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We report in situ observation of magnetic reconnection between magnetic flux rope (MFR) and magnetic hole (MH) in the magnetosheath by the Magnetospheric Multiscale mission. The MFR was rooted in the magnetopause and could be generated by magnetopause reconnection therein. A thin current sheet was generated due to the interaction between MFR and MH. The sub‐Alfvénic ion bulk flow and the Hall field were detected inside this thin current sheet, indicating an ongoing reconnection. An elongated electron diffusion region characterized by non‐frozen‐in electrons, magnetic‐to‐particle energy conversion, and crescent‐shaped electron distribution was detected in the reconnection exhaust. The observation provides a mechanism for the dissipation of MFRs and thus opens a new perspective on the evolution of MFRs at the magnetopause. Our work also reveals one potential fate of the MHs in the magnetosheath which could reconnect with the MFRs and further merge into the magnetopause. Plain Language Summary: Magnetic flux rope (MFR) is a kind of helical magnetic field structure that is frequently observed in the Earth's magnetosphere. At the dayside magnetopause, MFRs are generally generated by the reconnection of the Earth's intrinsic magnetic field and the interplanetary magnetic field, especially when the interplanetary magnetic field points southward. These MFRs tend to grow larger after they are expelled from the reconnection sites and then travel along the magnetopause, and ultimately disintegrate into the cusp. In this study, we provide another potential fate of these magnetopause MFRs. They can interact with the magnetosheath magnetic holes and dissipate through reconnection with multiple magnetic holes. Based on the Magnetospheric Multiscale observation, we provide direct evidence of reconnection between the MFR and the magnetic hole, which has a pivotal role in this scenario. Our results give new insights into the evolution of MFRs at the magnetopause and further the coupling between the solar wind and the Earth's magnetosphere. Key Points: First observation of magnetic reconnection between magnetic flux rope (MFR) and magnetic hole (MH) in the magnetosheathA thin current sheet with typical reconnection signatures was formed at the interface of MFR and MH due to their interactionAn elongated electron diffusion region was detected in the reconnection exhaust [ABSTRACT FROM AUTHOR]

The Magnetospheric Multiscale (MMS) mission has probed Earth's magnetosphere, magnetosheath, and near‐Earth solar wind for over 8 years. We utilize an unsupervised learning algorithm, Gaussian mixture model clustering, along with feature generation and simple post‐cleaning methods to automatically classify 8 years of MMS dayside observations into four plasma regions (magnetosphere, magnetosheath, solar wind, and ion foreshock) at 1‐min resolution. With these plasma regions distinguished, we have also identified boundary surfaces (e.g., magnetopause, bow shock). We validate our results on manually generated and rule based region labels described in the literature. We report overlap rates in our cluster determined magnetopauses and bow shocks against Scientist‐in‐the Loop (SITL) identified transitions and published databases. Our features are general and our model is extensible, potentially making it applicable to observational data from multiple other missions. Key Points: We use an extensible unsupervised Gaussian mixture model (GMM) algorithm to automatically classify 8 years of dayside magnetospheric multiscale (MMS) plasma dataOur model distinguishes between solar wind, ion foreshock, magnetosheath, and magnetosphere with 97.8% accuracy compared to manual labelsWe provide classified labels and transitions at 1‐min resolution and stable region specific lists for all 8 years of dayside MMS data [ABSTRACT FROM AUTHOR]

Reconnection at Earth's magnetopause drives magnetospheric convection and provides mass and energy input into the magnetosphere/ionosphere system thereby driving the coupling between solar wind and terrestrial magnetosphere. Despite its importance, the factors governing the location of dayside magnetopause reconnection are not well understood. Though a few models can predict X‐line locations reasonably well, the underlying physics is still unresolved. In this study we present results from a comparative analysis of 274 magnetic reconnection events as observed by the Magnetospheric Multiscale (MMS) mission to determine what quantities affect the accuracy of such models and are most strongly associated with the occurrence of dayside magnetopause reconnection. We also attempt to determine under what upstream solar wind conditions each global X‐line model becomes least reliable. Plain Language Summary: Magnetic reconnection is an energy transferring process that happens at the Earth's magnetopause, the boundary between Earth's local plasma environment and the Sun's interplanetary environment. Reconnection helps move energy and particles into the region of space surrounding the earth called the magnetosphere. Dayside reconnection is important because it is a defining element to the amount of energy deposited into our magnetosphere. Despite its importance, scientists still do not completely understand how it works and where it happens. This study looks at many observations of magnetic reconnection to try and understand its precise location and figure out under which conditions it is more likely to occur. This paper compares in situ data with different models for predicting reconnection locations. Key Points: Compared four different reconnection line modelsOn average, the Maximum Bisection Field Model gives the best prediction of reconnection line locationThe Maximum Exhaust Velocity model gives the worst prediction of the reconnection line location [ABSTRACT FROM AUTHOR]

