Differentiating Between Simultaneous Loss Drivers in Earth’s Outer
Radiation Belt: Multi Dimensional Phase Space Density Analysis
Abstract
We analyzed the contribution of electromagnetic ion cyclotron (EMIC)
wave driven electron loss to a flux dropout event in September 2017. The
evolution of electron phase space density (PSD) through the dropout
showed the formation of a radially peaked PSD profile as electrons were
lost at high L*, resembling distributions created by magnetopause
shadowing. By comparing 2D Fokker Planck simulations of pitch angle
diffusion to the observed change in PSD, we found that the μ and K of
electron loss aligned with maximum scattering rates at dropout onset. We
conclude that, during this dropout event, EMIC waves produced
substantial electron loss. Because pitch angle diffusion occurred on
closed drift paths near the last closed drift shell, no radial PSD
minimum was observed. Therefore, the radial PSD gradients resembled
solely magnetopause shadowing loss, even though the local pitch angle
scattering produced electron losses of several orders of magnitude of
the PSD.