We use high-resolution data from dayside passes of the Magnetospheric Multiscale (MMS) mission to create for the first time a comprehensive listing of encounters with the electron diffusion region (EDR), as evidenced by electron agyrotropy, ion jet reversals, and j • E 0 > 0. We present an overview of these 32 EDR or near-EDR events, which demonstrate a wide variety of observed plasma behavior inside and surrounding the reconnection site. We analyze in detail three of the 21 new EDR encounters, which occurred within a 1-min-long interval on 23 November 2016. The three events, which resulted from a relatively low and oscillating magnetopause velocity, exhibited large electric fields (up to~100 mV/m), crescent-shaped electron velocity phase space densities, large currents (≥2 μA/m 2 ), and Ohmic heating of the plasma (~10 nW/m 3 ). We include an Ohm's law analysis, in which we show that the divergence of the electron pressure term usually dominates the nonideal terms and is much more turbulent on the magnetosphere versus the magnetosheath side of the EDR.Plain Language Summary NASA's Magnetospheric Multiscale (MMS) mission was designed to study magnetic reconnection, a process in which oppositely directed magnetic fields embedded within two neighboring plasma populations annihilate, dumping magnetic energy into the plasmas. Previous missions studying reconnection in space were not fully equipped to analyze how the electrons in the plasma behave near the core of a reconnection site. This study provides MMS researchers with many new reconnection events to dissect, and calls special attention to three events that occurred back to back. Each event included is very unique and helps to fill in another piece of the reconnection puzzle. Perhaps the ultimate goal of these studies is to provide insight into methods of shutting down the reconnection process, which is known to impede attempts toward a stable nuclear fusion engine. A blueprint for stable nuclear fusion could solve mankind's energy needs forever.

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.

On 8 September 2018, at nearly 14:51:30 UT, the Magnetospheric Multiscale (MMS) spacecraftencountered an electron diffusion region near the center of a flux-rope type dipolarization front. The observed signature of the magnetic field in geocentric solar ecliptic included a bipolar B z coinciding with a peak in B y and |B| as is typical for a flux rope. At the same time, all three spacecraft with available plasma data observed a decrease in density and an increase in temperature over ion scales near the reversal in B z . These ion-scale changes are expected in a dipolarization front. The three spacecraft with available electron plasma data also observed clear evidence of electron-scale reconnection just after the B z reversal including ideal magnetohydrodynamics violation, a large out-of-plane current, a large j · E′ energy conversion, and crescent-shaped electron velocity distributions. This is the first time reconnection has been observed near the center of a flux rope on an electron-scale during such an event, and MMS was likely very close to the reconnection X-line. Key Points:• MMS observed an earthward propagating flux rope-type dipolarization front in the near-Earth magnetotail • Electron-scale magnetic reconnection happened near the center of the structure • The X-line motion was such that MMS1 and MMS2 passed through the inner EDR

On December 4, 2017 at approximately 6:15:38 UTC, magnetospheric multiscale (MMS) encountered a reconnecting current sheet near the dayside magnetopause. MMS2 passed through the current sheet just sunward of the southward-moving x-line and observed the crescent-shaped electron velocity distributions associated with reconnection. Additionally, MMS2 observed anti-correlated oscillations in the Hall electric field EN and in the parallel electric field Eǁ at a frequency just below the lower hybrid (LH) frequency. These oscillations appear to be LH drift waves (also called corrugations), which have previously been observed along the dayside magnetopause but were not seen to cause the same kinds of oscillations in the electric field components as observed in this event. It appears that MMS2 periodically crosses a separatrix between the region where EN dominates and a different region where Eǁ dominates at the wave frequency likely due to the wave motion. We also observe energy conversion dominated by Eǁ and veǁ, mostly in the L-direction, in this region as opposed to the reconnection electric field EM and meandering electrons moving in the M-direction as is typically observed during reconnection near an x-line.

We use numerical simulations from the Community Coordinated Modeling Center to provide, for the first time, a coherent temporal description of the magnetic reconnection process of two dayside Electron Diffusion Regions (EDRs) identified in Magnetospheric Multiscale Mission data. The model places the MMS spacecraft near the separator line in these most intense and long-lived events. A listing of 31 dayside EDRs identified by the authors is provided to encourage collaboration in analysis of these unique encounters.