On the Dynamics of Ultrarelativistic Electrons (>2 MeV) Near L* = 3.5 During 8 June 2015

Abstract

Understanding local loss processes in Earth’s radiation belts is critical to understanding their overall structure. Electromagnetic ion cyclotron waves can cause rapid loss of multi‐MeV electrons in the radiation belts. These loss effects have been observed at a range of L* values, recently as low as L* = 3.5. Here, we present a case study of an event where a local minimum develops in multi‐MeV electron phase space density (PSD) near L* = 3.5 and evaluate the possibility of electromagnetic ion cyclotron (EMIC) waves in contributing to the observed loss feature. Signatures of EMIC waves are shown including rapid local loss and pitch angle bite outs. Analysis of the wave power spectral density during the event shows EMIC wave occurrence at higher L* values. Using representative wave parameters, we calculate minimum resonant energies, diffusion coefficients, and simulate the evolution of electron PSD during this event. From these results, we find that O+ band EMIC waves could be contributing to the local loss feature during this event. O+ band EMIC waves are uncommon, but do occur in these L* ranges, and therefore may be a significant driver of radiation belt dynamics under certain preconditioning of the radiation belts.