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Magnetotail reconnection plays a crucial role in explosive energy conversion in geospace. Because of the lack of in-situ spacecraft observations, the onset mechanism of magnetotail reconnection, however, has been controversial for decades. The key question is whether magnetotail reconnection is externally driven to occur first on electron scales or spontaneously arising from an unstable configuration on ion scales. Here, we show, using spacecraft observations and particle-in-cell (PIC) simulations, that magnetotail reconnection starts from electron reconnection in the presence of a strong external driver. Our PIC simulations show that this electron reconnection then develops into ion reconnection. These results provide direct evidence for magnetotail reconnection onset caused by electron kinetics with a strong external driver.

A three‐dimensional particle‐in‐cell simulation is performed to study secondary reconnection between two interlinked flux tubes produced by neighboring guide field reconnection x‐lines. The reconnecting magnetic fields of this secondary reconnection is enhanced toward the diffusion region, agree well with that in observations. The magnetic field pileup is attributed to the upstream magnetic tension force, that smashes the flux tubes into each other. We propose that the primary reconnection x‐line length is a key parameter to determine the formation of interlinked flux tubes and secondary reconnection therein. Interlinked flux tubes will form only if the x‐line is short; when the x‐line is long enough, the regular flux ropes are formed instead. The critical x‐line length to form interlinked flux tubes is determined by the distance between two neighbor x‐lines and the magnetic shear angle of the primary reconnection. The results provide a novel scenario of secondary reconnection generation during three‐dimensional reconnection. Plain Language Summary: Magnetic reconnection is a fundamental energy conversion process in plasmas, and exists in varieties of space environments. Recent observations find magnetic reconnection occurring in the current sheet between two elbow like flux tubes interlinked with each other. The observational features of such a kind of event are very similar to that of a flux rope, which is a helical magnetic field structure. However, the formation condition for interlinked flux tubes and magnetic reconnection between them is not well understood, the relation between interlinked flux tubes and flux ropes is also not very clear. In this letter, we use three‐dimensional particle‐in‐cell simulation to study the formation of magnetic reconnection between interlinked flux tubes, and propose an explanation for its formation. Key Points: Interlinked flux tubes can form during multiple x‐line guide field reconnection when the x‐line is shortSecondary reconnection can be triggered in the current sheet formed between interlinked flux tubesThe upstream magnetic field pileup is caused by the magnetic tension force [ABSTRACT FROM AUTHOR]

The magnetopause is the boundary between the Earth's magnetosphere and the solar wind. Magnetosheath high‐speed jets can impact the magnetopause, causing local indentation and subsequently rebound. However, the comprehensive response of the magnetopause to the impact of a high‐speed jet remains unclear. In this study, we establish that the full spatiotemporal response pattern of the magnetopause to the impact of an isolated magnetosheath high‐speed jet can be characterized as an "Indentation‐Rebounce‐Relaxation" sequence from a statistical view. Based on the pressure balance, we estimate the spatial and temporal scales of the entire response process to range from 0.5 to 3.2 Earth radii and 0.9–4.7 min, respectively. Furthermore, we find that the interaction between the magnetopause and the high‐speed jet during the rebounce phase distorts the magnetopause, subsequently generating pairs of field‐aligned currents. These generated field‐aligned currents may flow to the ionosphere, potentially contributing to magnetosphere‐ionosphere coupling. Plain Language Summary: The Earth's magnetopause, separating the Earth's magnetosphere from the solar wind, is usually distorted by upstream magnetosheath pressure perturbations. One of these is the magnetosheath high‐speed jets, which are localized dynamic pressure enhancements that can induce the local deformation of the magnetopause. Previous studies have found that magnetosheath high‐speed jets can interact with the magnetopause, causing local indentation and subsequent rebound. However, due to the limitations of in‐situ spacecraft observations, the complete response of the magnetopause to the impact of a high‐speed jet remains unknown. Using Magnetospheric Multiscale satellite data, we establish a comprehensive response pattern of the magnetopause to an HSJ for the first time based on the statistical analysis of multiple cases, which is described as a sequence of "Indentation‐Rebounce‐Relaxation". This study will help us better understand the solar wind‐magnetosphere coupling process. Key Points: The spatiotemporal response of the magnetopause to an isolated HSJ can be sequenced as 'Indentation‐Rebounce‐Relaxation'The estimated spatial and temporal scales of the magnetopause response range from 0.5 to 3.2 Earth radii and 0.9–4.7 min, respectivelyThe high‐speed jet induces deformation of the magnetopause, subsequently generating pairs of field‐aligned currents [ABSTRACT FROM AUTHOR]