We took a survey of boundary layer (or low-latitude boundary layer) crossings by the Magnetospheric Multiscale (MMS) mission. Out of 250 total crossings, about half showed enhancements of high-energy (> 30 keV) electrons in the FEEPS sensor and a little less than half of those energetic electron events had whistler-mode waves present. Energetic electron enhancements were more likely to be present at magnetic local times closer to noon and at distances of less than about 20 Earth radii, but there was seemingly no correlation with magnetic latitude. For almost all of these events, the pitch angles of the FEEPS electrons were peaked at 90° or isotropic, not field-aligned. Most of the events for which we had data to make a determination showed either direct or indirect evidence of reconnection. Overall, energetic electron enhancements are a fairly common occurrence and there appears to be some connection between whistler waves, energetic electron enhancements, and reconnection, whether it is a direct link or some other process affecting all of them. [ABSTRACT FROM AUTHOR]

The Magnetospheric Multiscale (MMS) mission has presented a new opportunity to study the fine scale structures and phenomena of the Earth's magnetosphere, including cross scale processes associated with the Kelvin–Helmholtz Instability (KHI), but such studies of the KHI and its secondary processes will require a database of MMS encounters with Kelvin–Helmholtz (KH) waves. Here, we present an overview of 45 MMS observations of the KHI from September 2015 to March 2020. Growth rates and unstable solid angles for each of the 45 events were calculated using a new technique to automatically detect plasma regions on either side of the magnetopause boundary. There was no apparent correlation between solar wind conditions during the KHI and its growth rate and unstable solid angle, which is not surprising as KH waves were observed downstream of their source region. We note all KHI were observed for solar wind flow speeds between 295 and 610 km/s, possibly due to a filtering effect of the instability onset criteria and plasma compressibility. Two‐dimensional Magnetohydrodynamic (2D MHD) simulations were compared with two of the observed MMS events. Comparison of the observations with the 2D MHD simulations indicates that the new region sorting method is reliable and robust. The ability to automatically detect separate plasma regions on either side of a moving boundary and determine the KHI growth rate may prove useful for future work identifying and studying secondary processes associated with the KHI. Key Points: A survey of the Magnetospheric Multiscale (MMS) data from September 2015 to March 2020 identified 45 Kelvin–Helmholtz wave eventsEvents are observed for the full range of solar wind conditions. Growth rates are independent of solar wind conditionsA new method is developed for the automatic detection of magnetosheath and magnetospheric regions within the KHI [ABSTRACT FROM AUTHOR]

We investigate the properties of the ion sky maps produced by the Dual Ion Spectrometers (DIS) from the Fast Plasma Investigation (FPI). We have trained a convolutional neural network classifier to predict four regions crossed by the Magnetospheric Multiscale Mission (MMS) on the dayside magnetosphere: solar wind, ion foreshock, magnetosheath, and magnetopause using solely DIS spectrograms. The accuracy of the classifier is >98%. We use the classifier to detect mixed plasma regions, in particular to find the bow shock regions. A similar approach can be used to identify the magnetopause crossings and reveal regions prone to magnetic reconnection. Data processing through the trained classifier is fast and efficient and thus can be used for classification for the whole MMS database. Plain Language Summary: Magnetospheric Multiscale Mission (MMS) has been traversing the Earth's magnetosphere to help scientists understand how the tremendous amounts of energy are released through the phenomenon known as magnetic reconnection. The spacecraft can transfer to the Earth only 4% of its measurements due to link limitations. The success of the mission relies on the selection of the most relevant measurement intervals to be sent down to the science operation center. We have trained a small deep convolutional neural network which identifies the kind of plasma the spacecraft is traversing at each measurement interval with an excellent accuracy >98%. We have used our model to identify some of the most interesting regions, bow shocks. It took only a day for the model to process all observations collected by the MMS within 3 years. The model can save a substantial amount of time for the scientists in the loop whose role is to locate such regions manually. The proposed model is suitable for the hierarchy of models being built to fully automate the on‐ground data processing. Moreover, it is small enough to be embedded in the on‐board software of future missions. Key Points: We develop a technique for automated classification of plasma regions traversed by the Magnetospheric Multiscale Mission spacecraftOur model distinguishes solar wind, megnetosheath, magnetosphere, and ion foreshock with 98% accuracyIt can be used to detect mixed plasma regions, bow shock and magnetopause crossings [ABSTRACT FROM AUTHOR]

