[P-EM09] Space Weather and Space Climate

[PEM09-P15] Statistical analysis of surface charging events and their plasma environment in the medium earth orbit

*中村 雅夫¹、松井 大智¹ (1.大阪公立大学)

キーワード：宇宙機表面帯電、中高度軌道、宇宙天気

We study the surface charging events in the medium earth orbit (MEO) using the Electric Field and Wave instruments (EFW) and the Helium Oxygen Proton Electron (HOPE) data of the Van Allen Probes from 2012 to 2019. Since the Van Allen Probes are well-designed spinning scientific satellites, their severe charging events (surface charging potential < -1 kV) are only observed in the eclipse region because of the lack of the photoelectron emission. In the daylight region, however, they are shallowly charged under severe plasma environment conditions. We statistically analyze the surface charging events and the plasma environment inducing their negative potential. The results show that the surface charging events are distributed from the night side to the dawn side, and that the occurrence frequency decreases and the distribution area becomes narrower as the solar activity becomes lower. We evaluate the charging plasma environment from the electron and proton fluxes from a few eV up to 50 keV measured by the HOPE in the daylight and eclipse regions and show their statistical features and distribution in the inner magnetosphere. We will discuss the relationship between the charging environment and space weather conditions.