Standard magnetic reconnection couples with both ions and electrons on different scales. Recently, a new type of magnetic reconnection, electron‐only reconnection without the coupling of ions, has been observed in various plasma environments. Standard reconnection typically has a reconnection outflow velocity of about one Alfvén speed. According to the scaling analysis, the electron outflow velocity is expected to be about one electron Alfvén speed in electron‐only reconnection. However, observations and simulations both find that the electron outflows are much slower than the electron Alfvén speed. In this letter, by performing two‐dimensional particle‐in‐cell simulations, we show that this is because ions play a role in electron‐only reconnection. The ions move slower than the electrons in the outflow direction, and such charge separation forms an in‐plane Hall electric field, which prevents the electrons from being accelerated to the electron Alfvén speed in electron‐only reconnection. Plain Language Summary: Magnetic reconnection is a fundamental plasma process during which magnetic field line topologies change and magnetic energy transfers to plasma kinetic and thermal energy. In standard collisionless magnetic reconnection, ions and electrons are both heated and accelerated to form high‐speed outflow. Theoretical analyses have been performed to successfully explain the fast outflow speed in standard magnetic reconnection. Recently, a new type of magnetic reconnection, electron‐only reconnection (in which there is no obvious ion heating and acceleration) has been reported to occur in various plasma environments. However, the same scaling analyses performed in electron‐only reconnection overestimate the outflow speed in the electron‐only reconnection by a factor of ∼10. Here, by performing two‐dimensional (2‐D) particle‐in‐cell (PIC) simulations, we show that the overestimation is due to the neglect of the role of ions. Because of the in‐plane Hall electric field caused by charge separation, electron outflow in electron‐only reconnection cannot be accelerated to the expected value. Key Points: Electrons are not accelerated to electron Alfvén speed in electron‐only magnetic reconnectionDeceleration of electron outflow caused by in‐plane Hall electric field should not be ignored [ABSTRACT FROM AUTHOR]

Although initially it was presumed that foreshock waves would propagate directly into the dayside magnetosphere, observational evidence for sinusoidal Pc3 waves in the downstream of quasi‐parallel shocks is scarce. The transmission of these waves from the foreshock into the magnetosphere remains uncertain. In this paper, we employ a 3D global hybrid simulation at a realistic scale to explore the generation and transmission of the dayside ULF waves under a radial interplanetary magnetic field. Our findings demonstrate that the Pc3 waves are self‐consistently generated in the foreshock region and then transmitted into the magnetosheath and magnetosphere. In the foreshock, the waves are excited at approximately 25 mHz and exhibit right‐handed helicity in the plasma frame, characterizing them as quasi‐parallel fast magnetosonic waves. In the magnetosphere, the fluctuating magnetic field is mainly parallel to the background magnetic field, which indicates the dominant wave modes are compressional. Fluctuations in the magnetosheath show a broader spectrum (10–100 mHz) compared to those in the magnetosphere and foreshock, potentially explaining the little observation of sinusoidal Pc3 waves in the magnetosheath. Additionally, only lower frequency compressional waves (below 30 mHz) are effectively transmitted into the dayside magnetosphere. Our simulation provides critical insights into the interactions between the solar wind and Earth's magnetosphere. Plain Language Summary: Ultralow frequency waves in the Pc3 range, with periods of 10–45 s, are frequently detected in the Earth's magnetosphere. These waves are thought to originate from ion foreshock regions upstream of Earth's quasi‐parallel bow shock. They arise from ion beam instabilities triggered by the interaction between shock‐reflected suprathermal ions and the incoming solar wind. While it was assumed that these Pc3 waves would directly enter the dayside magnetosphere, in‐situ observations of sinusoidal Pc3 waves in the magnetosheath remain rare. This scarcity of evidence has left the mechanisms of their propagation into the magnetosphere unclear. This paper employs a 3D global hybrid simulation at a realistic scale to investigate how the Pc3 waves are transmited through the bow shock, magnetosheath, and into the magnetosphere under a radial interplanetary magnetic field. Our results indicate that the Pc3 waves are self‐consistently generated in the foreshock and transmitted into the magnetosheath and magnetosphere, with only lower frequency compressional waves effectively propagating into the magnetosphere. Fluctuations in the magnetosheath exhibit a broader spectrum compared to those in the magnetosphere and foreshock. Key Points: A 3D global hybrid simulation at a realistic scale has been used to investigate the dayside ULF waves under a radial interplanetary magnetic fieldPc 3 waves are self‐consistently generated at the foreshock region and transmitted into the magnetosheath and magnetosphereFluctuations in the magnetosheath exhibit a broad spectrum, and only lower frequency compressional waves are effectively transmitted into the magnetosphere [ABSTRACT FROM AUTHOR]

