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On 5 May 2017, MMS observed a crater-type flux rope on the dawnside tailward magnetopause with fluctuations. The boundary-normal analysis shows that the fluctuations can be attributed to nonlinear Kelvin-Helmholtz (KH) waves. Reconnection signatures such as flow reversals and Joule dissipation were identified at the leading and trailing edges of the flux rope. In particular, strong northward electron jets observed at the trailing edge indicated midlatitude reconnection associated with the 3-D structure of the KH vortex. The scale size of the flux rope, together with reconnection signatures, strongly supports the interpretation that the flux rope was generated locally by KH vortex-induced reconnection. The center of the flux rope also displayed signatures of guide-field reconnection (out-of-plane electron jets, parallel electron heating, and Joule dissipation). These signatures indicate that an interface between two interlinked flux tubes was undergoing interaction, causing a local magnetic depression, resulting in an M-shaped crater flux rope, as supported by reconstruction.

This paper reports on Magnetospheric Multiscale observations of whistler mode chorus and higher-frequency electrostatic waves near and within a reconnection diffusion region on 23 November 2016. The diffusion region is bounded by crescent-shaped electron distributions and associated dissipation just upstream of the X-line and by magnetic field-aligned currents and electric fields leading to dissipation near the electron stagnation point. Measurements were made southward of the X-line as determined by southward directed ion and electron jets. We show that electrostatic wave generation is due to magnetosheath electron beams formed by the electron jets as they interact with a cold background plasma and more energetic population of magnetospheric electrons. On the magnetosphere side of the X-line the electron beams are accompanied by a strong perpendicular electron temperature anisotropy, which is shown to be the source of an observed rising-tone whistler mode chorus event. We show that the apex of the chorus event and the onset of electrostatic waves coincide with the opening of magnetic field lines at the electron stagnation point.

We present observations on 24 April 2023 by the Magnetospheric Multiscale spacecraft at the dayside, mid‐latitude magnetopause, when an interplanetary magnetic cloud (MC) with sub‐Alfvénic flows and northward and dawnward interplanetary magnetic field components impacted Earth's magnetosphere. The aim is to reveal the processes of solar wind‐magnetosphere interaction under sub‐Alfvénic solar wind with northward magnetic field. Our analysis of electron and ion data suggests that magnetopause reconnection occurred near both polar cusps, forming boundary layers on closed magnetic field lines on both the solar wind (i.e., MC) and magnetospheric sides of the magnetopause. Grad‐Shafranov, electron‐magnetohydrodynamics, and polynomial reconstructions of magnetopause current layers show that local (equator‐of‐the‐cusp) reconnection occurred in a sub‐ion‐scale magnetopause current sheet with a low magnetic shear angle (30°). Interestingly, the local reconnection was observed between the two (MC‐side and magnetosphere‐side) layers of closed field lines. It indicates that reconnected field lines from double cusp reconnection were interacting to induce another reconnection at the mid‐latitude magnetopause. Our results suggest that magnetopause reconnection was more efficient or frequent under sub‐Alfvénic solar wind with much lower beta plasma conditions than typical conditions. We discuss the role of such efficient reconnection in the formation of low‐latitude boundary layers. Plain Language Summary: Solar wind is a supersonic plasma flow emanating from the Sun. On rare occasions, the solar wind at 1 AU can be slower than the Alfvén speed, the speed of transverse electromagnetic waves that propagate in magnetized fluids. Such a sub‐Alfvénic solar wind was observed on 24 April 2023 when a magnetic cloud (MC) with intense magnetic fields, associated with a coronal mass ejection, impinged on Earth's magnetosphere. Interestingly, the MC contained northward interplanetary magnetic field (IMF) components; the way in which sub‐Alfvénic solar wind interacts with Earth's magnetosphere for such IMF conditions is more poorly understood than for southward IMF conditions. In this study, we present observations on this day by NASA's Magnetospheric Multiscale (MMS) spacecraft around the dayside magnetopause, the front‐side boundary of the magnetosphere where the solar wind‐magnetosphere interaction processes occur. Our analysis of MMS data shows that magnetic reconnection at the magnetopause, the plasma physical process shaping and transporting solar wind plasma into the magnetosphere, was more efficient than under normal super‐Alfvénic solar wind conditions. This more efficient reconnection under sub‐Alfvénic solar wind with northward IMF can cause complex interaction of reconnected magnetic field lines and may contribute to more vigorous plasma transport. Key Points: Observations by the Magnetospheric Multiscale mission and reconstruction of magnetopause reconnection under sub‐Alfvénic solar windElectron and ion signatures of dual reconnection near the polar cusps for northward and dawnward interplanetary magnetic field conditionsAdditional reconnection at boundary equatorward of the cusp between closed field lines from dual reconnection and those in magnetosphere [ABSTRACT FROM AUTHOR]

