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We present a new method for determining the main relevant features of the local magnetic field configuration, based entirely on the knowledge of the magnetic field gradient four‐spacecraft measurements. The method, named “magnetic configuration analysis” (MCA), estimates the spatial scales on which the magnetic field varies locally. While it directly derives from the well‐known magnetic directional derivative and magnetic rotational analysis procedures (Shi et al., 2005, htpps://doi.org/10.1029/2005GL022454; Shen et al., 2007, https://doi.org/10.1029/2005JA011584), MCA was specifically designed to address the actual magnetic field geometry. By applying MCA to multispacecraft data from the Magnetospheric Multiscale (MMS) satellites, we perform both case and statistical analyses of local magnetic field shape and dimensionality at very high cadence and small scales. We apply this technique to different near‐Earth environments and define a classification scheme for the type of configuration observed. While our case studies allow us to benchmark the method with those used in past works, our statistical analysis unveils the typical shape of magnetic configurations and their statistical distributions. We show that small‐scale magnetic configurations are generally elongated, displaying forms of cigar and blade shapes, but occasionally being planar in shape like thin pancakes (mostly inside current sheets). Magnetic configurations, however, rarely show isotropy in their magnetic variance. The planar nature of magnetic configurations and, most importantly, their scale lengths strongly depend on the plasma β parameter. Finally, the most invariant direction is statistically aligned with the electric current, reminiscent of the importance of electromagnetic forces in shaping the local magnetic configuration. We define and use a four‐spacecraft method on MMS data to study the magnetic field configuration at small scales in near Earth regionsCase studies demonstrate the ability of the method to measure local magnetic configuration, benchmarking the method on previous studiesStatistically, low plasma betas are correlated with large length scales and slightly more frequent planar shapes in magnetic configurations

We present a three‐dimensional study of the plasma dynamics at the flank magnetopause of the Earth's magnetosphere during mainly northward interplanetary magnetic field periods. Two‐fluid simulations show that the initial magnetic shear at the magnetopause and the field line bending caused by the dynamics itself (in a configuration taken as representative of the properties of the flank magnetopause) influence both the location where the Kelvin‐Helmholtz (KH) instability and the induced magnetic reconnection take place and their nonlinear development. The KH vortices develop asymmetrically with respect to the Earth's equatorial plane where the local KH linear growth rate is maximal. Vortex‐driven reconnection processes take place at different latitudes, ranging from the equatorial plane to midlatitude regions but only in the hemisphere that turns out to be the less KH unstable. These results suggest that KH‐induced reconnection is not limited to specific regions around the vortices (inside, below, or above) but may be triggered over a broad and continuous range of locations in the vicinity of the vortices. Three‐dimensional two‐fluid simulations including of Kelvin‐Helmholtz instability including high‐latitude stabilizationDetailed analysis of the north‐south asymmetric development of the Kelvin‐Helmholtz instabilityDetailed analysis of the north‐south asymmetric development of magnetic reconnection induced by the Kelvin‐Helmholtz vortices

We present theoretical and computational analyses of energy conversions in a magnetized collisionless plasma. We first revisit the theoretical approach to energy conversion analysis and discuss the expected correlations between the different conversion terms. We then present results from a Hybrid‐Vlasov simulation of a turbulent plasma, focusing on the immediate vicinity of a reconnection site. Energy transfers are examined locally and correlations between them are discussed in detail. We show a good anticorrelation between pressure‐driven and electromagnetic acceleration terms. A similar but weaker anticorrelation is found between the heat flux and thermodynamic work acting on internal energies. It is the departure from these anticorrelations that drives the effective changes in the species’ kinetic and internal energies. We also show that overall energy gain or loss is statistically related to the local scale of the system, with higher conversion rates occurring mostly at the smallest local plasma scales. To summarize, we can say that the energization and de‐energization of a plasma is the result of the complex interplay between multiple electromagnetic and thermodynamic effects, which are best taken into account via such a point‐by‐point analysis of the system. We present a novel approach to investigate energy conversions point‐by‐point in a plasma, using a multifluid frameworkWe test the method on a reconnection site generated during the development of plasma turbulence in a hybrid Eulerian simulationEnergy conversions follow from approximate force balance and near‐polytropy, and depend on local characteristic length scales We present a novel approach to investigate energy conversions point‐by‐point in a plasma, using a multifluid framework We test the method on a reconnection site generated during the development of plasma turbulence in a hybrid Eulerian simulation Energy conversions follow from approximate force balance and near‐polytropy, and depend on local characteristic length scales