The 23–24 April 2023 double‐peak (SYM‐H intensities of −179 and −233 nT) intense geomagnetic storm was caused by interplanetary magnetic field southward component Bs associated with an interplanetary fast‐forward shock‐preceded sheath (Bs of 25 nT), followed by a magnetic cloud (MC) (Bs of 33 nT), respectively. These interplanetary structures were led by a coronal mass ejection erupted from the Sun in association with an M1.7 X‐ray flare. At the center of the MC, the plasma density exhibited an order of magnitude decrease, leading to a sub‐Alfvénic solar wind interval for ∼2.1 hr. Ionospheric Joule heating accounted for a significant part (∼81%) of the magnetospheric energy dissipation during the storm main phase. Equal amount of Joule heating in the dayside and nightside ionosphere is consistent with the observed intense and global‐scale DP2 (disturbance polar) currents during the storm main phase. The sub‐Alfvénic solar wind is associated with disappearance of substorms, a sharp decrease in Joule heating dissipation, and reduction in electromagnetic ion cyclotron wave amplitude. The shock/sheath compression of the magnetosphere led to relativistic electron flux losses in the outer radiation belt between L* = 3.5 and 5.5. Relativistic electron flux enhancements were detected in the lower L* ≤ 3.5 region during the storm main and recovery phases. Equatorial ionospheric plasma anomaly structures are found to be modulated by the prompt penetration electric fields. Around the anomaly crests, plasma density at ∼470 km altitude and altitude‐integrated ionospheric total electron content are found to increase by ∼60% and ∼80%, with ∼33% and ∼67% increases in their latitudinal extents compared to their quiet‐time values, respectively. Plain Language Summary: A fast interplanetary coronal mass ejection (ICME) and its upstream sheath caused severe disturbances in the Earth's magnetosphere during 23–24 April 2023. The sheath anti‐sunward of the fast ICME shock was composed of high‐density plasmas and intense magnetic fields. This was followed by a plasma density rarefaction and intense magnetic fields with a field rotation (known as a magnetic cloud). This complex interplanetary structure resulted in a double‐peak geomagnetic storm, and several intense auroral substorms. Solar wind kinetic energy transferred into the magnetosphere during the geomagnetic storm caused large Joule heating in the auroral ionosphere in both dayside and nightside of Earth. Compression of the magnetosphere by the shock/sheath caused losses of relativistic‐energy electrons from the outer radiation belt at the beginning of the magnetospheric event. The equatorial ionospheric anomaly structure, characterized by a low plasma region on the geomagnetic equator and plasma enhancements on both sides (∼±10°) of the equator, was significantly altered during the magnetic storm. In particular, the plasma density crests were more intense and expanded in hemispherical distribution. These variations are attributed to the prompt penetration electric fields to the equatorial ionosphere, which in turn modulated the equatorial ionospheric dynamics. These results should be important for prediction and modeling of geomagnetic storms and their impacts. Key Points: The April 2023 double‐peak geomagnetic storm is a classic event with a sub‐Alfvénic region located in the middle of a magnetic cloudRelativistic electrons displayed classic flux variations and dayside/nightside Joule heating was the dominant storm energy dissipationThe near‐equatorial ionospheric plasma responded to a prompt penetration electric field [ABSTRACT FROM AUTHOR]

