Resonant scattering of energetic electrons in the plasmasphere by monotonic whistler-mode waves artificially generated by ionospheric modification

S S Chang,X D Gu,Z Y Zhao,J X Li,B B Ni,C Zhou,J Bortnik

doi:10.5194/angeo-32-507-2014

Abstract

Abstract. Modulated high-frequency (HF) heating of the ionosphere provides a feasible means of artificially generating extremely low-frequency (ELF)/very low-frequency (VLF) whistler waves, which can leak into the inner magnetosphere and contribute to resonant interactions with high-energy electrons in the plasmasphere. By ray tracing the magnetospheric propagation of ELF/VLF emissions artificially generated at low-invariant latitudes, we evaluate the relativistic electron resonant energies along the ray paths and show that propagating artificial ELF/VLF waves can resonate with electrons from ~ 100 keV to ~ 10 MeV. We further implement test particle simulations to investigate the effects of resonant scattering of energetic electrons due to triggered monotonic/single-frequency ELF/VLF waves. The results indicate that within the period of a resonance timescale, changes in electron pitch angle and kinetic energy are stochastic, and the overall effect is cumulative, that is, the changes averaged over all test electrons increase monotonically with time. The localized rates of wave-induced pitch-angle scattering and momentum diffusion in the plasmasphere are analyzed in detail for artificially generated ELF/VLF whistlers with an observable in situ amplitude of ~ 10 pT. While the local momentum diffusion of relativistic electrons is small, with a rate of < 10−7 s−1, the local pitch-angle scattering can be intense near the loss cone with a rate of ~ 10−4 s−1. Our investigation further supports the feasibility of artificial triggering of ELF/VLF whistler waves for removal of high-energy electrons at lower L shells within the plasmasphere. Moreover, our test particle simulation results show quantitatively good agreement with quasi-linear diffusion coefficients, confirming the applicability of both methods to evaluate the resonant diffusion effect of artificial generated ELF/VLF whistlers.

Highlights

Generation of extremely low-frequency (ELF)/very lowfrequency (VLF) waves by modulated heating of the D region ionosphere in the presence of naturally forming ionospheric currents is a well-established technique (e.g., Ferraro et al, 1982; Barr and Stubbe, 1991; Inan et al, 2004; Platino et al, 2006; Piddyachiy et al, 2008; and references therein)
We investigate the resonant interaction of artificial ELF/VLF waves with relativistic electrons (1 MeV) at various pitch angles
In this study we have simulated the ray path of ELF/VLF emissions in the inner magnetosphere by assuming that these waves at different frequencies are already generated by modulated HF heating of the ionosphere

Summary

Introduction

Generation of extremely low-frequency (ELF)/very lowfrequency (VLF) waves by modulated heating of the D region ionosphere in the presence of naturally forming ionospheric currents is a well-established technique (e.g., Ferraro et al, 1982; Barr and Stubbe, 1991; Inan et al, 2004; Platino et al, 2006; Piddyachiy et al, 2008; and references therein). To investigate in detail the effect of resonant interactions between artificially generated ELF/VLF whistler waves and energetic electrons in the plasmasphere, instead of adopting the quasi-linear theory that assumes a broadband and incoherent wave field with small wave amplitude, we perform test particle simulations to evaluate the electron diffusion driven by HF heating triggered waves at a single frequency.

Results

Conclusion