Resonance absorption of compressible magnetohydrodynamic waves at thin 'surfaces'

The behavior of plasma and fields in the transition layer supporting MHD surface waves is analyzed, assuming that the total pressure fluctuations, delta-P(tot), can be taken to be nearly constant across this thin transition layer, with a value nearly the same as would be obtained if the MHD wave were supported by a truly discontinuous surface. Regarding therefore delta-P(tot) as known, the plasma and field equations in the transition layer were cast into a form in which delta-P(tot) appeared as a driving term. Among the two resonances that appear (the cusp resonance and the Alfven resonance) special attention is given to the Alfven resonance, which affects the velocity and magnetic field components normal to the background magnetic field. The effects of three types of viscosity on the Alfven resonance are considered, and it is shown that energy is pumped out of the surface wave into thin layers surrounding the resonant field lines.