Resonant Scattering of Radiation Belt Electrons by Discrete Multi-Frequency ELF/VLF Waves From Ionospheric Heating

Abstract

This study investigates the resonant interactions between artificial Extremely Low Frequency and Very Low Frequency waves, generated via modulated ionospheric heating, and energetic electrons in Earth's radiation belts. Using test particle simulations, we analyze how discrete multi-frequency waves (with characteristics derived from DEMETER observations) scatter electrons, examining the dependence on wave frequency, electron energy, and equatorial pitch angle. Key findings reveal that higher-frequency waves resonate with a broader range of electrons but at higher magnetic latitudes, while lower-frequency waves are more effective for pitch-angle scattering. Multi-frequency waves, even with modest amplitudes (e.g., 10 pT per frequency), significantly enhance diffusion rates, particularly for 100–300 keV electrons near the loss cone, achieving bounce-averaged pitch-angle diffusion coefficients of ∼10⁻⁴/s. The results demonstrate strong energy dependence, with sub-MeV electrons exhibiting higher scattering rates than MeV-range populations. Diffusion coefficients generally increase with equatorial pitch angle but exhibit non-monotonic fluctuations due to the detuning of lower-frequency components. These findings highlight the potential use of ionospheric heating to artificially modulate radiation belt dynamics and suggest that multi-frequency wave generation could optimize electron scattering efficiency. This study bridges observational data with theoretical modeling, providing insights for future experiments aimed at controlled electron precipitation.