Potential Evidence of Low‐Energy Electron Scattering and Ionospheric Precipitation by Time Domain Structures

• Published in: Geophysical research letters Vol. 47; no. 16
• Main Authors: Shen, Yangyang, Artemyev, Anton, Zhang, Xiao‐Jia, Vasko, Ivan Y., Runov, Andrei, Angelopoulos, Vassilis, Knudsen, David
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.08.2020
• Subjects: Auroras; Broadband; Cyclotrons; Diffuse aurora; Electron cyclotron waves; electron holes; Electron precipitation; electron scattering; Electrons; Fluctuations; injections; Ionosphere; Low altitude; Magnetosphere-ionosphere coupling; Nonlinear waves; Outflow; Pitch (inclination); Plasma; plasma sheet precipitation; Precipitation; Scattering; Spacecraft; Structures; Time domain analysis; time domain structures
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2020GL089138

Plasma sheet electron precipitation is critical in magnetosphere‐ionosphere coupling and has long been attributed to electron scattering by whistler‐mode and electron cyclotron harmonic waves. Recent observations have revealed that time domain structures (TDSs) that appear as broadband electrostatic fluctuations may also scatter plasma sheet electrons. However, there has been no observational evidence of TDS scattering electrons into the ionosphere. This study presents potential evidence from conjugate observations between the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission and the low‐altitude Enhanced Polar Outflow Probe (e‐POP) spacecraft. During the five events presented, THEMIS observed intense electron injections accompanied by TDSs, while e‐POP captured precipitation of plasma sheet electrons with energies ∼100–325 eV over a broad pitch angle range. The observed TDSs can efficiently scatter these electrons exceeding the strong diffusion limit. Our results suggest that TDSs may contribute to plasma sheet electron scattering around times of injections. Plain Language Summary Plasma sheet electron precipitation into the diffuse aurora has long been attributed to electron scattering by whistler and electron cyclotron waves. Recent studies have revealed a class of nonlinear wave structures that may also scatter plasma sheet electrons, namely, time domain structures (TDSs) appearing as broadband electrostatic fluctuations in frequency space. However, such scattering process has not been confirmed by observations. This study presents potential evidence from spacecraft observations in the magnetosphere and ionosphere. Our novel results show that TDSs in the near‐equatorial plasma sheet can efficiently scatter plasma sheet electrons during disturbed times and thus should be included in future models of auroral electron precipitation. Key Points We report observations of plasma sheet electron precipitation associated with time domain structures (TDSs) We show potential evidence that TDSs can scatter low‐energy (≤1 keV) plasma sheet electrons which contribute to diffuse auroras Observed TDSs can cause strong diffusion to fill the loss cone of plasma sheet electrons and produce significant precipitating energy fluxes