Role of Ducting in Relativistic Electron Loss by Whistler‐Mode Wave Scattering

Abstract

Near-equatorial and ground-based measurements of whistler-mode waves are accompanied by relativistic electron precipitation • In the presence (absence) of ducted wave propagation, as monitored by propagation to the ground, the precipitating electron energies are above (below) 150 keV • Ducted whistler-mode waves may play a key role in relativistic electron loss in the inner magnetosphere

Short Chorus Wave Packets: Generation Within Chorus Elements, Statistics, and Consequences on Energetic Electron Precipitation

“…Figure 11b shows that J precip obtained from the simulation with β = 5 and a constant B w , peak = 160 pT (with an occurrence rate of wave packets adjusted to have a time‐averaged wave intensity $$\langle {B}_{w}^{2}(t)\rangle =7{0}^{2}$$ pT 2 ) remains in good agreement with J precip,QL over more than three decades of precipitating flux between 50 and 330 keV (compare green filled diamonds and solid magenta curve). This confirms that resonant interactions with independent, short, and moderately intense chorus wave packets essentially correspond to a regime of quasi‐linear electron diffusion (Artemyev, Neishtadt, Vasiliev, et al., 2021; Mourenas et al., 2018; Zhang, Agapitov, et al., 2020).…”

“…In test particle simulations, the distance between wave packets is taken equal to packet length. In this case, particles near the loss cone that escape from resonant trapping (Artemyev, Neishtadt, Albert, et al., 2021 ; Kitahara & Katoh, 2019 ) usually cannot be trapped by the next packet, which is roughly equivalent to having large random phase jumps between packets as in chorus wave statistics (Zhang, Agapitov, et al., 2020 )—a situation roughly equivalent to considering independent wave packets. All the above parameters are consistent with statistical observations in the dawn sector at L ∼ 6 during similar moderately disturbed periods (Agapitov et al., 2018 ; Mourenas et al., 2021 ; Sheeley et al., 2001 ; Zhang, Mourenas, et al., 2020 ; Zhang et al., 2018 ).…”

Relativistic electron precipitation by EMIC waves: importance of nonlinear resonant effects

“…Panels (b,c) confirm that increases of trapped fluxes are accompanied by strong precipitation of relativistic electrons. There are two important features of this transient precipitation: First, precipitating fluxes and ratio of precipitating-to-trapped fluxes maximize at relativistic energies (> 700 keV) without a significant precipitation of < 500 keV electrons, which would indicate electron scattering by whistler-mode waves (compare the precipitation at 13:21:05 UT and precipitation likely driven by plasmaspheric hiss at 13:20:35-13:20:45 UT; also see the discussion of ELFIN observations of whistler-mode wave driven precipitation in Mourenas et al (2021);Artemyev, Demekhov, et al (2021)); Second, precipitating fluxes at relativistic energies (around ∼ 1 MeV) almost reach the strong diffusion limit (see the comparison of precipitating and trapped electron spectra in panel (e)). These two features strongly suggest that the observed precipitation is driven by electron scattering by EMIC waves (see similar equatorial observations of small pitch-angle flux enhancements associated with EMIC waves in Zhu et al, 2020), which resonate with relativistic electrons most effectively (Albert, 2003;Kersten et al, 2014;Ni et al, 2015;Shprits et al, 2017) and are well able to cause precipitation in the strong diffusion limit (Omura & Zhao, 2013;Kubota & Omura, 2017;Grach & Demekhov, 2020).…”

On the Role of Whistler‐Mode Waves in Electron Interaction With Dipolarizing Flux Bundles

“…To check this, we compare model results with observations from the low‐altitude, polar‐orbiting CubeSats ELFIN (Angelopoulos et al., 2020) that provide conjugate measurements for the event in Figure 8 (see Figure 12g for details of ELFIN and THEMIS orbits). Energetic particle detectors on board ELFIN measure electron pitch‐angle and energy distributions, and thus allow us to investigate electron fluxes within the loss‐cone j loss as well as trapped fluxes j trap (see details in, e.g., Artemyev, Demekhov, et al., 2021; Mourenas et al., 2021). We use 1.5 s (half‐spin) time resolution ELFIN measurements, which provides full pitch‐angle resolution.…”

“…As the electron bounce time is much faster than their adiabatic transport and associated heating, several incidents of wave trapping and scattering can occur around the equator before the electron energy can evolve adiabatically due to transport. Therefore, electron energy changes occur cyclically, each cycle comprising large energy increases due to trapping and gradual energy decreases due to bunching (see details in Artemyev, Neishtadt, et al., 2021). To mimic wave generation at the magnetic field minimum and propagation along magnetic field lines, we assume that wave amplitude B w grows from zero at the equator to saturation at a peak value at some off‐equatorial distance beyond which it stays constant (see the empirical models for the the inner magnetosphere, e.g., Agapitov et al., 2015, 2018).…”