Understanding the nature and characteristics of high-frequency waves inside a flux rope may be important as the wave-particle interaction is important for charged-particle energization and the ensuing dissipation process. We analyze waves generated by an electron beam in a crater-shaped magnetic flux rope observed by MMS spacecraft on the dawnside tailward magnetopause. In this MMS observation, a depression of magnetic field, or a crater, of ∼100 km is located at the center of the magnetic flux rope of ∼650 km. There exist parallel and perpendicular electrostatic wave modes inside the depression of the magnetic field at the center of the flux rope, and they are distinguished by their locations and frequencies. The parallel mode exists at the center of the magnetic depression and its power spectrum peaks below Fce (electron cyclotron frequency). In contrast, the perpendicular mode exists in the outer region associated with the magnetic depression, and its power spectrum peaks near Fce. The linear analysis of kinetic instability using a generalized dispersion solver shows that the parallel mode can be generated by the electron beam of 5,000 km/s. They can thermalize electrons ≲100 eV effectively. However, the generation mechanism of the perpendicular mode is not clear yet, which requires further study.

Abstract This article presents 18 magnetic reconnection electron diffusion region (EDR) candidates found using a neural network algorithm with the Magnetospheric Multiscale Mission phase 1a data at the Earth's dayside magnetopause. These new candidates are compared to the 32 previously reported dayside EDRs listed in Webster et al. (2018), https://doi.org/10.1029/2018ja025245, which constitute the training database of our algorithm. One of the main parameters used is a scalar quantity called “MeanRL” which is based on the asymmetry of the electron velocity distribution function and better identifies electron agyrotropy in the plane perpendicular to the magnetic field. In the light of the new EDR candidates found, we discuss and analyze the sign of the energy dissipation during the reconnection process and the distinction between the inner and outer EDRs, with 40% of the candidates showing negative or oscillating dissipation. We also present in details one of the new identified EDR candidates.

This article presents 18 magnetic reconnection electron diffusion region (EDR) candidates found using a neural network algorithm with the Magnetospheric Multiscale Mission phase 1a data at the Earth's dayside magnetopause. These new candidates are compared to the 32 previously reported dayside EDRs listed in Webster et al. (2018), https://doi.org/10.1029/2018ja025245, which constitute the training database of our algorithm. One of the main parameters used is a scalar quantity called "MeanRL" which is based on the asymmetry of the electron velocity distribution function and better identifies electron agyrotropy in the plane perpendicular to the magnetic field. In the light of the new EDR candidates found, we discuss and analyze the sign of the energy dissipation during the reconnection process and the distinction between the inner and outer EDRs, with 40% of the candidates showing negative or oscillating dissipation. We also present in details one of the new identified EDR candidates. Key Points: We report 18 new electron diffusion region (EDR) candidates close to the Earth magnetopause in the Magnetospheric Multiscale Mission (MMS) phase 1a data using a neural networkThe algorithm makes use of a scalar quantity called "MeanRL" to identify the electron perpendicular agyrotropy typical of EDRs from MMS distribution functionsWe analyze and discuss the geometry of EDR based on energy dissipation signatures [ABSTRACT FROM AUTHOR]

