Dissipation of hydromagnetic waves with application to the outer solar corona. I. Collisionless protons and collisional electrons

We discuss the theory of hydromagnetic-wave dissipation for conditions likely to occur in most of the outer solar corona (2 R0 < r <% 4 R0). Magnetoacoustic waves of period 5 min are dissipated by ion Landau damping, just as in a perfectly collisionless plasma, even though ion-electron collisions are not neglected. For certain propagation directions, dissipation by (collisional) electron thermal conduction may occur. The implications of these effects for heating the outer corona are discussed. Subject headings: corona, solar - hydromagnetics - plasmas - solar wind