Wave acceleration of the fast solar wind

Abstract

Observations show that the solar wind exhibits two modes of outflow: the slow (∼400 km s −1), high density, highly variable wind that emerges from equatorial solar regions, and the high latitude, fast (∼800 km s −1), low density, steady solar wind. The bi-modal solar wind outflow is most evident near minima of solar activity. Theoretical studies of the fast solar wind in open magnetic structures motivated by SOHO, Ulysses, and Helios observations indicate that both, high frequency kinetic waves, and low frequency MHD waves play a role in its acceleration and heating. Ion-cyclotron waves have been suggested as the main energy source of the solar wind. However, there are theoretical difficulties with the ion-cyclotron wave heating of the protons, and these waves do not heat electrons. Low frequency MHD waves are still the best candidates to transport momentum and energy far from the Sun, to accelerate the solar wind on large spatial scales. I will present recently developed two-dimensional three-fluid model that includes explicit wave acceleration, and visco-resistive dissipation. The model describes electrons, protons, and minor ions as three coupled fluids that are heated by different heating processes with the parameters constrained by observations. I will present the results of 2.5D three-fluid simulations of the fast solar wind plasma that combine the effects of MHD waves self-consistently, and ion-cyclotron waves parametrically on the acceleration and heating processes. I will present the results of hybrid kinetic models of ion-cyclotron wave heating of the heavy ions in the solar wind plasma.