Statistical analysis of relativistic electron precipitation in the magnetosphere from POES observations

In this letter, we investigate the characters of relativistic electron precipitation (REP), which is derived from seven NOAA Polar-orbiting Operational Environmental Satellites (POES) in the time period from Jan 2012 to Dec 2017. Via an automatic algorithm, totally 62,212 REP events are identified, whose prefer regions are in the post-midnight, noon, and dawn sectors at 3.5≤L≤5.0, and pre-midnight sector at 4.5≤L≤6.0. And their occurrence rate has positive correlation with AE^* index. We suggest that REP events in the afternoon sector are associated with He⁺ band EMIC waves. According to the GEOPACK model, the field line curvature radius R_C, which is anti-correlated with AE^* index, can trigger the REP in the nightside when R_C is comparable with the gyro-radius of relativistic electron. This is also supported by observations from Cluster satellites. As a summary, our results can shed light on the fundamental characters of REP events in the magnetosphere.