On the dynamics of ultra-relativistic 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 and contribute to an uncommon three-belt structure 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 near L* = 3.5 and evaluate the possibility of 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 event shows EMIC wave
occurrence at higher L* values. Using these 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.