Flux ropes are a proposed site for particle energization during magnetic reconnection, with several mechanisms proposed. Here, Magnetospheric Multiscale mission observations of magnetic mirror structures on the edge of two ion‐scale magnetopause flux ropes are presented. Donut‐shaped features in the electron pitch angle distributions provide evidence for electron trapping in the structures. Furthermore, both events show trapping with extended 3D structure along the body of the flux rope. Potential formation mechanisms, such as the magnetic mirror instability, are examined and the evolutionary states of the structures are compared. Pressure and force analysis suggest that such structures could provide an important electron acceleration mechanism for magnetopause flux ropes, and for magnetic reconnection more generally.Key Points: Magnetospheric Multiscale observations show magnetic mirror structures on the edge of magnetopause flux ropesMirror structures trap electrons and have extended 3D structureEvolution of mirror structures could facilitate particle acceleration [ABSTRACT FROM AUTHOR]

Flux transfer events (FTEs), as flux ropes (FRs), are considered key agents for solar wind energy to enter the terrestrial magnetosphere. Recent observations identify entangled flux tubes that collide and pull against each other. Reconnection occurs to disentangle and produce a new pair of FRs with different connectivity. In this paper, we examine the entanglement interface and how such an entanglement process evolves in time by comparing 17 entanglements observed by the Magnetospheric Multiscale (MMS) mission. The By‐dominated interplanetary magnetic field (IMF) distribution of the 17 events agrees with previous findings. We have identified three evolutionary stages characterized by the magnetic field and pressure enhancement. Our study confirms the FR nature of these events and explains how a disparate pair of ropes is formed from two entangled flux tubes, each initially connected to a different hemisphere of the magnetosphere. Plain Language Summary: The Earth's intrinsic magnetic field deflects the solar wind flow at a boundary called the magnetopause. Near this boundary, twisted flux tubes are found. Such tubes may become entangled if they move toward each other, say, from the Southern and Northern Hemispheres. This study analyzes 17 such events and identifies three evolutionary stages as the entanglement proceeds. The results improve our understanding of not only the complex coupling between solar wind and the Earth's magnetic field but other similar processes in space plasma. Key Points: IMF clock angles associated with 17 flux tube entanglement events present peaks near horizontal directionThe entanglement process evolves in three distinguishable stagesMagnetic tension force contributes to the pressure balance at the entanglement interface [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: We present observations of an electron diffusion region (EDR) that was observed well removed from the geomagnetic equator. The EDR is a small volume of the plasma where nonideal physics breaks down and particle acceleration occurs. Magnetic field energy is dissipated as kinetic energy of the plasma, having large‐scale consequences in the plasma even though the conversion occurs on extremely small scales. Access to such small scales has only recently been made possible with the high temporal resolution of instruments on board the Magnetospheric Multiscale spacecraft. Key Points: Observations occur in the dusk sector near the high‐altitude southern geomagnetic cuspParallel electric fields and crescent‐shaped electron distributions indicate MMS crosses through an electron diffusion regionThe observed electron diffusion region occurs at an electron‐scale current sheet near the magnetopause [ABSTRACT FROM AUTHOR]

We analyze the development and influence of turbulence in three‐dimensional particle‐in‐cell simulations of guide field magnetic reconnection at the magnetopause with parameters based on observations from the Magnetospheric Multiscale (MMS) mission. Along the separatrices the turbulence is a variant of the lower‐hybrid‐drift instability (LHDI) that produces electric field fluctuations with amplitudes much greater than the reconnection electric field. The turbulence controls the scale length of the density and current profiles while enabling significant transport across the magnetopause, despite the electrons remaining frozen‐in to the magnetic field. Transport of the out‐of‐plane current density exceeds that of the particle density. Near the X‐line the electrons are not frozen‐in and the turbulence, which differs from the LHDI, makes a significant net contribution to the generalized Ohm's law through an anomalous viscosity. The characteristics of the turbulence and associated particle transport are consistent with fluctuation amplitudes in the MMS observations. However, for this event the simulations suggest that the MMS spacecraft were not close enough to the core of the electron diffusion region to identify the region where anomalous viscosity is important. Key Points: Simulations of magnetopause reconnection develop instabilities similar to observationsFor guide field reconnection, lower‐hybrid drift instability is stabilized at the X‐line but not the separatricesDespite the electrons being frozen‐in, significant transport occurs [ABSTRACT FROM AUTHOR]