We present in‐depth analysis of three southward‐moving meso‐scale (ion‐to magnetohydrodynamic‐scale) flux transfer events (FTEs) and subsequent crossing of a reconnecting magnetopause current sheet (MPCS), which were observed on 8 December 2015 by the Magnetospheric Multiscale spacecraft in the subsolar region under southward and duskward magnetosheath magnetic field conditions. We aim to understand the generation mechanism of ion‐scale magnetic flux ropes (ISFRs) and to reveal causal relationship among magnetic field structures, electromagnetic energy conversion, and kinetic processes in magnetic reconnection layers. Results from magnetic field reconstruction methods are consistent with a flux rope with a length of about one ion inertial length growing from an electron‐scale current sheet (ECS) in the MPCS, supporting the idea that ISFRs can be generated through secondary reconnection in an ECS. Grad‐Shafranov reconstruction applied to the three FTEs shows that the FTEs had axial orientations similar to that of the ISFR. This suggests that these FTEs also formed through the same secondary reconnection process, rather than multiple X‐line reconnection at spatially separated locations. Four‐spacecraft observations of electron pitch‐angle distributions and energy conversion rate j·E′=j·E+ve×B $\mathbf{j}\cdot {\mathbf{E}}^{\prime }=\mathbf{j}\cdot \left(\mathbf{E}+{\mathbf{v}}_{\mathrm{e}}\times \mathbf{B}\right)$ suggest that the ISFR had three‐dimensional magnetic topology and secondary reconnection was patchy or bursty. Previously reported positive and negative values of j·E′ $\mathbf{j}\cdot {\mathbf{E}}^{\prime }$, with magnitudes much larger than expected for typical MP reconnection, were seen in both magnetosheath and magnetospheric separatrix regions of the ISFR. Many of them coexisted with bi‐directional electron beams and intense electric field fluctuations around the electron gyrofrequency, consistent with their origin in separatrix activities. Plain Language Summary: Magnetic reconnection is a physical process that converts magnetic energy into plasma energy by changing the connectivity of magnetic field lines from one region to another. Magnetic reconnection at the outer boundary of planetary magnetospheres, known as the magnetopause (MP), is key to the entry of solar wind plasma and energy into the magnetospheres that forms the basis for space weather phenomena in the magnetospheres. MP reconnection often occurs in a transient or patchy manner, forming magnetic flux ropes (FRs) with helical field lines of various sizes. They may become an important pathway for fast coupling between the solar wind and magnetosphere. However, the generation mechanism of a subclass of FRs, relatively small "ion‐scale" FRs, is poorly understood. Computer simulations show that they are formed in thin and elongated current sheets of single active reconnection site, but this scenario has not been confirmed by observations. Our observations based on NASA's Magnetospheric Multiscale mission show that ion‐scale FR can form in a thin current sheet of single ongoing reconnection site at Earth's MP. The observed FR showed signatures of complex field line connectivity and localized conversion from electromagnetic to electron energy and vice versa, indicating complex MP dynamics. Key Points: Ion‐scale magnetic flux rope (ISFR) can be generated from reconnecting electron‐scale current sheet at the subsolar magnetopause (MP)Preceding mesoscale flux ropes had axial directions akin to that of the ISFR in the MP, suggesting the same generation mechanismThe ISFR had complex magnetic topology with three‐dimensional effects and involved patchy, intense energy conversion in separatrix regions [ABSTRACT FROM AUTHOR]

