Magnetospheric Multiscale Dayside Reconnection Electron Diffusion Region Events

Abstract

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.

Asymmetric Reconnection Within a Flux Rope‐Type Dipolarization Front

“…The MHD violation here is an important difference from a previous study which saw the electron-scale current at a DF boundary being carried by nearly frozen-in electrons (Liu et al, 2018). The maximum agyrotropy as defined by Swisdak (2016) here was 0.053, which is consistent with the 23 EDR candidate events from Webster et al (2018). The maximum agyrotropy as defined by Swisdak (2016) here was 0.053, which is consistent with the 23 EDR candidate events from Webster et al (2018).…”

Crescent‐Shaped Electron Distributions at the Nonreconnecting Magnetopause: Magnetospheric Multiscale Observations

“…In and near EDRs observed by MMS at the dayside magnetopause, crescent-shaped agyrotropic electron distributions perpendicular to the magnetic field have been observed at the magnetospheric side of the EDR (e.g., Chen et al, 2016;Webster et al, 2018) as a result of electron meandering motion in the thin magnetic field reversal (Lapenta et al, 2017), which are consistent with particle simulations (e.g., Bessho et al, 2017;Hesse et al, 2014;Shay et al, 2016). In and near EDRs observed by MMS at the dayside magnetopause, crescent-shaped agyrotropic electron distributions perpendicular to the magnetic field have been observed at the magnetospheric side of the EDR (e.g., Chen et al, 2016;Webster et al, 2018) as a result of electron meandering motion in the thin magnetic field reversal (Lapenta et al, 2017), which are consistent with particle simulations (e.g., Bessho et al, 2017;Hesse et al, 2014;Shay et al, 2016).…”

“…The crescent electrons have a cutoff energy, depending on the electric field in the normal direction and the penetration distance from the separatrix (Egedal et al, 2016), so that they are not filled in at lower energies. Therefore, agyrotropic electron crescents, along with other signatures (such as intense current density and enhanced energy dissipation), are taken as direct observational indicators of an EDR or near-EDR event (e.g., Fuselier et al, 2017;Webster et al, 2018). These electron crescents can become oblique due to the presence of the parallel electric field or the electron inertia if the magnetic field lines rotate rapidly (Egedal et al, 2018).…”

Evidence of Magnetic Nulls in Electron Diffusion Region

“…The recent MMS mission can readily satisfy the first criterion: from September 2015 to electron agyrotropy ( P 2 xy þ P 2 xz þ P 2 Swisdak, 2016) is prominent (Webster et al, 2018), meaning that MMS was located inside the EDRs. The recent MMS mission can readily satisfy the first criterion: from September 2015 to electron agyrotropy ( P 2 xy þ P 2 xz þ P 2 Swisdak, 2016) is prominent (Webster et al, 2018), meaning that MMS was located inside the EDRs.…”