At the Earth's magnetopause, the Kelvin‐Helmholtz (KH) instability, driven by the persistent velocity shear between the magnetosheath and the magnetosphere, has been frequently observed during northward interplanetary magnetic field periods and considered as one of the most important candidates for transporting and mixing plasmas across the magnetopause. However, how this process interacts with magnetic field fluctuations, which persistently exist near the magnetopause, has been less discussed. Here we perform a series of 2‐D fully kinetic simulations of the KH instability at the magnetopause considering a power law spectrum of initial fluctuations in the magnetic field. The simulations demonstrate that when the amplitude level of the initial fluctuations is sufficiently large, the KH instability evolves faster, leading to a more efficient plasma mixing within the vortex layer. In addition, when the spectral index of the initial fluctuations is sufficiently small, the modes whose wavelength is longer than the theoretical fastest growing mode grow dominantly. The fluctuating magnetic field also results in the formation of the well‐matured turbulent spectrum with a −5/3 index within the vortex layer even in the early nonlinear growth phase of the KH instability. The obtained spectral features in the simulations are in reasonable agreement with the features in KH waves events at the magnetopause observed by the Magnetospheric Multiscale mission and conjunctively by the Geotail and Cluster spacecraft. These results indicate that the magnetic field fluctuations may really contribute to enhancing the wave activities especially for longer wavelength modes and the associated mixing at the magnetopause. Key Points: The 2‐D fully kinetic simulations of magnetopause Kelvin‐Helmholtz instability initially imposing power law field fluctuations are performedThe growth of the instability especially for long wavelength modes is enhanced by the fluctuating field, leading to more efficient mixingSpectral features obtained from the simulations are in reasonable agreement with past spacecraft observations at the Earth's magnetopause [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]

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. 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/m2), and Ohmic heating of the plasma (~10 nW/m3). 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. Key Points: MMS mapped the EDR and near‐EDR several times during a sequence of new dayside encountersTurbulence in Ohm's law terms is greatest on the magnetospheric‐side EDR, near the plane containing the X line and boundary normal vectorThirty‐two EDR or near‐EDR encounters show crescent‐like enhancements in electron velocity space perpendicular to the local magnetic field [ABSTRACT FROM AUTHOR]

A prediction of the steady state reconnection electric field in asymmetric reconnection is obtained by maximizing the reconnection rate as a function of the opening angle made by the upstream magnetic field on the weak magnetic field (magnetosheath) side. The prediction is within a factor of 2 of the widely examined asymmetric reconnection model (Cassak & Shay, 2007, https://doi.org/10.1063/1.2795630) in the collisionless limit, and they scale the same over a wide parameter regime. The previous model had the effective aspect ratio of the diffusion region as a free parameter, which simulations and observations suggest is on the order of 0.1, but the present model has no free parameters. In conjunction with the symmetric case (Liu et al., 2017, https://doi.org/10.1103/PhysRevLett.118.085101), this work further suggests that this nearly universal number 0.1, essentially the normalized fast-reconnection rate, is a geometrical factor arising from maximizing the reconnection rate within magnetohydrodynamic-scale constraints. [ABSTRACT FROM AUTHOR]

