Scattering of energetic electrons through nonlinear cyclotron resonance with coherent whistler-mode hiss emissions

Abstract

Recent observations have revealed that plasmaspheric hiss consists of many discrete waves called “hiss elements.” However, the interaction of energetic electrons (10 keV to several MeV) with the plasmaspheric hiss has only been simulated by the quasilinear (QL) diffusion theory, which does not take the fine wave structure into account. The QL theory cannot address nonlinear particle motions determined by the inhomogeneity factor, which influences the scattering of electrons in pitch angle and energy. This study aims to identify differences between the nonlinear wave–particle interaction and QL theory for plasmaspheric hiss emissions. We conduct test particle simulations to demonstrate the nonlinear interactions between hiss waves and electrons. The nonlinear theory is used to model hiss elements consisting of discrete frequencies and continuous phases. Unlike the other theories, the frequency and amplitude variations in time of the hiss packet are taken into account. Frequencies of the packets are determined to satisfy the separability criterion; when the criterion is met, resonance overlapping is absent, and the electrons can generate each wave element independently. The realistic simulation model of hiss waves reproduces the scattering of electrons by both first- and second-order resonances. We also evaluate the efficiency of electron scattering by calculating nonlinear diffusion coefficients. The diffusion coefficient of equatorial pitch angle is of the same order of magnitude as those calculated by the QL diffusion theory, while we find the effective acceleration of resonant electrons by successive nonlinear trapping, which is not evaluated by the QL theory.

Statistical Analysis of the Differential Deep Penetration of Energetic Electrons and Protons into the Low L Region (L < 4)

“…Energetic electrons in the slot region are subject to nearly continuous scattering loss caused by plasmaspheric hiss waves, VLF transmitter waves, lightning‐generated whistler waves, and others (e.g., Abel & Thorne, 1998; Claudepierre et al., 2020; Xiang et al., 2020). Tens to a few hundred keV electrons are also subject to loss due to the continuous generation of coherent hiss waves inside the plasmasphere and the nonlinear interaction with hiss waves (Omura et al., 2015; Tobita & Omura, 2022). In contrast, the loss of 100s of keV protons at L ∼ 3–4 is mainly caused by charge exchange processes, which is often less efficient than electron loss at this region.…”

Plasmaspheric High‐Frequency Whistlers as a Candidate Cause of Shock Aurora at Earth

“…For RBSP-B (Figure 3l), the intense whistlers below 0.5 f ce seemingly comprised quite dense rising tones, whose overall appearance was close to the hiss; in contrast, the weak whistlers above 0.5 f ce exhibited the clear rising tones. As discussed by Tobita and Omura (2022), the overlapping of waves causes resonant electrons to move chaotically and experience scattering of less nonlinearity. The strong post-shock whistlers below 0.5 f ce could be interpreted as a mixture of many monochromatic waves, whose scattering efficiency on electrons may be reasonably evaluated in the framework of quasi-linear theory (Allanson et al, 2020;Summers et al, 2007aSummers et al, , 2007b.…”