[P-EM12] Coupling Processes in the Atmosphere-Ionosphere System

[PEM12-10] Identifying atmospheric waves and solar wind impacts in the Martian thermosphere and ionosphere

*Hiromu Nakagawa¹, Scott England², Nao Yoshida¹, Shotaro Sakai¹, Yuki Harada³, Naoki Terada¹, Kaori Terada¹, Kanako Seki⁴, Hitoshi Fujiwara⁵, Takeshi Imamura⁶ (1.Graduate School of Science, Tohoku University, 2.Aerospace and Ocean Engineering, Virginia Polytechnic Institute and State University, 3.Graduate School of Science, Kyoto University, 4.Graduate School of Science, University of Tokyo, 5.Education and Research center for sustainable development, Faculty of Science and Technology, Seikei University, 6.Graduate School of Frontier Sciences, University of Tokyo)

Keywords:Mars, atmospheric wave, solar wind, thermosphere, ionosphere

Wave-like density perturbations are ubiquitously found in the ions and neutrals in the Martian thermosphere and ionosphere. The excitation mechanism of these wave-like perturbations is still an open question. In order to identify atmospheric waves propagating from below and solar wind impacts from above in the Martian thermosphere and ionosphere, we extract the perturbation components in neutral and ion density profiles obtained from in-situ observations by NGIMS onboard MAVEN for five years from 2015 to 2020 at altitude range between 170 and 210 km. We focus on wave coupling between neutral-neutral (CO2-N2) and ion-neutral (O2+-CO2) species.
We found a great agreement with atmospheric gravity waves for the neutral-neutral coupling at the low altitudes (170-190 km). This agreement decreases at higher altitudes (190-210 km). The ion perturbations follow the neutral perturbations – a sign of ion-neutral coupling, which can be almost explained by the atmospheric gravity waves but not as good as the neutral-neutral coupling. The ion-neutral coupling gets lower at higher altitudes. This feature can be found in both day and night side. For the extreme solar wind events with coronal mass ejections, we got essentially the same result in the neutral coupling as we had in the quiet cases. The big difference is the abrupt drop in the ion-neutral coupling. That is consistent with a strong disruption related to solar wind electric field on ions. The ions move independent of the neutrals, do not reflect the atmospheric gravity waves. Ion-specific features are significant especially in the nightside and at higher altitudes. In at least some cases, the transition is consistent with the increasing gyro/collision frequency ratio. It is noteworthy that a small fraction of the neutral-neutral coupling could be explained by the acoustic waves, and none of the ion-neutral coupling by the acoustic waves.