Abstract: We discuss methods to determine L‐M‐N coordinate systems for current sheet crossings observed by the Magnetospheric Multiscale (MMS) spacecraft mission during ongoing reconnection, where eL is the direction of the reconnecting component of the magnetic field, B, and eN is normal to the magnetopause. We present and test a new hybrid method, with eL estimated as the maximum variance direction of B (MVAB) and eN as the direction of maximum directional derivative of B, and then adjust these directions to be perpendicular. In the best case, only small adjustment is needed. Results from this method, applied to an MMS crossing of the dayside magnetopause at 1305:45 UT on 16 October 2015, are discussed and compared with those from other methods for which eN is obtained by other means. Each of the other evaluations can be combined with eL from MVAB in a generalized hybrid approach to provide an L‐M‐N system. The quality of the results is judged by eigenvalue ratios, constancy of directions using different data segments and methods, and expected sign and magnitude of the normal component of B. For this event, the hybrid method appears to produce eN accurate to within less than 10°. We discuss variance analysis using the electric current density, J, or the J × B force, which yield promising results, and minimum Faraday residue analysis and MVAB alone, which can be useful for other events. We also briefly discuss results from our hybrid method and MVAB alone for a few other MMS reconnection events. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the generation and initial utilization of a database containing 80 vector and scalar quantities, for a total of 8,670 magnetopause and magnetosheath current sheet crossings by MMS1, using plasma and magnetic field data from the Fast Plasma Investigation, Fluxgate Magnetometer, and Hot Plasma Composition Analyzer instruments, augmented by solar wind and interplanetary magnetic field data from CDAWeb. Based on a determination of the current sheet width, measured and calculated vector and scalar quantities are stored for the two sides of the current sheet and for selected times within the current sheet. The only manual operations were the classification of the current sheets according to the type of boundary, the character of the magnetic field transition, and the quality of the current sheet fit. To characterize the database, histograms of selected key quantities are presented. We then give the statistics for the duration, motion, and thicknesses of the magnetopause current sheet, using single‐spacecraft techniques for the determination of the normal velocities, obtaining median results of 12.9 s, 38.5 km/s, and 705.4 km, respectively. When scaled to the ion inertial length, the median thickness became 12.6; there were no thicknesses less than one. Next, we apply the Walén relation to find crossings that are rotational discontinuities and thus may indicate ongoing magnetic reconnection. For crossings where the velocities in the outflow region exceed the velocity on the magnetosheath side by at least 250 km/s, 47% meet our rotational discontinuity criteria. If we require the outflow to exceed 250 km/s along the L direction, then the percentage rises to 68%. [ABSTRACT FROM AUTHOR]

Abstract: Data from the NASA Magnetospheric Multiscale mission are used to investigate asymmetric magnetic reconnection at the dayside boundary between the Earth's magnetosphere and the solar wind. High‐resolution measurements of plasmas and fields are used to identify highly localized (~15 electron Debye lengths) standing wave structures with large electric field amplitudes (up to 100 mV/m). These wave structures are associated with spatially oscillatory energy conversion, which appears as alternatingly positive and negative values of J · E. For small guide magnetic fields the wave structures occur in the electron stagnation region at the magnetosphere edge of the electron diffusion region. For larger guide fields the structures also occur near the reconnection X‐line. This difference is explained in terms of channels for the out‐of‐plane current (agyrotropic electrons at the stagnation point and guide field‐aligned electrons at the X‐line). [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we present results from the Magnetospheric Multiscale constellation encountering two ion‐scale, magnetopause flux ropes. The two flux ropes exhibit very different properties and internal structure. In the first flux rope, there are large differences in the currents observed by different satellites, indicating variations occurring over sub‐di spatial scales, and time scales on the order of the ion gyroperiod. In addition, there is intense wave activity and particle energization. The interface between the two flux ropes exhibits oblique whistler wave activity. In contrast, the second flux rope is mostly quiescent, exhibiting little activity throughout the encounter. Changes in the magnetic topology and field line connectivity suggest that we are observing flux rope coalescence. [ABSTRACT FROM AUTHOR]

We compare case studies of Magnetospheric Multiscale (MMS)-observed magnetopause electron diffusion regions (EDRs) to determine how the rate of work done by the electric field [ABSTRACT FROM AUTHOR]

The Magnetosphere Multiscale Mission (MMS) will provide the first opportunity to probe electron-scale physics during magnetic reconnection in Earth's magnetopause and magnetotail. This article will address only tail reconnection-as a non-steady-state process in which the first reconnected field lines advance away from the $x$-point in flux pile-up fronts directed Earthward and anti-Earthward. An up-to-date microscopic physical picture of electron and ion-scale collisionless tail reconnection processes is presented based on 2-D Particle-In-Cell (PIC) simulations initiated from a Harris current sheet and on Cluster and Themis measurements of tail reconnection. The successes and limitations of simulations when compared to measured reconnection are addressed in detail. The main focus is on particle and field diffusion region signatures in the tail reconnection geometry. The interpretation of these signatures is vital to enable spacecraft to identify physically significant reconnection events, to trigger meaningful data transfer from MMS to Earth and to construct a useful overall physical picture of tail reconnection. New simulation results and theoretical interpretations are presented for energy transport of particles and fields, for the size and shape of electron and ion diffusion regions, for processes occurring near the fronts and for the $\mathbf{j} \times \mathbf{B}$ (Hall) electric field. [ABSTRACT FROM AUTHOR]