Rapid Enhancements of Relativistic Electrons in the Earth’s Outer
Radiation Belt caused by the Intense Substorms: A Statistical Study
Abstract
Using the data from Van Allen Probe A and B, we investigate rapid
enhancements of relativistic electrons in the Earth’s outer radiation
belt caused by the intense substorms (AEmax
> ~ 900 nT) for 29 events from January 2013
to April 2015. These intense substorms may occur during the storm main
phase or recovery phase. Based on the different substorm evolution
characteristics, the intense substorms are divided into isolated
substorm activities and continuous substorm activities. In this study,
we set a criterion for rapid enhancements when the electron phase space
densities (PSDs) for μ = 1096, 2290, and 3311 MeV/G increased by
more than 2 times in 9 hours. In the time interval of 9 hours, the local
acceleration of chorus waves is the dominant process for accelerating
the seed populations (100s keV) up to MeV energies. Our statistical
results show that enhanced chorus waves and seed electrons during the
intense substorms are observed in the outer radiation belt. Continuous
substorm activities can more rapidly (< 9 h) and efficiently
accelerate relativistic electrons in the outer radiation belt than
isolated substorm activity. During the intense substorms, MeV electron
injections could contribute to rapid enhancements of relativistic
electrons in the outer radiation belt. Our statistical study suggests
that the intense substorms during geomagnetic storms have a significant
effect on the rapid variations of relativistic electron dynamics.