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 (AE ma x > ∼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 non‐continuous intense substorm activities and continuous intense substorm activities. In this study, we set a criterion for rapid enhancements when the electron phase space densities for μ = 1,096, 2,290, and 3,311 MeV/G increased by more than two times in 9 hr. In the time interval of 9 hr, the local acceleration by chorus waves is the dominant process for accelerating the seed populations (hundred kiloelectron volts) 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 intense substorm activities can more rapidly (<9 hr) and efficiently accelerate relativistic electrons in the outer radiation belt than non‐continuous intense substorm activities. During the intense substorms, the electric field acceleration 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.