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 different damping mechanisms, namely thermal conduction and compressive viscosity, are included and discussed in detail. We revise the properties of the “thermal” mode, which is excited when thermal conduction is included. The thermal mode is purely decaying in the case of standing waves, but is oscillatory and decaying in the case of driven waves. When thermal 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 thermal 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, thermal conduction appears to be the dominant damping mechanism.