Energy Conversion and Electron Acceleration in the Magnetopause Reconnection Diffusion Region

Using measurements by the Magnetospheric Multiscale spacecraft in the magnetotail, we studied electron distribution functions across an electron diffusion region. The dependence of the nongyrotropic distribution on the energy and vertical distance from the electron diffusion region midplane was revealed for the first time. The nongyrotropic distribution was observed everywhere except for an extremely narrow layer right at the electron diffusion region midplane. The energy of the nongyrotropic distribution increased with growth of the vertical distance from the midplane. For the electrons within certain energy range, they exhibited the nongyrotropic distribution at the distance further away from the midplane than that expected from the meandering motion. The correlation between the crescent-shaped distribution with multiple stripes and the large Hall electric field was established. It appears that the measured nongyrotropic distribution and the crescent-shaped distribution were caused by the meandering motion and the Hall electric field together. Plain Language SummaryThe Magnetospheric Multiscale mission is designed to study electron physics of magnetic reconnection, a key process for many explosive phenomena in solar flares and magnetosphere. Understanding electron motion is highly important in the study of magnetic reconnection, and the electron velocity distribution is an intuitive and effective way to study the electron dynamics. In this paper, we present a complete electron diffusion region crossing by Magnetospheric Multiscale during a nearly symmetric magnetic reconnection in the magnetotail and show the evolution of the electron velocity distributions across the electron diffusion region. In addition, the relationship between Hall electric field and crescent-shaped electron distribution is also shown in this paper. Key Points:• The electron nongyrotropic distribution depended on the energy and the normal distance from the midplane of the electron diffusion region • The electron crescent distributions were caused by the meandering motion and the Hall electric field together • The fine substructures were observed in the narrow electron diffusion region

Section: Discussion and Summarymentioning

confidence: 68%

Observation of Nongyrotropic Electron Distribution Across the Electron Diffusion Region in the Magnetotail Reconnection

Wang

et al. 2019

“…Figure 1f shows that also overlapping the v eM peaks is a single or binary v eL jet. Such v eL peaks can also be seen in Figure 3 of Pritchard et al (2019). Figure 2 shows results of a reconstruction of the reconnection magnetic field using the polynomial method of Denton et al (2020).…”

Section: April 2018 Eventmentioning

confidence: 65%

“…Their prediction of crescent‐shaped electron distributions was confirmed with data from the NASA Magnetospheric Multiscale (MMS) mission by Burch, Torbert, et al (2016). Pritchard et al (2019) noted the occurrence of converging electron flows in a region of strong out‐of‐plane current and interpreted them as electron inflow velocities to the EDR. Inflow velocities are important because when scaled to the electron Alfvén speed (v Ae ), they provide the reconnection rate (R) (Karimabadi et al, 2013; Klimas, 2015).…”

Section: Introductionmentioning

confidence: 99%

Electron Inflow Velocities and Reconnection Rates at Earth's Magnetopause and Magnetosheath

Burch

Webster

Hesse

et al. 2020

Self Cite

Electron inflow and outflow velocities during magnetic reconnection at and near the dayside magnetopause are measured using satellites from NASA's Magnetospheric Multiscale (MMS) mission. A case study is examined in detail, and three other events with similar behavior are shown, with one of them being a recently published electron‐only reconnection event in the magnetosheath. The measured inflow speeds of 200–400 km/s imply dimensionless reconnection rates of 0.05–0.25 when normalized to the relevant electron Alfvén speed, which are within the range of expectations. The outflow speeds are about 1.5–3 times the inflow speeds, which is consistent with theoretical predictions of the aspect ratio of the inner electron diffusion region. A reconnection rate of 0.04 ± 25% was obtained for the case study event using the reconnection electric field as compared to the 0.12 ± 20% rate determined from the inflow velocity.

“…Observations by MMS2 and MMS4 show no crescent-shaped electron distributions for this interval. Crescent-shaped distributions 10.1029/2020GL087268 have been theorized inside the EDR resulting from a population of meandering electrons (Hesse et al, 2014), demonstrated in simulations (Shay et al, 2016), and observed in other EDR encounters (Chen et al, 2016;Burch et al, 2016;Khotyaintsev et al, 2016;Pritchard et al, 2019;Webster et al, 2018).…”

Section: Electron Velocity Distributionsmentioning

confidence: 98%

Magnetospheric Multiscale Observation of an Electron Diffusion Region at High Latitudes

Burkholder

Nykyri

et al. 2020

Self Cite

On 17 October 2016, Magnetospheric Multiscale (MMS) sampled an electron diffusion region (EDR) embedded in an electron‐scale current sheet within a mixed portion of the high‐latitude magnetosheath adjacent to the magnetopause. We analyze the generalized Ohm's law, dissipation, and electron velocity distributions inside the EDR. The velocities, magnetic fields, and densities observed in the magnetosheath and magnetosphere indicate the magnetopause was unstable to the Kelvin‐Helmholtz instability, which can form electron‐scale current sheets. Alternatively, a current sheet was observed in the solar wind at L1 40 min before the MMS observations, which could have been compressed by the bow shock initiating reconnection. Hundreds of keV particles near the EDR may have been locally accelerated.