[P-CG21] 惑星大気圏・電磁圏

[PCG21-15] 多流体MHDシミュレーションに基づく太陽風磁場進入時の火星電離圏CO₂⁺鉛直分布にイオン種間衝突が及ぼす影響の研究

*小山 響平¹、関 華奈子²、寺田 直樹³、寺田 香織³ (1.名古屋大学大学院理学研究科、2.東京大学大学院理学研究科、3.東北大学大学院理学研究科)

キーワード：火星、電離圏、多流体MHD

The escape of the planetary atmosphere is an important phenomenon related to evolution of the atmosphere, and numerical simulations are an effective method to understand the global atmospheric escape processes. The escape of CO₂⁺ from Mars observed by Mars Express is presumed that the origin of CO₂⁺ escape flux is result of the ionospheric outflow. In this process, the escape of massive amounts of CO₂⁺ requires relatively high density of CO₂⁺ at high altitude ionosphere. Ionospheric model developed by Fox and Hac [2010] presumed chemical reaction and velocity difference for each ion fluxes in ionosphere to reproduce the density disturbance of CO₂⁺ in high altitude ionosphere. This result suggests velocity difference is important to reproduce the high CO₂⁺ density in high altitude ionosphere. Multi-fluid MHD, it is the model allows ion fluxes to take individual velocities, has developed Najib et al,. [JGR, 2011], but the model has not include the effects of the collisions between ions. In our previous research, we developed Multi-fluid MHD and reproduced Martian ionosphere. To investigate effects of collisions, we conducted 5 cases of the simulation. Case1: Multi-fluid MHD includes electron-neutral and ion-ion collisions, Case2: Multi-fluid MHD without electron-neutral collision, Case3: Multi-fluid MHD without ion-ion collisions. Case4: Multi-fluid MHD without electron-neutral and ion-ion collisions. Case5: Multi-fluid MHD. From this previous study, we obtained the effects of velocity differences between ion fluxes and collision for CO₂⁺ vertical density distribution. Our recent study is the effect of solar wind magnetic field on Martian ionosphere using under developing Multi-fluid model. Mars has no intrinsic magnetic field. So that, solar wind magnetic field penetrates into Martian ionosphere when the solar wind magnetic field is in active state. When solar wind magnetic field penetrates, Martian ionosphere is contracted, and ion-fluids are accelerated by magnetic field. Our Multi-fluid MHD code can describe individual velocity of ion fluxes, ion-ion collisions, electron-neutral collision, and effects of magnetic field for ion fluxes with different speeds. In this presentation, we report the dependence of ionospheric condition on magnetic field strength and ion velocity in the upper boundary.