Wave Heating and Acceleration of the Fast Solar Wind

Abstract

Wave heating and acceleration of the fast solar wind has been studied and debated for decades. Low frequency MHD waves, and high frequency ion-cyclotron waves were proposed separately as the sources of energy and momentum of the solar wind. Recent UVCS observations and theoretical studies suggest that the resonant absorption of ion cyclotron waves heats and accelerates the minor ions in the solar corona. Velocity distributions of minor ions derived from SOHO UVCS observations in coronal holes indicate that the minor ion temperature anisotropy is > 10 and the outflow speeds of minor ions are higher then those of the solar wind protons. However, the evidence for ioncyclotron heating of protons is not as strong. The formation of fast solar wind requires the transfer of energy and momentum to several solar radii into the corona. This can not be achieved solely by ion-cyclotron waves that form in the magnetic network low in the corona, but can be done by low-frequency MHD waves. In view of recent observations and models, I will discuss the combined low-frequency and high-frequency wave heating and accelerations of the fast solar wind. I will present the results of 2.5D MHD, 3-fluid, and hybrid models of the acceleration of the fast solar wind by low-frequency and high frequency Alfven waves.