Penetration of MeV electrons into the mesosphere accompanying pulsating aurorae

A Test of Energetic Particle Precipitation Models Using Simultaneous Incoherent Scatter Radar and Van Allen Probes Observations

Quantification of energetic electron precipitation caused by wave-particle interactions is fundamentally important to understand the cycle of particle energization and loss of the radiation belts. One important way to determine how well the wave-particle interaction models predict losses through pitch-angle scattering into the atmospheric loss cone is the direct comparison between the ionization altitude profiles expected in the atmosphere due to the precipitating fluxes and the ionization profiles actually measured with incoherent scatter radars. This paper reports such a comparison using a forward propagation of loss-cone electron fluxes, calculated with the electron pitch angle diffusion model applied to Van Allen Probes measurements, coupled with the Boulder Electron Radiation to Ionization model, which propagates the fluxes into the atmosphere. The density profiles measured with the Poker Flat Incoherent Scatter Radar operating in modes especially designed to optimize measurements in the D-region, show multiple instances of close quantitative agreement with predicted density profiles from precipitation of electrons caused by wave-particle interactions in the inner magnetosphere, alternated with intervals with large differences between observations and predictions. Several-minute long intervals of close prediction-observation approximation in the 65-93 km altitude range indicate that the whistler wave-electron interactions models are realistic and produce precipitation fluxes of electrons with energies between 10 keV and >100 keV that are consistent with observations. The alternation of close model-data agreement and poor agreement intervals indicates that the regions causing energetic electron precipitation are highly spatially localized.