[P-EM11] Space Weather and Space Climate

[PEM11-P10] Statistical analysis of plasma energy flux distribution for spacecraft surface charging in the inner magnetosphere

*Masao Nakamura¹, Daichi Matsui¹ (1.Osaka Metropolitan University)

Keywords:Spacecraft surface charging, Inner magnetosphere, Space weather

Spacecraft surface charging is induced by the interaction of ambient plasma with the spacecraft surface and sometimes causes spacecraft anomalies due to electrostatic discharging (ESD) in the inner magnetosphere. We have studied surface charging events using data from the Electric Field and Wave (EFW) instruments and the Helium Oxygen Proton Electron (HOPE) sensors on the Van Allen Probes from 2012 to 2019. The results show that the surface charging events are distributed from the night side to the dawn side and the occurrence frequency of these events depends on solar activity. We statistically analyzed the plasma environment with a superposed analysis of the plasma energy flux distribution in the daylight region from the night side to the dawn side. The analysis reveals that a necessary condition for the negative surface charging is that the integral flux of high-energy (> 8 keV) electrons exceeds a threshold value and the total electron current is larger than the photoelectron current. A sufficient condition for the negative surface charging is that the low-energy electron flux is smaller than the flux observed during charging events because the current of secondary electrons generated by these low-energy electrons is smaller than the sum of all other currents. We will discuss the relationship between these charging conditions and space weather conditions.