Structure of Electron‐Scale Plasma Mixing Along the Dayside Reconnection Separatrix

Abstract

Interactions between magnetic reconnection inflows and outflows can result in a violent mixing process. In Magnetospheric MultiScale observations of asymmetric, low guide-field reconnection, highly sheared electron flow paired with sharp density and temperature gradients have been found in association with bursts of strong (≥100 mV/m) electric fields parallel to the ambient magnetic field. It is likely that large spikes in E || are part of a dynamic, small-scale structure which results from mixing between plasmas. In this study, a 1-D Vlasov simulation with parameters directly comparable to the observed plasma environment and interaction timescale is used to demonstrate that mixing at a sharp boundary between magnetospheric and magnetosheath electrons is qualitatively consistent with measured particle distributions and signatures in E || . Properties of mixing structures such as net electric potential are estimated and found capable of accelerating electron beams toward the electron diffusion region but are not necessarily sufficient to generate the strongest observed jets. Obliquely propagating lower hybrid drift waves are also present and likely provide most of the energy for acceleration. Drift waves may be responsible for cross-field transport required to begin the mixing process. We conclude that parallel mixing primarily acts to mediate plasma boundaries, thermalizing electron beams contributing to the high anisotropy (T e|| > T e⟂ ) electron distributions found in the dayside reconnection magnetospheric inflow region.

Origin of Electron‐Scale Magnetic Fluctuations Close to an Electron Diffusion Region

“…During the magnetic field fluctuations MMS observes three packets of electrostatic E ∥ fluctuations, likely due to the electron-scale plasma mixing (Figure 4h). However, the amplitude of these fluctuations is only around 10 mV/m, which is one order of magnitude less than the values reported by Holmes et al (2019).…”

“…However, the amplitude of these fluctuations is only around 10 mV/m, which is one order of magnitude less than the values reported by Holmes et al. (2019).…”

Large Amplitude Electrostatic Proton Plasma Frequency Waves in the Magnetospheric Separatrix and Outflow Regions During Magnetic Reconnection

“…The end result is that the plasma is unstable to the generation of various waves which are often found in spacecraft observations. Examples include beam and loss cone driven whistler waves (Graham, Vaivads, et al., 2016; Uchino et al., 2017), electron holes (Farrell et al., 2002; Graham et al., 2015; Holmes et al., 2019), Langmuir waves (Vaivads et al., 2004; Wilder et al., 2016; Zhou et al., 2016), ion acoustic waves (Uchino et al., 2017), and electron acoustic waves (Ergun, Holmes, et al., 2016).…”

The Occurrence and Prevalence of Time Domain Structures in the Kelvin-Helmholtz Instability at Different Positions Along the Earth’s Magnetospheric Flanks

“…These structures include unipolar parallel electric field structures with a net electrostatic potential, such as double layers, as well as bipolar electric field signatures. These bipolar signatures are often referred to as "electrostatic solitary waves" (ESWs), and can refer to several plasma structures such as electron and ion phase space holes (Muschietti et al, 1999;Main et al, 2006), negative potential electron bunching as a result of non-linear whistler waves (Wilder et al, 2016b) and a variety of structures that arise from the mixing of plasmas with differing temperatures (Holmes et al, 2019). One important aspect of TDS, and particularly the readily observable ESWs, is that they are a sign that there is enhanced kinetic activity in plasma.…”