Reflection of Alfvén Waves and Heating in Solar Coronal Holes

Abstract

Using a simple model coronal hole, we estimate the short-period period limit for the reflection of Alfven waves in solar coronal holes. Waves with periods longer than this limit are strongly reflected and blocked from escaping into the solar wind; waves with periods appreciably shorter than this limit suffer little reflection and freely escape into the solar wind. For temperature, density, and strength and fanning out of the magnetic field all representative of real coronal holes, we find that the value of this limiting period and its dependence on temperature and field spreading encourage the view of Hollweg (1981, 1986) and Parker (1987, 1988) that coronal holes are heated by Alfven waves.