The Regular Features Recorded by the Langmuir Probe Onboard the Low Earth Polar Orbit Satellite CSES

This paper presents two kinds of regular features revealed from the observations of the Langmuir probe (LAP) onboard the low-earth polar orbit satellite - China Seismo-Electromagnetic Satellite (CSES). The first feature behaves as a sudden drop (SD) in the plasma potential (Vp) and floating potential (Vf) data, while the second one appears as a spike (SP) in the dayside Vp and Vf data. The SD structure occurs at geo-latitudes from 40 degrees N to 65 degrees N, roughly from mid-March to mid-September months but with an apparent yearly growth of its amplitude. The SD is caused by the satellite-current system adjustment at the terminator transition zone. The SP feature predominately appears at geo-latitudes from 10 degrees S to 40 degrees N, showing annual recurrence and growing amplitude. Simulation suggests that the SP is caused by instantaneous illumination changes of probe surface when the boom of the electric field detector in the windward panel shades the LAP. According to the analysis of I-V curves both inside and outside the SD and SP structures, we exclude the possibility of probe contamination and confirm that the scientific data of CSES LAP are reliable. These two regular features depend on the solar illumination conditions and the corresponding adjustment of the satellite-current system equilibrium. This study provides a valuable reference for validating and pre-calibrating data from LAP in-situ measurements onboard similar low-earth polar orbit satellites.