Combined Scattering of Radiation Belt Electrons Caused by Landau and Bounce Resonant Interactions With Magnetosonic Waves

Abstract

We develop a full relativistic test particle code to model the combined electron scattering effect of Landau and bounce resonances with magnetosonic waves. Test particle simulations of magnetosonic wave‐electron interactions indicate that the two resonances coexist to affect radiation belt electrons at different energies and pitch angles, and the resultant combined pitch angle scattering and energy diffusion can reach the rates of ~10−4 and ~10‐5 s, respectively, for electrons ~40–500 keV at pitch angles ~ 70 ° – 80° for the given wave model (~200 pT) inside the plasmapause at L = 4.5. Comparisons with the quasi‐linear theory results show that the test particle combined scattering rates are generally an order of magnitude weaker, possibly because the electrons are moved out of the Landau resonance by the advective effect of the bounce resonance. Our investigation demonstrates that the Landau and bounce resonances with magnetosonic waves cannot be treated independently or additively in terms of quasi‐linear theory to simulate the associated radiation belt electron dynamics.

Combined Scattering of Radiation Belt Electrons by Low‐Frequency Hiss: Cyclotron, Landau, and Bounce Resonances

“…Recently, several studies suggest that the MS waves are able to produce the combined scattering effect of electrons by Landau and bounce resonances (e.g., Chen et al, 2015;Fu, Ni, Zhou, et al, 2019;Maldonado et al, 2016), as well as the low-frequency hiss reported in the present study. Those studies discussed that the combination of the two resonances mainly affects the scattering of the near-equatorially mirroring electrons, and the resultant competition between the two resonant mechanisms can produce a nondiffusive scattering.…”

“…An effective way to approach the wave fields is to discretize the incoherent wave spectrum into multiple monochromatic waves at different frequencies. Following the previous studies (e.g., Tao et al, ), the broadband low‐frequency hiss ranging between ω lc = 20 Hz and ω uc = 2000 Hz is discretized into n = 41 plane wave components, that is, ω i = ω k +( i − 1) ⋅ hω ( i = 1,2,3… n ), where hω = ( ω uc − ω lc )/( n − 1) is the bandwidth for each plane wave (e.g., Fu, Ni, Zhou, et al, ; Tao et al, ). Therefore, the magnetic amplitude of each plane wave can be written as to conserve the total energy and the intensity distribution of the hiss, where I B ( ω ) is the power spectral intensity of the wave magnetic field (in pT 2 /Hz).…”

Parametric Dependence of the Formation of Electron Butterfly Pitch Angle Distribution Driven by Magnetosonic Waves

“… Different mechanisms dominate the scattering effect under different conditions. As also demonstrated by Fu et al (2019), inside the plasmapause, Landau and bounce resonances are significant, while the transit‐time effect is not pronounced. Outside the plasmapause, the transit‐time effect and bounce resonance are more important than Landau resonance. Different from some conclusions of previous studies, the coexistence of Landau resonance, bounce resonance, and the transit‐time effect enables MS waves alone to produce electron butterfly PADs. The variation of the ambient plasma density can significantly influence the electron PSD evolution under the impact of MS waves.…”

“…As discussed by this and our previous study (Fu et al, 2019), the scattering effect induced by MS waves is very complicated because Landau and bounce resonant interactions and nonresonant transit‐time scattering can affect the electron dynamics simultaneously. In addition, the competition between the different scattering processes can lead to additional advective scattering over the diffusive processes and reduce the net scattering effect on the radiation belt electrons.…”

Distinct Formation and Evolution Characteristics of Outer Radiation Belt Electron Butterfly Pitch Angle Distributions Observed by Van Allen Probes

“…Magnetosonic waves have been proposed to cause butterfly distributions of both subrelativistic and relativistic electrons due to parallel acceleration through Landau resonance between the waves and electrons (e.g., Li et al, 2014;Li, Bortnik et al, 2016;Li, Ni et al, 2016;Ma et al, 2015;Ni et al, 2017Ni et al, , 2018. Some recent studies reported that the combined effect of the Landau and bounce resonance caused by MS waves tends to reduce the net scattering rates of near equatorially mirroring electrons (Chen et al, 2015;Fu et al, 2019) but is still able to modulate the electron butterfly distribution (Maldonado et al, 2016). Scattering by plasmaspheric hiss is another candidate mechanism for radiation belt electron butterfly PADs at lower L-shells when the wave-induced crossdiffusion is included (Albert et al, 2016).…”