in the solar corona is presented. Two dierent damping mechanisms, namely conduction and compressive viscosity, are included and discussed in detail. We revise the proper- ties of the thermal mode, which is excited when conduction is included. The mode is purely decaying in the case of standing waves, but is oscillatory and decaying in the case of driven waves. When conduction is dominant, the waves propagate largely undamped, at the slower, isothermal sound speed. This implies that there is a minimum damping time (or length) that can be obtained by conduction alone. The results of numerical simulations are compared with TRACE observations of propagating waves, driven by boundary motions, and standing waves observed by SUMER/SOHO, excited by an initial impulse. For typical coronal conditions, conduction appears to be the dominant damping mechanism.