11:15 〜 11:30
[PCG21-08] Comparative study of two global multispecies MHD models of Mars
キーワード：火星、グローバルMHDシミュレーション、大気散逸
Escape of the ionized atmosphere to space, ion escape, has played a role in atmospheric evolution on Mars. Spacecraft observations have been conducted for decades and revealed plasma dynamics around Mars, but the global picture cannot be fully captured by only in-situ observations due to temporal and spatial limitations. Global simulation is another useful tool for studying the solar wind-Mars interactions. Numerous studies have investigated plasma phenomena in the Martian ionosphere and magnetosphere utilizing global simulations. However, there are still discrepancies not only between simulations and observations but also among simulation models. In a previous comparative study, several numerical models for Mars showed large discrepancies in plasma distributions and ion escape rates despite the same upstream inputs and the neutral atmosphere (Brain et al., 2010). The differences can arise from various factors. The extent to which physical processes, such as resistivity and photoelectron heating, are considered is a model-dependent issue. Model assumptions and numerical implementations can also influence numerical simulations.
This study aims to understand how global simulation of the solar wind-Mars interactions can differ between two global multispecies MHD models with almost the same physical and numerical implementations. The two models are the “Sun model” based on BATS-R-US (Sun et al., 2023) and the “Sakata model” based on MAESTRO (Sakata et al., in revision). Both models consider five ion species: planetary H+, O+, O2+, CO2+, and solar wind H+. We used the neutral atmosphere during the solar minimum and typical solar wind conditions, along with the same chemical reactions, collision frequencies, and inner boundary conditions. Crustal magnetic fields were not included in this study.
The baseline case shows good agreement between the models. The 1D profiles along the subsolar line look nearly identical in the shock location, the magnetic pileup, and the ionospheric composition. The escape rates of planetary ions are also in good agreement. However, there are discrepancies in the nightside ionosphere. Detailed numerical implementation can still affect the nightside and tail region representation.
In addition to the baseline case, we performed additional simulation cases to survey the effects of photoelectron heating. The simulation case with enhanced photoelectron heating shows higher plasma temperature in the ionosphere, but changes in the plasma boundaries and the ionospheric composition are negligible. The effects on the escape rates are also small except O2+. The enhancement of photoelectron heating has little effect on the global configuration of the solar wind-Mars interactions if the ionosphere is compressed and magnetized due to high solar wind dynamic pressure. In the simulation case with reduced solar wind dynamic pressure, enhanced photoelectron heating largely changes the ionosphere, the magnetic pileup, and ion escape rates. The effects of photoelectron heating may be more prominent under the solar maximum condition.
References
Brain, D., Barabash, S., Boesswetter, A., Bougher, S., Brecht, S., Chanteur, G., et al. (2010). A comparison of global models for the solar wind interaction with Mars. Icarus, 206(1), 139–151. https://doi.org/10.1016/j.icarus.2009.06.030
Sun, W., Ma, Y., Russell, C. T., Luhmann, J., Nagy, A., & Brain, D. (2023). 5-Species MHD study of Martian proton loss and source. Journal of Geophysical Research: Space Physics, 128, e2023JA031301. https://doi.org/10.1029/2023JA031301
This study aims to understand how global simulation of the solar wind-Mars interactions can differ between two global multispecies MHD models with almost the same physical and numerical implementations. The two models are the “Sun model” based on BATS-R-US (Sun et al., 2023) and the “Sakata model” based on MAESTRO (Sakata et al., in revision). Both models consider five ion species: planetary H+, O+, O2+, CO2+, and solar wind H+. We used the neutral atmosphere during the solar minimum and typical solar wind conditions, along with the same chemical reactions, collision frequencies, and inner boundary conditions. Crustal magnetic fields were not included in this study.
The baseline case shows good agreement between the models. The 1D profiles along the subsolar line look nearly identical in the shock location, the magnetic pileup, and the ionospheric composition. The escape rates of planetary ions are also in good agreement. However, there are discrepancies in the nightside ionosphere. Detailed numerical implementation can still affect the nightside and tail region representation.
In addition to the baseline case, we performed additional simulation cases to survey the effects of photoelectron heating. The simulation case with enhanced photoelectron heating shows higher plasma temperature in the ionosphere, but changes in the plasma boundaries and the ionospheric composition are negligible. The effects on the escape rates are also small except O2+. The enhancement of photoelectron heating has little effect on the global configuration of the solar wind-Mars interactions if the ionosphere is compressed and magnetized due to high solar wind dynamic pressure. In the simulation case with reduced solar wind dynamic pressure, enhanced photoelectron heating largely changes the ionosphere, the magnetic pileup, and ion escape rates. The effects of photoelectron heating may be more prominent under the solar maximum condition.
References
Brain, D., Barabash, S., Boesswetter, A., Bougher, S., Brecht, S., Chanteur, G., et al. (2010). A comparison of global models for the solar wind interaction with Mars. Icarus, 206(1), 139–151. https://doi.org/10.1016/j.icarus.2009.06.030
Sun, W., Ma, Y., Russell, C. T., Luhmann, J., Nagy, A., & Brain, D. (2023). 5-Species MHD study of Martian proton loss and source. Journal of Geophysical Research: Space Physics, 128, e2023JA031301. https://doi.org/10.1029/2023JA031301