Solar Wind—Venus Interaction During the Solar Maximum and Solar Minimum Periods: A Newly Developed Multi-Fluid MHD Model

To investigate the individual behavior of ion species, a three-dimensional multi-fluid magnetohydrodynamic model was developed to simulate the global interaction between the solar wind and Venus under different solar conditions. The model includes H⁺, O₂⁺, O⁺, and CO₂⁺, resolving their continuity, momentum, and energy conservation for plasma flow. The differences between the solar maximum and minimum cases are reflected in the variations of solar EUV flux, solar wind dynamic pressure, and corresponding changes in atmospheric distributions. Simulation results show that the bow shock shifts inward during the solar minimum. The model incorporates motional, Hall, and ambipolar electric fields. The results reveal that the electron pressure gradient force acts to decelerate the solar wind at the bow shock. During solar minimum, enhanced solar wind dynamic pressure steepens the electron pressure gradient at the bow shock, strengthening the outward electron pressure gradient force, which counteracts the solar wind more efficiently at a distance closer to Venus. Additionally, during solar minimum, increased transport of O⁺ and CO₂⁺ from the dayside to the magnetotail leads to a higher ion escape rate, consistent with enhanced solar wind energy transfer. In contrast, O₂⁺ exhibits greater transport to the nightside during solar maximum due to its distinct production mechanism, which relies on ion-neutral reactions rather than direct photoionization. These findings highlight that this model could serve as an efficient tool for studying ion-scale processes and may have applications in investigating the impact of individual upstream conditions on the induced magnetic field and ion dynamics.