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2020 
Energetic electron dynamics is highly affected by plasma waves through quasilinear and/or nonlinear interactions in the Earth s inner magnetosphere. In this letter, we provide physical explanations for a previously reported intriguing event from the Van Allen Probes observations, where bursts of electron butterfly distributions at tens of keV exhibit remarkable correlations with chorus waves. Both test particle and quasilinear simulations are used to reveal the formation mechanism for the bursts of electron butterfly distribution. The test particle simulation results indicate that nonlinear phase trapping due to chorus waves is the key process to accelerate electrons to form the electron butterfly distribution within ~30 s, and reproduces the observed features. Quasilinear simulation results show that although the diffusion process alone also contributes to form the electron butterfly distribution, the timescale is slower. Our study demonstrates the importance of nonlinear interaction in rapid electron acceleration at tens of keV by chorus waves. Gan, L.; Li, W.; Ma, Q.; Artemyev, A.; Albert, J.; Published by: Geophysical Research Letters Published on: 10/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL090749 butterfly distribution; chorus waves; Electron acceleration; Radiation belts; nonlinear interaction; Van Allen Probes 
Evidence of Nonlinear Interactions Between Magnetospheric Electron Cyclotron Harmonic Waves Electron cyclotron harmonic (ECH) waves play an important role in the magnetosphereionosphere coupling. They are usually considered to be generated by the Bernsteinmode instability with electron loss cone distributions. By analyzing the Van Allen Probes wave data, we present the direct evidence of the nonlinear interactions between ECH waves in the magnetosphere. Substorminjected electrons excite primary ECH waves in a series of structureless bands between multiples of the electron gyrofrequency. Nonlinear interactions between the primary ECH waves produce secondary waves at sum and differencefrequencies of the primary waves. Our results suggest that the nonlinear wavewave interactions can redistribute the primary ECH wave energy over a broader frequency range and hence potentially affect the magnetospheric electrons over a broader range of pitch angles and energies. Gao, Zhonglei; Zuo, Pingbing; Feng, Xueshang; Wang, Yi; Jiang, Chaowei; Wei, Fengsi; Published by: Geophysical Research Letters Published on: 08/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL088452 ECH; wavewave interaction; nonlinear interaction; frequency spectrum broadening; electron Bernstein mode; generalized Bernstein mode; Van Allen Probes 
2018 
Electron nonlinear resonant interaction with short and intense parallel chorus wavepackets One of the major drivers of radiation belt dynamics, electron resonant interaction with whistlermode chorus waves, is traditionally described using the quasilinear diffusion approximation. Such a description satisfactorily explains many observed phenomena, but its applicability can be justified only for sufficiently low intensity, long duration waves. Recent spacecraft observations of a large number of very intense lower band chorus waves (with magnetic field amplitudes sometimes reaching \~1\% of the background) therefore challenge this traditional description, and call for an alternative approach when addressing the global, longterm effects of the nonlinear interaction of these waves with radiation belt electrons. In this paper, we first use observations from the Van Allen Probes and Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft to show that the majority of intense parallel chorus waves consists of relatively short wavepackets. Then, we construct a kinetic equation describing the nonlinear resonant interaction of radiation belt electrons with such short and intense wavepackets. We demonstrate that this peculiar type of nonlinear interaction produces similar effects as quasilinear diffusion, i.e., a flattening of the electron velocity distribution function within a certain energy/pitchangle range. The main difference is the much faster evolution of the electron distribution when nonlinear interaction prevails. Mourenas, D.; Zhang, X.J.; Artemyev, A.; Angelopoulos, V.; Thorne, R.; Bortnik, J.; Neishtadt, A.; Vasiliev, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2018 YEAR: 2018 DOI: 10.1029/2018JA025417 chorus waves; ; kinetic equation; nonlinear interaction; Radiation belts; short wavepackets; trapping; Van Allen Probes 
2017 
Chorus Wave Modulation of Langmuir Waves in the Radiation Belts Using highresolution waveforms measured by the Van Allen Probes, we report a novel observation in the radiation belts. Namely, we show that multiband, discrete, risingtone whistler mode chorus emissions exhibit a onetoone correlation with Langmuir wave bursts. Moreover, the periodic Langmuir wave bursts are generally observed at the phase location where the chorus wave E component is oriented opposite to its propagation direction. The electron measurements show a beam in phase space density at the particle velocity that matches the parallel phase velocity of the chorus waves. Based on this evidence, we conclude that the chorus waves accelerate the suprathermal electrons via Landau resonance and generate a localized electron beam in phase space density. Consequently, the Langmuir waves are excited locally and are modulated by the chorus wave phase. This microscale interaction between chorus waves and highfrequency electrostatic waves provides a new insight into the nonlinear waveparticle interaction process. Li, Jinxing; Bortnik, Jacob; An, Xin; Li, Wen; Thorne, Richard; Zhou, Meng; Kurth, William; Hospodarsky, George; Funsten, Herbert; Spence, Harlan; Published by: Geophysical Research Letters Published on: 12/2017 YEAR: 2017 DOI: 10.1002/2017GL075877 Chorus wave; Landau resonance; Langmuir wave; nonlinear interaction; Radiation belt; Van Allen Probes; wave modulation 
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