Precipitation of Relativistic Electrons Under Resonant Interaction With Electromagnetic Ion Cyclotron Wave Packets

Abstract

We use numerical simulations to study the resonant interaction of relativistic electrons with rising‐frequency electromagnetic ion cyclotron (EMIC) wave packets in the normalH+ band. We find that precipitating fluxes are formed by quasi‐linear interaction and several nonlinear interaction regimes having opposite effects. In particular, the direct influence of Lorentz force on the particle phase (force bunching) decreases precipitation for particles with low equatorial pitch angles (up to 15–25°) and can even block it completely. Four other nonlinear regimes are possible: nonlinear shift of the resonance point, which can cause pitch angle drift in both directions; phase bunching that slightly increases pitch angle for untrapped particles; directed scattering that strongly decreases pitch angle for untrapped particles; and particle trapping by the wave field that decreases pitch angle. The evolution of the equatorial pitch angle distribution during several passes of particles through the wave packet is studied. The precipitating fluxes are evaluated and compared with theoretical estimates. We show that strong diffusion limit is maintained for a certain range of energies by a wave packet with realistic amplitude and frequency drift. In this case, the quasi‐linear theory strongly underestimates the precipitating flux. With increasing energy, the precipitating fluxes decrease and become close to the quasi‐linear estimates.

Resonant Interaction Of Relativistic Electrons with Realistic Electromagnetic Ion-Cyclotron Wave Packets

“…If the wave amplitude is high enough, then the resonance point is shifted during the interaction. It leads to particles with the same initial pitch angle but different initial phases having different resonance points, and, consequently, different values of R. When dependence R(µ) is significant, that causes drift in µ ( ∆µ = 0) (Grach and Demekhov 2020a). Force bunching (the Lorentz force term in Eq.…”

“…We use the same equations of motion for test electrons interacting with EMIC waves as (Grach and Demekhov 2020a):…”

“…Wave-particle interaction with finite wave packets with various amplitude and frequency profiles has been studied mostly by test particle simulations (Tao et al 2012;Zhang et al 2018;Zhao 2012, 2013;Kubota and Omura 2017;Demekhov 2018a,b, 2020a). Regimes like directed scattering (Kubota and Omura 2017;Grach and Demekhov 2020a,b) or nonlinear shift of the resonance point (Grach and Demekhov 2020a) were revealed and analyzed.…”

“…For EMIC waves, test particle simulations showed that resonant interaction of relativistic electrons with rising-tone EMIC wave packets can be very effective Zhao 2012, 2013;Kubota and Omura 2017;Demekhov 2018b, 2020a). Precipitation flux in this case is heavily influenced and increased by nonlinear effects (Grach and Demekhov 2020a).…”

“…Test particle simulations for resonant interaction with EMIC waves use model wave packets with main parameters based on observations. In particular, our previous paper (Grach and Demekhov 2020a) model wave packets with linear frequency profile and two amplitude profiles, flat and Gaussian-shaped. (Kubota and Omura 2017) used a more complicated structure with several subpackets but without direct correspondence to observational data.…”