A three-dimensional MHD solar wind model with pickup protons

Abstract

We have developed a three-dimensional (3-D) steady-state MHD model of the solarcorona and solar wind that covers the region from the coronal base to 100 AU and thataccounts for the effects of pickup protons in the distant heliosphere. The model expandsthe two-region model of Usmanov and Goldstein (2003) to include a region III thatextends from 1–100 AU and incorporates a population of interstellar neutral hydrogen andits interaction with solar wind protons. Following the approach of Isenberg (1986) andWhang (1998), we consider the solar wind outside 1 AU as a combination of threecomoving species, solar wind protons, electrons, and pickup protons, and solve the 3-Dsteady-state MHD equations with source terms due to photoionization and chargeexchange. Separate energy equations are included for solar wind and pickup protons. Weshow that the pickup protons cause a deceleration of the solar wind and an increase inaverage plasma temperature with heliocentric distance beyond 10 AU. We compute theglobal structure of the solar wind from the coronal base to 100 AU and compare ourresults with Voyager 1 and 2 observations.