Using burst mode Magnetospheric Multiscale (MMS) observations in the plasma sheet (PS), we study the dynamics of electron anisotropy and its relation to quasi‐parallel narrowband whistler bursts in 37 dipolarization fronts (DFs) propagating in the Earth's magnetotail along with fast flows at −25 RE≤ X≤ −17 RE. The bursts were observed at the DFs and behind them in the dipolarizing flux bundle (DFB) region with frequencies fpeak~ (0.1–0.6) fce( fceis electron gyrofrequency) and durations approximately a few seconds. The majority of the whistler waves were associated with perpendicular electron temperature anisotropy TPER/TPAR> 1, and the value of this anisotropy decreased by the end of the bursts suggesting electron scattering by the waves. We found that the major contribution to the growth rate of whistler waves is made by resonant electrons with energies Wres~ 1–5 keV and pitch angles αres~ 40–75° and ~100–135°. In the majority of cases, the largest Wreswas observed at the DF and immediately behind it, while in the DFB the Wresdecreased. The sources of the majority of whistler bursts were not confined near the neutral plane but could be extended into the PS where the perpendicular anisotropy of the local electron distribution provided the positive growth rate of the whistler waves. We show that the observed whistler waves play a significant role in the dynamics of electron velocity distribution in DFs, leading to energy exchange between various parts of electron population and constraining temperature anisotropy of electron distribution. Electron distribution function is highly variable on time scalesof short narrowband quasi‐parallel whistler bursts at and behind DFsElectrons with energies 1–5 keV and pitch angles ~40–75° and 100–135° make the major contribution to the growth rate of these wavesThe source of the wave bursts is spread out in space and not confined near the neutral plane

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 BYvariation 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. 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

We investigate both large‐ and small‐scale properties of a Kelvin‐Helmholtz (KH) event at the dusk flank magnetopause using Magnetospheric Multiscale observations on 8 September 2015. We first use two types of 3‐D simulations (global and local) to demonstrate that Magnetospheric Multiscale is close to the most KH unstable region, and so the occurrence of vortex‐induced reconnection may be expected. Because they produce low‐shear current sheets, KH vortices constitute a perfect laboratory to investigate magnetic reconnection with large guide field and low asymmetry. Recent works suggest that magnetic reconnection may be suppressed when a current sheet combines large guide field and pressure gradient (which induces a diamagnetic drift). We thus perform a statistical analysis of high‐resolution data for the 69 KH‐induced low‐shear magnetic reconnection events observed on that day. We find that the suppression mechanism is not at work for most of the observed reconnecting current sheets, as predicted, but we also find that almost all nonreconnecting current sheets should be reconnecting according to this model. This confirms the fact that the model provides a necessary but not sufficient condition for reconnection to occur. Finally, based on the same data set, we study the latitudinal distribution of these magnetic reconnection events combined with global magnetospheric modeling. We find that reconnection associated with KH vortices occurs over a significant range of latitudes at the flank magnetopause. It is not confined to the plane where the growth rate is maximum, in agreement with recent 3‐D simulations. We use two types of global simulations to locate the KH unstable region at the magnetopause and determine its dynamicsWe test the diamagnetic‐drift reconnection suppression condition over 69 very low shear current sheets and find an overall agreementWe report the broad latitudinal extent of magnetic reconnection locations triggered by KH vortices, consistent with bifluid 3‐D simulations

We have used a large number of magnetopause crossings by the Magnetospheric Multiscale (MMS) mission to investigate macroscopic properties of this current sheet, with emphasis on the flanks of the magnetopause. Macroscopic features such as thickness, location, and motion of the magnetopause were calculated as a function of local time sector. The results show that the flanks of the magnetopause are significantly thicker than the dayside magnetopause. Thicknesses vary from about 650 km near noon to over 1,000 km near the terminator. Current densities vary in a similar manner, with average current densities around noon almost twice as high as near the terminator. We also find a dawn‐dusk asymmetry in many of the macroscopic parameters; the dawn magnetopause is thicker than at dusk, while the dusk flank is more dynamic, with a higher average normal velocity. The magnetopause flanks are characterized using MMS observationsMagnetopause flanks are thicker and have lower current density than the daysideThe dawn magnetopause is marginally thicker than at dusk