Pc5 ultralow frequency waves are important for transferring energy between the magnetosphere and ionosphere. While many observations have been performed on Pc5 waves properties, it has been difficult to determine the source region, signal propagation path, and the two‐dimensional structure of Pc5 waves beyond coverage by a small number of satellites. Pc5 waves often show a dawn‐dusk asymmetry, but the cause of the asymmetry is under debate. To address these issues, we used conjunction events between the THEMIS satellites and all‐sky imagers and analyzed two Pc5 wave events that were stronger on the dawnside. For both events, the Pc5 waves propagated from dawnside magnetopause toward the nightside magnetosphere. The Pc5 waves were also associated with dawnside magnetopause surface waves, which were probably induced by the Kelvin‐Helmholtz instability. The ionospheric equivalent currents identified multiple vortices on the dawnside associated with quasi‐periodic auroral arcs and much weaker perturbations on the duskside. Global auroral imaging also presented a similar dawn‐dusk asymmetry with multiple arcs on the dawnside, while only one or two major arcs existed on the duskside. Pc5 waves in the magnetosphere had an anti‐phase relation between the total magnetic field and thermal pressure, with a slower propagation velocity compared with magnetohydrodynamic waves. The Poynting flux was anti‐sunward with an oscillating field‐aligned component. These properties suggest that Pc5 waves were slow or drift mirror mode waves coupled with standing Alfven waves. The ground‐based and multi‐satellite observations provide crucial information for determining the Pc5 waves properties, possible source region, and signal propagation path. Plain Language Summary: Pc5 ultralow frequency waves (1.66–6.66 mHz) are large‐scale waves in space, and Pc5 waves are capable of interacting with particles and modulating higher frequency waves, resulting in energy transfer in the magnetosphere‐ionosphere system. However, it is difficult to find the exact signal propagation path and identify the source due to the limited sparse satellite observations in space. We investigated two Pc5 wave events by using the conjunctions of ground magnetometers, all‐sky imagers, and Time History of Events and Macroscale Interaction During Substorms (THEMIS) satellites. We found that the aurora shows periodic intensification and the ionospheric currents had multiple vortices with dawn‐dusk asymmetry. The Pc5 waves in the magnetosphere are identified as standing waves that were coupled with surface waves at the magnetopause traveling anti‐sunward. We suggest that magnetopause surface waves were induced by Kelvin‐Helmholtz instability and drive the Pc5 waves. The dawn‐dusk asymmetry of Kelvin‐Helmholtz instability in the magnetosheath may explain the current asymmetric pattern in the ionosphere. Key Points: Two Pc5 wave events we analyzed were highly dawn‐dusk asymmetric, with stronger magnetic field perturbations on the dawnside than dusksideSlow or drift mirror mode waves coupled with standing Alfven waves in the magnetosphere were driven by the magnetopause surface wavesSurface waves by Kelvin‐Helmholtz instability along the magnetopause is suggested to be the source of the dawnside Pc5 waves [ABSTRACT FROM AUTHOR]

We present observations in Earth's magnetotail by the Magnetospheric Multiscale spacecraft that are consistent with magnetic field annihilation, rather than magnetic topology change, causing fast magnetic‐to‐electron energy conversion in an electron‐scale current sheet. Multi‐spacecraft analysis for the magnetic field reconstruction shows that an electron‐scale magnetic island was embedded in the observed electron diffusion region (EDR), suggesting an elongated shape of the EDR. Evidence for the annihilation was revealed in the form of the island growing at a rate much lower than expected for the standard X‐type geometry of the EDR, which indicates that magnetic flux injected into the EDR was not ejected from the X‐point or accumulated in the island, but was dissipated in the EDR. This energy conversion process is in contrast to that in the standard EDR of a reconnecting current sheet where the energy of antiparallel magnetic fields is mostly converted to electron bulk‐flow energy. Fully kinetic simulation also demonstrates that an elongated EDR is subject to the formation of electron‐scale magnetic islands in which fast but transient annihilation can occur. Consistent with the observations and simulation, theoretical analysis shows that fast magnetic diffusion can occur in an elongated EDR in the presence of nongyrotropic electron effects. We suggest that the annihilation in elongated EDRs may contribute to the dissipation of magnetic energy in a turbulent collisionless plasma. Plain Language Summary: Magnetic reconnection in electric current sheets is the key to fast release of magnetic energy in many space and astrophysical plasma systems, such as during magnetospheric substorms and solar flares. Establishing the mechanism by which magnetic energy is converted to particle energy in the reconnection process is the key to understanding the large‐scale impacts of reconnection, including energy partition and particle acceleration. It is generally believed that an electron‐scale diffusion region (EDR), where a magnetic‐to‐electron energy conversion occurs, has an X‐type magnetic field geometry around which the energy of antiparallel magnetic fields injected into the EDR is mostly converted to the bulk‐flow energy of electrons by magnetic tension of reconnected field lines. Contrary to this standard X‐type magnetic field geometry of reconnection, we report observations in Earth's magnetotail by NASA's Magnetospheric Multiscale spacecraft showing that the EDR can be highly elongated. The important and surprising consequence of the observed elongated shape of the EDR is that the fast energy conversion in the EDR can be caused mostly by magnetic field annihilation, rather than magnetic topology change. The fast collisionless annihilation that we discovered is fundamentally different from the classical magnetic field annihilation due to collisional and wave‐induced resistivity. Key Points: Multi‐spacecraft observations consistent with magnetic field annihilation in an electron diffusion region (EDR) of magnetotail reconnectionMagnetic field reconstruction suggests that an electron‐scale magnetic island was embedded in the EDR with elongated shapeTheoretical analysis shows that fast collisionless magnetic diffusion can occur in the elongated part of EDR with nongyrotropic electrons [ABSTRACT FROM AUTHOR]

