[P-CG21] Planetary Magnetosphere, Ionosphere, and Atmosphere

[PCG21-P06] Statistical study of Martian nightside ionosphere dependences on the solar wind condition, IMF clock angle, and the crustal magnetic field on Mars

*Naoyuki Takeuchi¹, Yuki Harada¹ (1.Graduate School of Science, Kyoto University)

Keywords:Mars, Nightside ionosphere, Solar wind, Interplanetary magnetic field, Crustal magnetic field

Despite the lack of solar radiation, on the nightside of Mars exists the tenuous and variable ionosphere. This Martian nightside ionosphere is thought to have two dominant sources: Electron Impact Ionization (EII) and day-to-night plasma transport. The former is caused by the solar wind electron precipitation and the drivers of the latter include the pressure gradient. These sources are affected by solar wind conditions, IMF clock angle, and the strong crustal magnetic field, which is located in the southern hemisphere of Mars, and the dependences of the nightside ionosphere are studied by Diéval et al. (2014). However, the time and spatial coverage of this previous study were not enough because they analyzed only six months of data. In addition, large uncertainties existed in the solar wind conditions and IMF clock angle inferred from the MGS proxy data.
In this research, we perform statistical research over a much longer period from November 2014 to September 2023, using the data obtained by Mars Express (MEX) observing the nightside ionosphere by remote sensing and Mars Atmosphere and volatile EvolutioN (MAVEN) observing solar wind conditions and IMF clock angle in situ. We re-investigate the dependences of the Martian nightside ionosphere on solar wind conditions, IMF clock angle, and the crustal magnetic fields. The larger volume of data enables us to ensure more complete time and spatial coverages, and direct measurements of the solar wind and IMF improve the accuracy of the upstream information. We also discuss our results in comparison to recent studies of the Martian discrete aurora.