Electron beam-associated symmetric electrostatic solitary waves on the separatrix of magnetic reconnection: multi-spacecraft analysis

Shiyou Li,Hong Cai,Shifeng Zhang,Huabo Yang

doi:10.1186/s40623-015-0256-5

Abstract

We present an in situ evidence of electron beam-associated symmetric bipolar electrostatic solitary waves (ESWs) on the current sheet-side of the separatrix of the magnetic reconnection in the near-Earth magnetotail by multi-spacecraft observation of Cluster. Within one spin period, 42 cases of symmetric ESWs are continuously observed during 2 s by SC2 while other spacecrafts do not “detect” them. And the Plasma Electron and Current Experiment (PEACE) spinPAD mode data exhibits unidirectional electron beam antiparallel to the ambient field, and no electron beam-like distribution is found by other spacecrafts without ESW observation. Though the electron beam is strongly associated with the ESWs in observation by multiple spacecraft differentiation, however, the relationship between the counter-directed electron beam and the simultaneously observed ESWs remains unclear and open to the next study.

Highlights

The electrostatic solitary wave (ESW) has been regarded as one means of releasing the energy by carrying electrons out of the generating regions in the natural space
During the spin period with ESW observation, the Plasma Electron and Current Experiment (PEACE) spinPAD mode data exhibits unidirectional electron beam antiparallel to the ambient field and no electron beam-like distribution is found by other spacecrafts without ESW observation
In our previous work (Li et al 2014a), strong and weak electron beams are respectively associated with ESWs on the current sheet-side than on the lobe-side of the separatrix based on mono-point observations

Summary

Introduction

The electrostatic solitary wave (ESW) has been regarded as one means of releasing the energy by carrying electrons out of the generating regions in the natural space. In the process of magnetic reconnection, Cattell et al (2005) suggested that the electron phase space holes (i.e., electron holes) are excited in the separatrix region, near the outer edge of the current sheet, where there are narrow electron beams, either unidirectional or counterstreaming; Fujimoto and Machida (2006) suggested that the electron two-stream instability in association. Direct evidence of electron beam-excited ESWs in the separatrix is rarely reported in the previous studies. In our previous work, Li et al (2014a) reported electron beam-associated ESWs in the tailward outflow region near the separatrix of the magnetic reconnection by Geotail observation.

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Conclusion