Rapid Relativistic Electron Enhancements and Associated Particle Injections: A Multi-Spacecraft Statistical Study

Rapid relativistic electron enhancements (REE) in the outer radiation belt have long been an intriguing phenomenon for space weather. In this study, we investigate rapid REE from October 2012 to December 2017 using multi-spacecraft observations. A total of 27 rapid REE events are identified from the Van Allen Probes (RBSP) measurements with a 5 times increase of MeV electrons at the center of the outer radiation belt (L = 4.5-5.5) in a half RBSP orbit (similar to 4.5 hr). All REE events are found to be in association with pulse-like injections of MeV electrons in the outer radiation belt. Electron fluxes in each injection at L similar to 6.6 and the overall electron enhancements at L = 4.5-5.5 are quantified. The 500 keV and 0.8-1 MeV electron fluxes are correlated in injections and in overall enhancements. Substorm strength is more intense before/during the REE than intervals after the REE. The statistical study suggests that substorm-associated MeV electron injections are highly correlated with rapid REE in the outer radiation belt. Rapid relativistic electron enhancements (REE) in the outer radiation belt are one of the most important phenomena in space weather. The fast increases of MeV energy electrons can have significant impacts on satellite operations and safety. In this study, we identify 27 events of relativistic electron enhancements in which MeV electron increases five times in similar to 4.5 hr at a radial distance of 4.5-5.5 Earth radius. All REE events are found in association with multiple pulse-like injections of MeV electrons. The electron fluxes during each injection at geosynchronous altitude and the overall enhancements in the center of the radiation belt are quantified. The increases in sub-relativistic and MeV electron fluxes are highly correlated. Overall, this research provides insights into the correlation between substorm-associated MeV electron injections and the rapid intense REE in the outer radiation belt, contributing to a better understanding of the dynamics and processes involved in the radiation belt particle energization. All 27 events of rapid enhancement of relativistic electrons are found to be associated with injections of MeV electronsThe 500 keV and 0.8-1 MeV electron fluxes are highly correlated during injections at L similar to 6.6 and in overall enhancements at L = 4.5-5.5Substorm strength is more intense during rapid relativistic electron enhancements