In‐situ spacecraft missions are powerful assets to study processes that occur in space plasmas. One of their main limitations, however, is extrapolating such local measurements to the global scales of the system. To overcome this problem at least partially, multi‐point measurements can be used. There are several multi‐spacecraft missions currently operating in the Earth's magnetosphere, and the simultaneous use of the data collected by them provides new insights into the large‐scale properties and evolution of magnetospheric plasma processes. In this work, we focus on studying the Earth's magnetopause (MP) using a conjunction between the Magnetospheric Multiscale and Cluster fleets, when both missions skimmed the MP for several hours at distant locations during radial interplanetary magnetic field (IMF) conditions. The observed MP positions as a function of the evolving solar wind conditions are compared to model predictions of the MP. We observe an inflation of the magnetosphere (∼0.7 RE), consistent with magnetosheath pressure decrease during radial IMF conditions, which is less pronounced on the flank (<0.2 RE). There is observational evidence of magnetic reconnection in the subsolar region for the whole encounter, and in the dusk flank for the last portion of the encounter, suggesting that reconnection was extending more than 15 RE. However, reconnection jets were not always observed, suggesting that reconnection was patchy, intermittent or both. Shear flows reduce the reconnection rate up to ∼30% in the dusk flank according to predictions, and the plasma β enhancement in the magnetosheath during radial IMF favors reconnection suppression by the diamagnetic drift. Key Points: Simultaneous observations of the equatorial subsolar magnetopause and dusk flank during time‐extended radial interplanetary magnetic fieldThe magnetosphere enlarges ∼0.7 RE in the subsolar region but <0.2 RE in the flank due to the reduced pressure exerted by the solar windSimultaneous reconnection evidence in the subsolar and flank regions more than 15 RE apart is observed during part of the encounter [ABSTRACT FROM AUTHOR]

Magnetopause Kelvin‐Helmholtz (KH) waves are believed to mediate solar wind plasma transport via small‐scale mechanisms. Vortex‐induced reconnection (VIR) was predicted in simulations and recently observed using NASA's Magnetospheric Multiscale (MMS) mission data. Flux Transfer Events (FTEs) produced by VIR at multiple locations along the periphery of KH waves were also predicted in simulations, but detailed observations were still lacking. Here we report MMS observations of an FTE‐type structure in a KH wave trailing edge during KH activity on 5 May 2017 on the dawnside flank magnetopause. The structure is characterized by (1) bipolar magnetic BY variation with enhanced core field (BZ) and (2) enhanced total pressure with dominant magnetic pressure. The cross‐section size of the FTE is found to be consistent with vortex‐induced flux ropes predicted in the simulations. Unexpectedly, we observe an ion jet (VY); electron parallel heating, ion, and electron density enhancements; and other signatures that can be interpreted as a reconnection exhaust at the FTE central current sheet. Moreover, pitch angle distributions of suprathermal electrons on either side of the current sheet show different properties, indicating different magnetic connectivities. This FTE‐type structure may thus alternatively be interpreted as two interlaced flux tubes with reconnection at the interface as reported by Kacem et al. (2018) and Øieroset et al. (2019s). The structure may be the result of interaction between two flux tubes, likely produced by multiple VIR at the KH wave trailing edge, and constitutes a new class of phenomenon induced by KH waves. Key Points: We present an MMS observation of a Flux Transfer Event‐type structure during a KH event on the dawn flank magnetopause beyond the terminatorIts characteristics are consistent with a structure produced from multiple vortex‐induced reconnection X‐linesReconnection signatures are found at the central current sheet while properties on either side indicate two flux tubes that interlace [ABSTRACT FROM AUTHOR]

