Inner belt electron decay timescales: a comparison of Van Allen Probes
and DREAM3D losses following the June 2015 storm
Abstract
NASA’s Van Allen Probes observed significant, long-lived fluxes of inner
belt electrons up to ~1MeV after geomagnetic storms in
March and June 2015. Reanalysis of MagEIS data with improved background
correction showed a clearer picture of the relativistic electron
population that persisted through 2016 and into 2017 above the Fennel et
al. (2015) limit. The intensity and duration of these enhancements allow
estimation of decay timescales for comparison with simulated decay rates
and theoretical lifetimes. We compare decay timescales from these data
and DREAM3D simulations based on them using geomagnetic
activity-dependent pitch angle diffusion coefficients derived from
plasmapause-indexed wave data (Malaspina et al., 2016, 2018) and phase
space densities derived from MagEIS observations. Simulated decay rates
match observed decay rates more closely than the theoretical lifetime
due to significantly nonequilibrium pitch angle distributions in
simulation and data. We conclude that nonequilibrium effects, rather
than a missing diffusion or loss process, account for observed short
decay rates.