VISCOUS MAGNETOHYDRODYNAMIC MODES AND P-MODE ABSORPTION BY SUNSPOTS

We discuss several features of viscous compressible magnetohydrodynamic (MHD) modes in a uniformly magnetized medium and viscous MHD mode conversion in the presence of background inhomogeneity. For the static background equilibrium in which physical quantities vary continuously, the well-known singularities for ideal MHD perturbations are removed by viscosity, and in their places the viscous MHD resonance layers appear. It is shown that in the presence of the viscous MHD resonance layers, viscous MHD mode conversion can be very effective in absorbing the power of an incident acoustic wave upon an isolated, inhomogeneously magnetized flux tube. Based on this, we suggest a possible interpretation for the reported p-mode absorption by sunspots embedded in the solar photosphere.