Microbursts are pulsed precipitation events of energetic electrons from the outer radiation belt, characterized by durations less than 1s. This phenomenon is a crucial loss mechanism for energetic electrons in Earth's radiation belts and is commonly thought to be driven by whistler-mode chorus waves. A comprehensive investigation of energetic electron precipitation is of great significance for better understanding of the Earth's radiation belts dynamic and space weather forecasting. In this study, using the data from FIREBIRD-II FU3 satellite from 1 February 2015 to 7 October 2019 and FU4 satellite from 1 February 2015 to 16 March 2022, we statistically analyze the dependence of microburst events (at energies of 200 – 900 keV) on L values, MLTs, geographic distributions, and geomagnetic activity levels. The results show that microburst events mostly occurred in the outer radiation belt at the dawn side, with peak occurrence rate observed at L=6-7 and MLT=6-7. The occurrence rates of microburst events decrease with increasing electron energies, reaching approximately 3‰ for 265.4 keV electrons and 1‰ for 481.2 keV electrons. Microburst events also show a strong dependence on geomagnetic activity levels. The occurrence rate of microburst events increases with geomagnetic activity intensity. For 265.4 keV electrons, it rises from 2‰ during quiet periods to a maximum of 6‰ during active periods. The peak of occurrence rate shifts to lower L value during active periods. The global distribution characteristics of microburst occurrence rate are consistent with the amplitude distribution of whistler-mode chorus waves, indicating that the pitch angle scattering caused by chorus is an important driver of microburst. This provides key statistical observational evidence for the scattering effect of chorus waves on hundreds of keV electrons.
DownLoad: