Nonstorm time dynamics of electron radiation belts observed by the Van Allen Probes

Storm time electron radiation belt dynamics have been widely investigated for many years. Here we present a rarely reported nonstorm time event of electron radiation belt evolution observed by the Van Allen Probes during 21–24 February 2013. Within 2 days, a new belt centering around L =5.8 formed and gradually merged with the original outer belt, with the enhancement of relativistic electron fluxes by a factor of up to 50. Strong chorus waves (with power spectral density up to 10 −4 nT 2 /Hz) occurred in the region L >5. Taking into account the local acceleration driven by these chorus waves, the two‐dimensional STEERB can approximately reproduce the observed energy spectrums at the center of the new belt. These results clearly illustrate the complexity of electron radiation belt behaviors and the importance of chorus‐driven local acceleration even during the nonstorm times.