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

Abstract

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.

Time‐Dependent Inversion of Energetic Electron Precipitation Spectra From Ground‐Based Incoherent Scatter Radar Measurements

“…Moreover, the conjunction presented in Figure 1a is not perfect, it could also be the case that the radar did not encounter the precipitation patch observed by the spacecraft simply due to spatial separation between the spacecraft and the radar footprints. Similar situations have been encountered by other authors (e.g., Sanchez et al., 2022) that have argued that the precipitation structures may be spatially smaller than the distance between the instrument footpoints.…”

“…(Sivadas et al, 2017) used Poker Flat Incoherent Scatter Radar (PFISR), Time History of Events and Macroscale Interactions during Substorm (THEMIS) spacecraft, all sky cameras and an inversion technique to constrain the source location and acceleration mechanism of precipitating electrons of different energy ranges. Sanchez et al (2022) have used Van Allen Probes-PFISR conjunctions to compare ionization altitude profiles expected in the atmosphere due to energetic electron precipitation and the ionization profiles measured with ISRs. In Kaeppler et al (2020), two conjunction observations between the Van Allen Probes and the PFISR were studied, one for a quiet-time event and the other for a storm-time event, for which the foot-points of RBSP were within 500 km from PFISR.…”

“…It illustrates the difficulties encountered when comparing precipitation observed by space platforms and the expected associated enhancements in observed electron density by ground radar. In order to allow for the exploration of a wide range of possibilities in scale size of precipitating regions, a conjunction was defined when the spacecraft's magnetic footpoint at ∼75 km altitude passes within a few hundred km of PFISR's footpoint (e.g., Nishimura et al., 2011; Sanchez et al., 2022). This is applicable to the case presented in this section as well as the inversion case presented in Section 3.1.…”

“…Sanchez et al. (2022) have used Van Allen Probes‐PFISR conjunctions to compare ionization altitude profiles expected in the atmosphere due to energetic electron precipitation and the ionization profiles measured with ISRs. In Kaeppler et al.…”

Analysis of Electron Precipitation and Ionospheric Density Enhancements Due To Hiss Using Incoherent Scatter Radar and Arase Observations

“…Above ∼90 km altitude, frequency aliasing prevents estimation of the spectrum using pulse-to-pulse processing, although the total scattered power can still be measured. Further details of this mode are described in Sanchez et al (2022).…”