A three-dimensional MHD solar wind model with pickup protons

We have developed a three‐dimensional (3‐D) steady‐state MHD model of the solar corona and solar wind that covers the region from the coronal base to 100 AU and that accounts for the effects of pickup protons in the distant heliosphere. The model expands the two‐region model of Usmanov and Goldstein (2003) to include a region III that extends from 1–100 AU and incorporates a population of interstellar neutral hydrogen and its interaction with solar wind protons. Following the approach of Isenberg (1986) and Whang (1998), we consider the solar wind outside 1 AU as a combination of three comoving species, solar wind protons, electrons, and pickup protons, and solve the 3‐D steady‐state MHD equations with source terms due to photoionization and charge exchange. Separate energy equations are included for solar wind and pickup protons. We show that the pickup protons cause a deceleration of the solar wind and an increase in average plasma temperature with heliocentric distance beyond ∼10 AU. We compute the global structure of the solar wind from the coronal base to 100 AU and compare our results with Voyager 1 and 2 observations.