Electron Dispersion and Parallel Electron Beam Observed Near the Separatrix

Shi-Chen Bai, Quanqi Shi, Qiu-Gang Zong, Xiaogang Wang, Anmin Tian, Alexander W. Degeling, Chao Yue, I. Jonathan Rae, Zu-Yin Pu, Suiyan Fu

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)


The separatrix region is the region between the separatrix and the reconnection jet. Due to the E×B drift and velocity filter effect in which high‐energy particles with high parallel speed can be seen prior to low‐energy particles along the field line, electrons are separated from ions. The electron dynamics in this region is of interest; however it has not been studied in detail, because of the insufficient resolution of plasma data. We present a slow separatrix crossing event observed by Magnetospheric Multiscale (MMS) satellite constellation on 1 January 2016, from the magnetosheath side with high‐resolution burst mode data. The electron edge and ion edge are clearly distinguished in the separatrix region. Two types of electron dispersion, one with a short duration (~0.3 s) and the other with a longer duration (~13 s) were detected between the electron and ion edges. The rapid dispersion (with small time scale) is mainly in the parallel direction, which might originate from a thin layer with non‐frozen‐in electrons close to the separatrix. The gradual (long time scale) dispersion is seen from parallel to perpendicular directions, which comes from the E×B drift of a curved D‐shape distribution of electrons. The width of the electron diffusion region on the magnetosheath side is estimated based on MMS observation. The observation also reveals an unexpected parallel electron beam outside of the electron edge. Wave‐particle interaction or parallel potential in the inflow region may be responsible for the generation of this electron population.
Original languageEnglish
Pages (from-to)7494-7504
Number of pages11
JournalJournal of Geophysical Research - Space Physics
Issue number9
Early online date9 Sept 2019
Publication statusPublished - Sept 2019
Externally publishedYes


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