Agyrotropic Electron Distributions in the Terrestrial Foreshock Transients

Abstract

AbstractAgyrotropic 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.