[P-CG19] Planetary Magnetosphere, Ionosphere, and Atmosphere

[PCG19-P02] Ion density variations in the Martian upper atmosphere during dust storms observed by MAVEN/STATIC

*Taiga Osanai¹, Kei Masunaga², Naoki Terada¹, Nao Yoshida¹, Takuya Hara³, Shotaro Sakai¹ (1.Graduate School of Science, Tohoku University, 2.Institute of Space and Astronautical Science ,Japan Aerospace Exploration Agency, 3.Space Sciences Laboratory, University of California, Berkeley)

Keywords:Mars, Dust Storm, MAVEN, Martian upper ion

Due to no intrinsic magnetic fields on Mars, a state of Martian upper atmosphere is highly controlled by the solar wind and solar flux. However, recent studies showed that the amount of various atmospheric components in the Martian thermosphere and exosphere fluctuates in response to Martian dust storms (e.g., Yoshida et al., 2021). Recently, HISAKI space telescope observations during a major dust storm period have shown that the total amount of hydrogen and oxygen atoms in the upper atmosphere varies periodically, likely imposed by the atmospheric waves in the lower atmosphere (Masunaga et al., submitted). However, it is unclear how the variations of thermospheric and exospheric abundances affect ion abundances in the upper atmosphere during dust storms.
Using the SupraThermal And Thermal Ion Composition (STATIC) on the MAVEN spacecraft, we analyzed the variation of the number density of five ion species (H⁺,He⁺⁺,O⁺,O₂⁺,CO₂⁺) observed, during a major dust storm that occurred in September 2016. In order to access the solar wind and lower atmospheric effects on the ionosphere and upper regions, we grouped the observed data into four plasma regions: the solar wind, the magnetosheath, the magnetic pileup region, and the ionosphere. We then analyzed the mean number density variation per orbit in each region. Since the ionization rates are dependent on the solar flux, each plasma region is further divided into the sunlit and shadow regions
We found that show characteristic periodic variations in the ionosphere (150-250 km), and that O₂⁺,CO₂⁺ increase by a factor of 10 as the day passes in the ionosphere. In particular, number density varied with a periodicity different from that of high-altitude regions such as the solar wind and magnetic sheath, which suggests that the ionospheric ions are influenced by the lower atmospheric effects due to dust storms. In this presentation, we will compare and discuss the periodic density variations of H⁺ and O⁺ in the ionosphere observed by STATIC and those of H and O in the thermosphere found in previous studies.