On the Nature of Intense Sub‐Relativistic Electron Precipitation

• Published in: Journal of geophysical research. Space physics Vol. 127; no. 6
• Main Authors: Artemyev, A. V., Zhang, X.‐J., Zou, Y., Mourenas, D., Angelopoulos, V., Vainchtein, D., Tsai, E., Wilkins, C.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01.06.2022; Wiley-Blackwell
• Subjects: Altitude; Chorus waves; Cyclotron resonance; Electron precipitation; Electrons; Ionosphere; landau resonance; Magnetospheres; Microbursts; Microbursts (meteorology); precipitation; Radiation; Radiation belts; Relativistic effects; Resonance; Resonance scattering; Spacecraft; Whistlers; whistler‐mode waves
• ISSN: 2169-9380; 2169-9402; 2169-9402
• DOI: 10.1029/2022JA030571

Energetic electron precipitation into Earth's atmosphere is an important process for radiation belt dynamics and magnetosphere‐ionosphere coupling. The most intense form of such precipitation is microbursts—short‐lived bursts of precipitating fluxes detected on low‐altitude spacecraft. Due to the wide energy range of microbursts (from sub‐relativistic to relativistic energies) and their transient nature, they are thought to be predominantly associated with energetic electron scattering into the loss cone via cyclotron resonance with field‐aligned intense whistler‐mode chorus waves. In this study, we show that intense sub‐relativistic microbursts may be generated via electron nonlinear Landau resonance with very oblique whistler‐mode waves. We combine a theoretical model of nonlinear Landau resonance, equatorial observations of intense very oblique whistler‐mode waves, and conjugate low‐altitude observations of <200 keV electron precipitation. Based on model comparison with observed precipitation, we suggest that such sub‐relativistic microbursts occur by plasma sheet (0.1 − 10 keV) electron trapping in nonlinear Landau resonance, resulting in acceleration to ≲200 keV energies and simultaneous transport into the loss cone. The proposed scenario of intense sub‐relativistic (≲200 keV) microbursts demonstrates the importance of very oblique whistler‐mode waves for radiation belt dynamics. Key Points We report on intense sub‐relativistic electron precipitation events observed by ELFIN CubeSats Sub‐relativistic precipitation events are due to electron nonlinear Landau resonance with very oblique whistler waves Sub‐relativistic precipitation events may indicate an enhancement of equatorial energetic electron fluxes