Three-dimensional MHD Modeling of the Solar Wind with Pickup Ions

Using a 3D MHD steady-state solar wind model we have simulated the magnetic field and plasma distribution throughout the heliosphere from the coronal base out to 100~AU for a dipole magnetic field on the Sun tilted by 30° to the solar rotation axis. This represents the solar conditions typical for a declining phase of solar cycle. The model assumes a uniform distribution of neutral hydrogen throughout the heliosphere and accounts for the processes of photoionization and charge exchange between the solar wind protons and pickup protons. We present simulation results on the formation of corotating interaction regions, their evolution with heliocentric distance, and the effects of pickup protons in this evolution. The simulation results are consistent with earlier studies in showing that the pickup protons cause a deceleration of the solar wind beyond 10~AU. Comparison of simulation runs with and without pickup protons shows that the pickup protons act to weaken the corotating interaction regions. This is presumably due to the deceleration of solar wind and additional pressure from the pickup protons. The results show a significant latitude-dependent compression effect of the deceleration on the interplanetary magnetic field. The proposed solar wind model can be useful in studies of the global heliospheric structure and the interaction of solar wind with the LISM.