Electron Bernstein waves driven by electron crescents near the electron diffusion region

W Y Li,C T Russell,R B Torbert,J L Burch,A Vaivads,C Wang,B Lavraud,R E Ergun,B L Giles,W Magnes,Sergio Toledo‐Redondo ,Kayoko Fujimoto ,Per‐Arne Lindqvist ,Cecilia Norgren ,O Le Contel,Daniel B Graham ,D J Gershman,Ferdinand Plaschke ,A C Rager,Kyung-Hwan Min ,Binbin Tang ,Yuri V Khotyaintsev ,Mats André ,Kai Liu ,J Dorelli

doi:10.1038/s41467-019-13920-w

Abstract

The Magnetospheric Multiscale (MMS) spacecraft encounter an electron diffusion region (EDR) of asymmetric magnetic reconnection at Earth’s magnetopause. The EDR is characterized by agyrotropic electron velocity distributions on both sides of the neutral line. Various types of plasma waves are produced by the magnetic reconnection in and near the EDR. Here we report large-amplitude electron Bernstein waves (EBWs) at the electron-scale boundary of the Hall current reversal. The finite gyroradius effect of the outflow electrons generates the crescent-shaped agyrotropic electron distributions, which drive the EBWs. The EBWs propagate toward the central EDR. The amplitude of the EBWs is sufficiently large to thermalize and diffuse electrons around the EDR. The EBWs contribute to the cross-field diffusion of the electron-scale boundary of the Hall current reversal near the EDR.

Highlights

The Magnetospheric Multiscale (MMS) spacecraft encounter an electron diffusion region (EDR) of asymmetric magnetic reconnection at Earth’s magnetopause
Numerical simulations and MMS observations of asymmetric reconnection show that the crescent-shaped agyrotropic electrons can be found on both magnetospheric and magnetosheath sides of the neutral line[3,6,7,8,9]
We report an MMS observation of large-amplitude electron Bernstein waves (EBWs) driven by electron crescents near an EDR

Summary

Results

Electron velocity distributions with enhanced agyrotropies are observed over the magnetopause crossing, including the magnetosheath and magnetospheric sides of the neutral line. All these features indicate that MMS are in or near an electron diffusion region of the magnetopause reconnection[3,5,6,7,9,20,31,32,33,34,35,36]. We present an MMS observation of large-amplitude quasielectrostatic waves at the electron-scale boundary of the Hall current reversal near an EDR encounter.

Discussion

Methods

Code availability