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

Abstract

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.

Magnetosphere‐Ionosphere Coupling of Precipitated Electrons in Diffuse Aurora Driven by Time Domain Structures

“…Here, we present the initial STET code simulations results that describe the interaction of TDSs with magnetospheric electrons. We mostly will be focusing on the MI coupling of this phenomena as initially predicted by Vasko, Agapitov, Mozer, Artemyev, Krasnoselskikh, and Bonnell (2017) and Vasko et al (2018) and experimentally supported by Shen et al (2020) using THEMIS and e-POP observations. We briefly outlined all of these previous results in Sections 2 and 3.…”

“…We used the pitch-angle diffusion calculations, D αα , to analyze the electron MI energy interplay in the region of diffuse aurora driven by TDSs at L-shells 6 and 8. The D αα calculation presented by Vasko, Agapitov, Mozer, Artemyev, Krasnoselskikh, and Bonnell (2017) and Vasko et al (2018) and Shen et al (2020), as well as shown in Figures 1h and 1i of this manuscript, was based on the dipole magnetic field geometry. To be consistent with these calculations, we, correspondingly, used the same magnetic field topology for the STET code.…”

“…This letter, for the first time, considers MI energy interplay of precipitated electrons in the diffuse aurora that are driven by TDSs in the presence of atmospheric backscatter from two magnetically conjugate regions. Using THEMIS-observed TDSs from Shen et al (2020) at L = 8 (Section 2), and corresponding pitch-angle diffusion coefficients calculation based on theoretical studies by Vasko, Agapitov, Mozer, Artemyev, Krasnoselskikh, and Bonnell (2017), Vasko, Agapitov, Mozer, Artemyev, Drake, and Kuzichev (2017 (Section 3), we analyzed the different physical scenario of the formation of precipitated and upward electron fluxes in the diffuse aurora that are driven by TDSs at the L shells 6 and 8 (Section 4 and 5).…”

“…TDSs Spectral PropertiesTo evaluate electron diffuse auroral precipitation driven by TDS scattering in the STET code, we need to estimate electron local diffusion coefficients due to TDSs, which requires observations of TDS spectral properties, such as average TDS spectral intensities and TDS parameters along with the background plasma density and magnetic field. Here, we will use a reported example of THEMIS-observed TDSs fromShen et al (2020) at L = 8.…”

Why Atmospheric Backscatter Is Important in the Formation of Electron Precipitation in the Diffuse Aurora

“…Additional evidence of MI precipitated electron energy interplay in aurora were discussed in recent experimental studies by Shen et al. (2020) and Artemyev et al. (2020).…”