Plasma waves around separatrix in collisionless magnetic reconnection with weak guide field

Abstract

Electrostatic and electromagnetic waves excited by electron beam around the separatrix region are analyzed in detail during the collisionless magnetic reconnection with a weak guide field by using 2‐D particle‐in‐cell simulation with the adaptive mesh refinement. Broadband electrostatic waves are excited both in the inflow and outflow regions around the separatrices due to the electron bump‐on‐tail, two‐stream, and Buneman instabilities. In contrast, the quasi‐monochromatic electromagnetic waves are excited only in the inflow side of the separatrices due to a beam‐driven whistler instability. The localization of the whistler waves is attributed to the nonuniformity of the out‐of‐plane magnetic field By. The whistler instability is suppressed in the outflow side where By is too small for the oblique propagation. The electrostatic waves with distinct speeds can explain the in situ spacecraft observations. From the causality point of view, the waves are generated as the consequence of the electron bulk acceleration to thermalize the particles through wave‐particle interactions. These simulation results provide guidance to analyze high‐resolution wave observations during reconnection in the ongoing and upcoming satellite missions, as well as in dedicated laboratory experiments.

Electron diffusion region during magnetopause reconnection with an intermediate guide field: Magnetospheric multiscale observations

“…The E M values measured by MMS1, MMS3, and MMS4 are nearly identical, consistent with the uniform E M over d i scale in PIC simulations [e.g., Hesse et al ., , ]. The only exception is the departure between 011739.4 and 011739.5 UT due to a double‐layer‐like structure (similar to those reported in prior studies [ Fujimoto , ; Chen et al ., ; Ergun et al ., ]) registered by MMS1 (based on the burst data, not shown). To further substantiate the E M measurement accuracy, note that MMS3 is outside of the EDR in the sheath inflow, detecting an average E M ~ −0.84 mV/m (Figure f′) and −( V e × B ) M ~ −0.71 mV/m.…”

Electron Acceleration and Thermalization at Magnetotail Separatrices

“…For example, the counter-streaming hot and cold electron populations occurring at reconnection separatrices have been studied extensively with numerical simulations. They have been shown to be unstable to the generation of electrostatic waves, leading to the thermalization of the cold electron beam (Chen et al, 2015;Divin et al, 2012;Egedal et al, 2015;Fujimoto, 2014;Huang et al, 2014). Depending on the velocity at which the waves are generated, they can interact with different parts of the electron distributions (Graham et al, 2015;Omura et al, 1996) and transfer energy between them.…”

Observations of whistler mode waves with nonlinear parallel electric fields near the dayside magnetic reconnection separatrix by the Magnetospheric Multiscale mission

“…Temperature anisotropy due to betatron acceleration in the dipolarization front flux pileup region has also been observed to grow whistler mode waves [e.g., Fujimoto and Sydora, 2008;Khotyaintsev et al, 2011;Viberg et al, 2014]. Numerical simulations of reconnection have shown double layers on the reconnection separatrix, which can produce ESWs in the form of electron phase space holes [Chen et al, 2015]; the Cluster mission observed these double layers on the separatrix during several magnetopause crossings [Wang et al, 2014]. Buneman instabilities can also lead to the generation of ESWs [Che et al, 2010].…”