Parametric Sensitivity of the Formation of Reversed Electron Energy Spectrum Caused by Plasmaspheric Hiss

Abstract

Scattering by plasmaspheric hiss is responsible for the newly reported reversed energy spectra with abundant high‐energy but fewer low‐energy electrons between hundreds of kiloelectronvolts and ~2 MeV in the inner magnetosphere. To deepen our understanding of the contributions of plasmaspheric hiss to the formation of reversed electron energy spectrum, we conduct a detailed theoretical parametric analysis through numerical simulations to explore the sensitivity of hiss‐induced reversed electron energy spectrum to ambient magnetic field, plasma density, and hiss wave distribution properties. Given L‐shell, variations of ambient plasma density and wave frequency spectrum contribute importantly to the formation of reversed electron energy spectrum, while variations of background magnetic field (which usually shows small changes in the plasmasphere) and wave normal angle distribution play a less effective role. Our study suggests that the reversed electron energy spectrum has important implications for unveiling the sophisticated energy‐dependent nature of wave‐particle interactions and energetic particle dynamics in geospace.

A Short‐lived Three‐Belt Structure for sub‐MeV Electrons in the Van Allen Belts: Time Scale and Energy Dependence

“…BOT distributions have been proven to be a consequence of particles' loss to atmosphere driven by hiss wave scattering (Ni et al, 2019; Zhao, Johnston, et al, 2019; Zhao, Ni, et al, 2019). Zhao, Johnston, et al (2019) and Ni et al (2019) suggested that interaction with hiss waves inside the plasmapause could effectively scatter electrons with the energy of hundreds keV to the loss cone, which results in the BOT distributions. Statistical results by Zhao, Johnston, et al (2019) indicated that the BOT spectra are confined inside the plasmapause and take ∼1–2 days to form.…”

Combined Scattering of Radiation Belt Electrons Caused by Landau and Bounce Resonant Interactions With Magnetosonic Waves

“…Several plasma wave modes observed in the inner magnetosphere are believed to contribute to resonant scattering of radiation belt electrons. For instance, chorus waves are regarded as an important mechanism to accelerate radiation belt electrons (e.g., Millan & Baker, ), while chorus, electromagnetic ion cyclotron waves, and plasmaspheric hiss can lead to the losses of radiation belt electrons (e.g., Millan & Thorne, ; Ni et al, , , ; Zhao et al, ). However, most of those studies have focused on the cyclotron resonance which can violate the first adiabatic invariant.…”

An empirical model of the global distribution of plasmaspheric hiss based on Van Allen Probes EMFISIS measurements

“…In summary, it is well demonstrated, by quantitative comparisons between the statistical observations and model results, that the empirical model in terms of fitted functions can reflect favorably the major features of the global distribution of hiss wave intensity, including the MLT asymmetry, substorm dependence, and latitudinal variations (Xiang Z et al, 2017). Because both the energy spectra and pitch angle distributions of radiation belt electrons are critically affected by hiss wave scattering (e.g., Ni BB et al, 2013, 2014, 2017, 2019; Zhao H et al, 2019; Li LY et al, 2008; Hua M et al, 2019), and because the scattering rates increase proportionally to the square of hiss amplitude for the near‐resonance cases, our results therefore provide an empirically useful analytic model to be readily used for numerical quantification of hiss‐driven electron diffusion coefficients and global simulations of resultant modulation of radiation belt electron dynamics in response to varying conditions of solar wind and geomagnetic activities.…”