Observations of Electron‐Only Magnetic Reconnection Associated With Macroscopic Magnetic Flux Ropes

Abstract

We report a Magnetospheric Multiscale (MMS) mission observation of magnetic reconnection occurring at the edge of a large-scale magnetic flux rope (MFR), the cross-section of which was about 2 R E. The MFR was observed at the duskside in the Earth's magnetotail and was highly oblique with its axis approximately along the X GSM direction. We find an electron-scale current sheet near the edge of this MFR. The Hall magnetic and electric field, super-Alfvénic electron outflow, parallel electric field, and positive energy dissipation were observed associated with the current sheet, which indicates that MMS detected a reconnecting current sheet with a large guide field. Interestingly, ions were not coupled in this reconnection, akin to the electron-only reconnection observed in the turbulent magnetosheath. We further find that the electron-only reconnection is commonly associated with a macroscopic MFR. This result will shed new light on understanding the multiscale coupling associated with an MFR in space plasmas.

Gyrofluid analysis of electron β e effects on collisionless reconnection

“…There is a wide variety of systems for which this study can be useful, such as magnetosheath plasmas, where current sheets form in the presence of a guide field and a large β e value. Recently, for instance, studies of observations of the magnetospheric multiscale space mission (known as MMS) in the magnetotail have revealed electron-only reconnecting current sheet, where ions do not participate and where β e values can be observed to be greater than 1 (Man et al 2020).…”

“…However, even in the case of a strong guide field, such perturbations can be relevant in some nearly collisionless environments such as the solar wind, which motivates their inclusion in an analysis of collisionless reconnection. The study of reconnection for a finite β e can be relevant especially for plasmas with relatively large temperatures, such as in the Earth's magnetosheath, where some β > 1 values are observed, in the presence of a guide field, during reconnection events (Eastwood et al 2018;Man et al 2020).…”

Electron‐Only Reconnection as a Transition Phase From Quiet Magnetotail Current Sheets to Traditional Magnetotail Reconnection

“…This turbulence can entangle magnetic field lines and generate sub-ion scale reconnection that violates the frozen-in condition and forms electron-only outflow jets (Lapenta et al, 2018;Vega et al, 2020;Zhou et al, 2021). Second, Earthward-traveling plasmoids generated by multiple reconnecting X-lines can reconnect with dipolarized tail field (Vogiatzis et al, 2011) and form a current sheet whose aspect ratio is ripe for electron-only reconnection (Man et al, 2018(Man et al, , 2020. Lastly, during the early stages of traditional reconnection, a short time interval of electron-tearing occurs where only electrons are energized (Lu et al, 2020;Wang et al, 2018Wang et al, , 2020.…”

Three‐Dimensional Electron‐Scale Magnetic Reconnection in Earth's Magnetosphere

“…Thus, this secondary reconnection is essentially a 3-D reconnection as demonstrated in Figure 2b, differing significantly from 2-D reconnection in common knowledge and cannot be accommodated in 2-D magnetopause reconnection. In addition, this secondary reconnection was not responsible for forming this ion-scale MFR, but dissipating this MFR since its core fields were reconnecting which is not expected before (Man et al, 2018(Man et al, , 2020Zhou et al, 2017).…”