Coronal heating by Alfven waves

Abstract

Coronal heating by Alfven waves is reexamined considering the effect of the the granular structure of the sun's surface. From the observation that the Alfven waves in the sun's atmosphere are originally generated by the surface granular motion, it is speculated that the coronal Alfven waves may possess the intrinsic transversal length scale of the granular size from the time of their generation. Thus, the dispersion relation for Alfven waves with a transversal variation has been calculated, incorporating Braginskii's expression of viscosity. As a result, it is found that there is a branch of Alfven waves which can be effectively damped by the viscosity, in addition to the branch of Alfven waves which are not damped. The short transversal length scale associated with the granular cells seems to have the potential to damp the Alfven waves effectively in the corona.