Alfven wave-driven solar wind during very active phases (Invited)

Abstract:

We investigate the solar wind driven by Alfven waves, particularly focusing on the solar wind during very active phases. We perform forward-type magnetohydrodynamical numerical experiments for Alfven wave-driven winds with a wide range of the input Poynting flux from the photosphere. Increasing the magnetic field strength and the turbulent velocity at the photosphere from the current averages, the mass loss rate rapidly increases at first owing to the suppression of the reflection of the Alfven waves. The surface materials are lifted up by the magnetic pressure associated with the Alfven waves, and the cool dense chromosphere is intermittently extended to 10 - 20 % of the solar radius. The dense atmospheres enhance the radiative losses and eventually most of the input Poynting energy from the solar surface escapes by the radiation. As a result, there is no more sufficient energy remained for the kinetic energy of the wind; the solar wind saturates in very active cases, as observed in solar-type stars by Wood et al. The saturation level is positively correlated with the average magnetic field strength contributed from open flux tubes. If the field strength is a few times larger than the present level, the mass loss rate could be as high as 1000 times. Some cases with large injection of Alfvenic Poynting flux show temporal inflows triggered via reflected Alfven waves at large density fluctuations. We also discuss such extreme phenomena which could occur in active phases of the Sun.