Agyrotropic Electron Distributions in the Terrestrial Foreshock Transients. Issue 4 (22nd February 2023)

• Record Type: Journal Article
• Authors: Gao, C.‐H.; Tang, B.‐B.; Guo, X.‐C.; Li, W. Y.; Khotyaintsev, Y. V.; Graham, D. B.; Turner, D. L.; Yang, Z. W.; Wang, C.
• Is Part Of: Geophysical research letters. Volume 50:Issue 4(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-02-22
• Subjects: agyrotropic electron distributions -- foreshock transients; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL102235
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Agyrotropic electron distributions are frequently taken as an indicator of electron diffusion regions of magnetic reconnection. However, they have also been found at electron‐scale boundaries of the non‐reconnecting magnetopause and are generated by the electron finite gyroradius effect. Here, we present magnetospheric multiscale observations of agyrotropic electron distributions in the foreshock region. These distributions are generated by the electron finite gyroradius effect after magnetic curvature scattering at a thin electron‐scale boundary. Meanwhile, the signatures of magnetic reconnection are absent at this boundary. The test‐particle simulation is adopted to verify the generation of the agyrotropic electron distributions by assuming one‐dimensional magnetic geometry. These observations suggest that agyrotropic electron distributions can be more widely formed at electron‐scale boundaries in space plasma environment. Plain Language Summary: The agyrotropic electron distributions, which could be unstable to generate high frequency electrostatic waves, reveal valuable information of electron dynamics at electron scales. However, due to electron's small mass, the related observational study becomes only possible with the high‐resolution magnetospheric multiscale data. In this study, we show that the agyrotropic electron distributions can be also formed in the foreshock transients such as inside an hot flow anomaly, suggesting that agyrotropic electron distributions are ubiquitous in space plasma. Key Points: We present the first magnetospheric multiscale observations of agyrotropic electron distributions in the foreshock transients Accompanied with the agytropic electron distributions, clear signatures of magnetic reconnection are absent The agytropic electron distributions are formed by the electron finite gyroradius effect at electron‐scale boundaries