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1. Phase Decoherence Within Intense Chorus Wave Packets Constrains the Efficiency of Nonlinear Resonant Electron Acceleration

   https://doi.org/10.1029/2020GL089807  

   Zhang, X. ‐J. ; Agapitov, O. ; Artemyev, A. V. ; Mourenas, D. ; Angelopoulos, V. ; Kurth, W. S. ; Bonnell, J. W. ; Hospodarsky, G. B. ( October 2020 , Geophysical Research Letters)

   Electron resonant interaction with whistler mode waves is traditionally considered as one of the main drivers of radiation belt dynamics. The two main theoretical concepts available for its description are quasi‐linear theory of electron scattering by low‐amplitude waves and nonlinear theory of electron resonant trapping and phase bunching by intense waves. Both concepts successfully describe some aspects of wave‐particle interactions but predict significantly different timescales of relativistic electron acceleration. In this study, we investigate effects that can reduce the efficiency of nonlinear interactions and bridge the gap between the predictions of these two types of models. We examine the effects of random wave phase and frequency variations observed inside whistler mode wave packets on nonlinear interactions. Our results show that phase coherence and frequency fluctuations should be taken into account to accurately model electron nonlinear resonant acceleration and that, along with wave amplitude modulation, they may reduce acceleration rates to realistic, moderate levels.

    

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2. Nonlinear and Synergistic Effects of ULF Pc5, VLF Chorus, and EMIC Waves on Relativistic Electron Flux at Geosynchronous Orbit

   https://doi.org/10.1029/2017JA025003  

   Simms, Laura E. ; Engebretson, Mark J. ; Clilverd, Mark A. ; Rodger, Craig J. ; Reeves, Geoffrey D. ( June 2018 , Journal of Geophysical Research: Space Physics)
3. Nonlinear Interactions Between Radiation Belt Electrons and Chorus Waves: Dependence on Wave Amplitude Modulation

   https://doi.org/10.1029/2019GL085987  

   Gan, L. ; Li, W. ; Ma, Q. ; Albert, J. M. ; Artemyev, A. V. ; Bortnik, J. ( February 2020 , Geophysical Research Letters)

   We use test particle simulations to model the interaction between radiation belt electrons and whistler mode chorus waves by focusing on wave amplitude modulations. We quantify the pitch angle and energy changes due to phase trapping and phase bunching (including both advection and scattering) for electrons with various initial energies and pitch angles. Three nonlinear regimes are identified in a broad range of pitch angle‐energy space systematically, each indicating different nonlinear effects. Our simulation results show that wave amplitude modulations can extend the nonlinear regimes, while significantly reducing electron acceleration by phase trapping. By including amplitude modulations, the “advective” changes in pitch angle and energy caused by phase bunching are reduced, while the “diffusive” scattering due to phase bunching is enhanced. Our study demonstrates the importance of wave amplitude modulations in nonlinear effects and suggests that they need to be properly incorporated into future theoretical and numerical studies.

    

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4. Global Survey of Plasma Sheet Electron Precipitation due to Whistler Mode Chorus Waves in Earth's Magnetosphere

   https://doi.org/10.1029/2020GL088798  

   Ma, Q. ; Connor, H. K. ; Zhang, X. ‐J. ; Li, W. ; Shen, X. ‐C. ; Gillespie, D. ; Kletzing, C. A. ; Kurth, W. S. ; Hospodarsky, G. B. ; Claudepierre, S. G. ; et al ( July 2020 , Geophysical Research Letters)

   Whistler mode chorus waves can scatter plasma sheet electrons into the loss cone and produce the Earth's diffuse aurora. Van Allen Probes observed plasma sheet electron injections and intense chorus waves on 24 November 2012. We use quasilinear theory to calculate the precipitating electron fluxes, demonstrating that the chorus waves could lead to high differential energy fluxes of precipitating electrons with characteristic energies of 10–30 keV. Using this method, we calculate the precipitating electron flux from 2012 to 2019 when the Van Allen Probes were near the magnetic equator and perform global surveys of electron precipitation under different geomagnetic conditions. The most significant electron precipitation due to chorus is found from the nightside to dawn sectors over 4 < L < 6.5. The average total precipitating energy flux is enhanced during disturbed conditions, with time‐averaged values reaching ~3–10 erg/cm²/s whenAE ≥ 500 nT.

    

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5. Ducted Chorus Waves Cause Sub‐Relativistic and Relativistic Electron Microbursts

   https://doi.org/10.1029/2021GL097559  

   Chen, Lunjin ; Zhang, Xiao‐Jia ; Artemyev, Anton ; Angelopoulos, Vassilis ; Tsai, Ethan ; Wilkins, Colin ; Horne, Richard B. ( March 2022 , Geophysical Research Letters)

   During magnetospheric storms, radiation belt electrons are produced and then removed by collisions with the lower atmosphere on varying timescales. An efficient loss process is microbursts, strong, transient precipitation of electrons over a wide energy range, from tens of keV to sub‐relativistic and relativistic energies (100s keV and above). However, the detailed generation mechanism of microbursts, especially over sub‐relativistic and relativistic energies, remains unknown. Here, we show that these energetic electron microbursts may be caused by ducted whistler‐mode lower‐band chorus waves. Using observations of equatorial chorus waves nearby low‐altitude precipitation as well as data‐driven simulations, we demonstrate that the observed microbursts are the result of resonant interaction of electrons with ducted chorus waves rather than nonducted ones. Revealing the physical mechanism behind the microbursts advances our understanding of radiation belt dynamics and its impact on the lower atmosphere and space weather.

    

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