We report the observation of solar wind‐magnetosphere‐ionosphere interactions using a series of flux transfer events (FTEs) observed by Magnetospheric MultiScale (MMS) mission located near the dayside magnetopause on 18 December 2017. The FTEs were observed to propagate duskward and either southward or slightly northward, as predicted under duskward and southward interplanetary magnetic field (IMF). The Cooling model also predicted a significant dawnward propagation of northward‐moving FTEs. Near the MMS footprint, a series of poleward‐moving auroral forms (PMAFs) occurred almost simultaneously with those FTEs. They propagated poleward and westward, consistent with the modeled FTE propagation. The intervals between FTEs, relatively consistent with those between PMAFs, strongly suggest a one‐to‐one correspondence between the dayside transients and ionospheric responses. The FTEs embedded in continuous reconnection observed by MMS and corresponding PMAFs individually occurred during persistent auroral activity recorded by an all‐sky imager strongly indicate that those FTEs/PMAFs resulted from the temporal modulation of the reconnection rate during continuous reconnection. With the decay of the PMAFs associated with the FTEs, patch‐like plasma density enhancements were detected to form and propagate poleward and then dawnward. Propagation to the dawn was also suggested by the Super Dual Auroral Radar Network (SuperDARN) convection and Global Positioning System (GPS) total electron content data. We relate the temporal variation of the driving solar‐wind and magnetospheric mechanism to that of the high‐latitude and polar ionospheric responses and estimate the response time. Plain Language Summary: The solar wind‐magnetosphere coupling often occurs in a nonsteady manner. Such disturbances modify the magnetosphere‐ionosphere system. One of the most common/important processes of such nonsteady phenomena is time‐dependent dayside reconnection, as observationally evidenced by flux transfer events (FTEs), which have been, in turn, represented by ionospheric poleward‐moving auroral forms (PMAFs). Decaying PMAFs have, then, been followed by the occurrence of polar cap patches, which are regions of plasma density enhancements observed in the polar cap. This study indicates a sequence of dynamic processes from the driving solar wind, nonsteady reconnection/FTEs, PMAFs, and polar cap patches. Although a portion of this link has been studied and reported, the complete sequence of these connections and full picture of the solar wind‐magnetopause‐ionosphere coupling have rarely been reported and examined. The series of FTEs embedded in continuous reconnection and corresponding PMAFs individually occurred during persistent auroral activity strongly indicate that the FTEs and PMAFs were in response to the temporal modulation of the reconnection rate during continuous reconnection, rather than the repeated, complete turn‐on and turnoff of dayside reconnection. Our study advances the knowledge of Magnetosphere‐Ionosphere‐Coupling near the cusp region and in the open field‐line region that has been less developed than on closed field lines. Key Points: Multiple flux transfer events (FTEs) were observed to form on the dayside magnetopause under southward and duskward IMFGround‐based observations indicate the poleward‐moving plasma streams or auroral forms (PMAFs) associated with the FTEsDevelopment and transpolar motion of polar cap patches following the PMAFs complete the link of solar wind‐magnetosphere‐ionosphere coupling [ABSTRACT FROM AUTHOR]

We present results from the reconstruction of the electron diffusion region of magnetotail reconnection observed by the Magnetospheric Multiscale (MMS) spacecraft on 11 July 2017. In the event, the conditions were suited for the reconstruction technique, developed by Sonnerup et al. (2016, https://doi.org/10.1002/2016JA022430), that produces magnetic field and electron streamline maps based on a two‐dimensional, time‐independent, inertialess form of electron magnetohydrodynamic equation, assuming an approximately symmetric current sheet and negligible guide magnetic field. For such a two‐dimensional and steady structure, the X line orientation can be estimated from a method based on Ampère's law using single‐spacecraft measurements of the magnetic field and electric current density. Our reconstruction results indicate that although the X point was not captured inside its tetrahedron, MMS approached the X point as close as one electron inertial length ~27 km. The opening angle of the recovered separatrix field line, combined with theory, suggests that the dimensionless reconnection rate was 0.17, which is consistent with the measured reconnection electric field 2–4 mV/m. The stagnation point of the reconstructed electron flow is shifted earthward of the X point by ~90 km, one possible interpretation of which is discussed. The energy conversion rate j · E′ in the electron frame tends to be higher near the stagnation point, consistent with earlier observations and simulations, and is not correlated with the amplitude of broadband electrostatic waves observed in the upper‐hybrid frequency range. The latter suggests that the waves did not contribute to energy dissipation in this particular electron diffusion region. Plain Language Summary: Magnetic reconnection is a fundamental plasma process that controls transfer of solar wind energy and mass to planetary magnetospheres and causes explosive energy release associated with solar flares and sudden auroral brightening. National Aeronautics and Space Administration's Magnetospheric Multiscale (MMS) mission, which consists of four identical spacecraft launched in March 2015, aims at elucidating how magnetic reconnection works with unprecedented high temporal and spatial resolution measurements of charged particles and electromagnetic fields in space. MMS has been observing the Earth's magnetotail since May 2017 and encountered the central region of magnetic reconnection, called the electron diffusion region, on 11 July 2017. In this study, we present two‐dimensional images of this region recovered from the MMS electron and magnetic field measurements, showing that the electron flow pattern in the electron diffusion region is not as simple as predicted by theory. The results provide new insights about the reconnection process in the actual space environment. Key Points: Electron MHD reconstruction of a magnetotail reconnection region seen by MMS suggests the dimensionless reconnection rate of 0.17MMS did not capture the X point inside its tetrahedron but was less than one electron inertial length ~27 km away at the closest approachThe recovered electron stagnation point is displaced earthward of the X point by ~90 km, about three times the electron inertial length [ABSTRACT FROM AUTHOR]

