Characteristics of Electron Precipitation Directly Driven by Poloidal ULF Waves. Issue 3 (7th March 2023)

• Record Type: Journal Article
• Authors: Yin, Ze‐Fan; Zhou, Xu‐Zhi; Li, Wen; Shen, Xiao‐Chen; Rankin, Robert; Liu, Ji; Hu, Ze‐Jun; Liu, Jian‐Jun; Zong, Qiu‐Gang; Li, Li; Wang, Yong‐Fu
• Is Part Of: Journal of geophysical research. Volume 128:Issue 3(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-03-07
• Subjects: electron precipitation -- ultralow‐frequency waves -- azimuthal electric field -- electron bounce and drift motion -- drift resonance -- pitch‐angle scattering; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2022JA031163
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: A mechanism recently proposed for magnetospheric electron loss into the atmosphere is the precipitation directly driven by ultralow‐frequency (ULF) waves. In this study, we quantitatively analyze the properties of ULF wave‐induced precipitation by simulating the electron bounce and drift motion in poloidal‐mode waves excited in a dipole magnetic field. Our results reveal that precipitation occurs only when electrons encounter a westward‐directed wave electric field in the magnetosphere, which leads to cross‐field energy enhancements and reduces their mirror heights. The simulations also demonstrate longer duration electron precipitation at the drift‐resonance energy. We calculate the temporal variations of the energy spectrum for precipitating electrons and the total precipitating energy fluxes. These results improve our understanding of ULF wave‐induced electron precipitation as well as provide a point of comparison for observations from balloons or ground‐based instruments. Plain Language Summary: Electron precipitation into the atmosphere is a major mechanism for electron loss in the radiation belts. A critical driver for the precipitation is the pitch‐angle scattering induced by various plasma waves in the frequency range between several hertz and tens of kilohertz. On the other hand, ultralow‐frequency (ULF) waves on the order of several millihertz are usually believed to play an indirect role, by modulating other types of waves. Here, we investigate a recently proposed mechanism of electron precipitation directly driven by ULF waves, by simulating electron motion within a poloidal‐mode wave field. The simulations, which cover electron bounce and drift time scales, reveal the important role of the azimuthal wave electric field in the induced electron precipitation. The precipitation occurs when the electrons encounter a westward‐directed electric field, which accelerates the electrons and reduces their mirror heights. The induced precipitation also shows an energy dependence; electrons at the drift‐resonance energy, which encounter a sustained westward‐directed electric field, would have longer precipitation duration than non‐resonant electrons. We further calculate the energy spectrum and the total fluxes of the precipitating electrons directly driven by ULF waves, and demonstrate that the effect could be potentially comparable to that caused by other magnetospheric waves. Key Points: We investigate electron precipitation driven by poloidal‐mode ultralow‐frequency waves that perturb the electron dynamics over bounce and drift timescales Precipitation occurs when electrons encounter westward electric fields, which enhance their cross‐field energy and reduce the mirror heights Drift‐resonant electrons can continuously encounter westward electric fields to have longer precipitation duration than non‐resonant ones