Observations of Electron Vortex at the Dipolarization Front

Abstract

Dipolarization front (DF), embedded in fast plasma flow, is a sharp structure with the increase of Bz in a short time and plays an important role in the energy dissipation and particle accelerations in the magnetotail. However, detailed physics at the small scales is still unclear in the DF due to the limitation of the previous mission. In the present study, an electron‐scale plateau in Bz is observed at the DF by Magnetospheric Multiscale (MMS) mission. By analyzing the velocity of the electrons, we find that the electron‐scale plateau is surrounded by a sub‐ion‐scale electron vortex, which is the first observation of electron vortex at the DF as far as we know. The magnetic field generated by the electron vortex cancels parts of the increase of Bz and causes the plateau. Strong asymmetric electric field and demagnetization of electrons and ions are observed at the boundary of the electron vortex. These results shed new light on that small‐scale structures can develop within the ion‐scale DF and affect the evolution and kinetic effects at the DF.

Electron‐Scale Measurements of Antidipolarization Front

“…Particularly, with high‐resolution measurements and small spacecraft separation, the Magnetospheric Multiscale (MMS) mission (Burch et al., 2016) provides an excellent opportunity to investigate the properties of electron‐scale structures at the DFs. The observations of DFs at electron scale verify that the DF surface is not uniform (Jiang et al., 2020; C. M. Liu, Fu, Xu, et al., 2018; D.‐X. Pan et al., 2018), providing a new perspective for investigating the fine structures of the DFs.…”

Observations of Pitch Angle Changes of Electrons and High‐Frequency Wave Activities in the Magnetotail Plasma Bubble

“…At the same time, the total magnetic field decrease obviously. Previous study suggests that the electron vortex can weaken the magnetic field strength (Jiang et al., 2020). However, we have checked the electron velocities and confirmed that no electron vortex occurred during this interval.…”

Observation of High‐Frequency Electrostatic Waves in the Dip Region Ahead of Dipolarization Front

“…Dipolarization front (DF) is a thin boundary layer in the planetary magnetotail. It is characterized by the significant increase of southward (or northward) B z and the decrease of plasma density, usually accompanied by the bursty bulk flow (BBF; Fu, Grigorenko, et al., 2020; Huang et al., 2012; Jiang et al., 2020; Nakamura et al., 2002; Runov et al., 2009). The spatial scale of DF is usually the proton gyroradius or ion inertial length (Fu, Grigorenko, et al., 2020; Fu et al., 2012a, 2012b; Huang, Fu, Vaivadas, et al., 2015; Huang, Yuan, et al., 2015; Huang et al., 2012; Liu, Fu, Vaivads, et al., 2018; Schmid et al., 2011).…”