We report MMS observations of the ion‐scale flux transfer events (FTEs) that may involve two main X lines and tearing instability between the two X lines. The four spacecraft detected multiple isolated regions with enhanced magnetic field strength and bipolar Bn signatures normal to the nominal magnetopause, indicating FTEs. The currents within the FTEs flow mostly parallel to B, and the magnetic tension force is balanced by the total pressure gradient force. During these events, the plasma bulk flow velocity was directed southward. Detailed analysis of the magnetic and electric field and plasma moments variations suggests that the FTEs were initially embedded within the exhaust region north of an X line but were later located southward/downstream of a subsequent X line. The cross sections of the individual FTEs are in the range of ~2.5–6.8 ion inertial lengths. The observations suggest the formation of multiple secondary FTEs. The presence of an X line in the exhaust region southward of a second X line results from the southward drift of an old X line and the reformation of a new X line. The current layer between the two X lines is unstable to the tearing instability, generating multiple ion‐scale flux‐rope‐type secondary islands. Key Points: MMS observation of ion‐scale flux ropes in the reconnection outflow regionThe initial X line is embedded in the exhaust region downstream of a second X lineFlux transfer events (FTE) are formed between the two X lines due to tearing instability [ABSTRACT FROM AUTHOR]

Abstract: We identify the electron diffusion region (EDR) of a guide field dayside reconnection site encountered by the Magnetospheric Multiscale (MMS) mission and estimate the terms in generalized Ohm's law that controlled energy conversion near the X‐point. MMS crossed the moderate‐shear (∼130°) magnetopause southward of the exact X‐point. MMS likely entered the magnetopause far from the X‐point, outside the EDR, as the size of the reconnection layer was less than but comparable to the magnetosheath proton gyroradius, and also as anisotropic gyrotropic “outflow” crescent electron distributions were observed. MMS then approached the X‐point, where all four spacecraft simultaneously observed signatures of the EDR, for example, an intense out‐of‐plane electron current, moderate electron agyrotropy, intense electron anisotropy, nonideal electric fields, and nonideal energy conversion. We find that the electric field associated with the nonideal energy conversion is (a) well described by the sum of the electron inertial and pressure divergence terms in generalized Ohms law though (b) the pressure divergence term dominates the inertial term by roughly a factor of 5:1, (c) both the gyrotropic and agyrotropic pressure forces contribute to energy conversion at the X‐point, and (d) both out‐of‐the‐reconnection‐plane gradients (∂/∂M) and in‐plane (∂/∂L,N) in the pressure tensor contribute to energy conversion near the X‐point. This indicates that this EDR had some electron‐scale structure in the out‐of‐plane direction during the time when (and at the location where) the reconnection site was observed. [ABSTRACT FROM AUTHOR]

On 8 September 2018, at nearly 14:51:30 UT, the Magnetospheric Multiscale (MMS) spacecraft encountered 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 Bz coinciding with a peak in By 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 Bz. 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 Bz 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 magnetotailElectron‐scale magnetic reconnection happened near the center of the structureThe X‐line motion was such that MMS1 and MMS2 passed through the inner EDR [ABSTRACT FROM AUTHOR]