We report an Arase‐all sky imager (ASI) conjugate event in which the pulsating aurora (PsA) has a one‐to‐one correspondence with chorus bursts. Wavelet analysis displayed three peaks at ∼0.3 Hz, 4 Hz, and >10 Hz, corresponding to the main pulsation, internal modulation, and fast modulation, respectively. These correspond to the old terms of ∼5–15 s pulsations, chorus risers/elements and subelements/subpackets, respectively. Electron "microbursts" correspond to the 4‐Hz peak. The internal and fast modulations are further verified by the analysis based on fast Fourier transform analyses. Moreover, the spatial distributions of the Fourier spectral amplitude show that the internal and fast modulations are well‐structured within auroral patches. The above results indicate a paradigm shift away from quasilinear theory which implicitly assumes diffuse wave generation. The three time‐scale modulations are consistent with coherent chorus which has been theoretically argued to lead to pitch angle transport three orders of magnitude faster. Plain Language Summary: Pulsating aurora exhibit irregular patches of brightness with quasiperiodic on‐off transitions (∼2–20 s). More rapid modulations, such as internal modulation (∼3–4 Hz) or fast modulation (>10 Hz), have been detected within the pulsation "on" time. However, due to the measurement limitations, the simultaneous observation of three time‐scale modulations has never been reported. In this study, we analyze the conjugate observations of the pulsating aurora (PsA) and chorus recorded by the ground‐based Arase‐all sky imager and the Arase satellite, which demonstrates the coexistence of three time‐scale modulations in the PsA. The spatial distributions of Fourier spectral amplitude show that the internal and fast modulations are well‐structured within the aurora patches. The three time scales of chorus modulation have been previously called chorus 5–15 s pulsations, risers/elements and subelements/subpackets corresponding to the three aurora peaks. This study verifies the existence of internal and fast modulations in PsA, implying an extremely rapid electron loss mechanism. Quasilinear theory cannot explain any of the three time‐scale modulations. The discovery that chorus is coherent and will lead to pitch angle transport 1,000 times faster than diffuse waves is consistent with the fast modulations shown in this paper. A new theory of chorus generation is needed to update that of quasilinear theory. Key Points: We report a conjugate event in which the pulsating aurora (PsA) has a one‐to‐one correspondence with chorus burstsThe frequency spectra of auroral intensities obtained by wavelet analysis and fast Fourier transform (FFT) show the coexistence of ∼0.3 Hz, 4 Hz, and >10 Hz modulationsSpatial distributions show that the internal and fast modulations are well‐structured within aurora patches [ABSTRACT FROM AUTHOR]

Cross‐scale energy transfer is a fundamental problem in plasma physics but is poorly understood. Based on Magnetospheric Multiscale satellite (MMS) data, we present the evidence of the energy transfer between ion‐scale and electron‐scale waves in the Earth's foreshock region. Low‐frequency fast‐magnetosonic waves (LFWs, ∼0.2 Hz; ion‐gyration scales) are observed in the solar wind upstream of the Earth's bow shock. Due to the magnetic compression of LFWs, suprathermal electrons (∼10–100s eV) are adiabatically heated in the perpendicular direction, which leads to the high anisotropy in the high‐magnetic‐field region. Then high‐frequency whistler mode waves (HFWs, 0.1–0.5 fce; electron‐gyration scales) are excited by those anisotropic electrons through cyclotron resonance. Therefore, this study reveals how energy is transported from LFWs to HFWs, suggesting that wave‐particle interactions have played a key role in cross‐scale energy transfer in collisionless plasmas. Plain Language Summary: Cross‐scale energy transfer is a fundamental problem in plasma physics, in which wave‐particle interaction plays an important role. Previous studies provide a limited and incomplete picture of the coupling process between high‐frequency whistler mode waves (HFWs, electron‐scale) and low‐frequency fast‐magnetosonic waves (LFWs, ion‐scale), and therefore further investigation is still needed to clarify their coupling mechanism. Based on MMS satellite data, we present a promising coupling process between HFWs and LFWs in the Earth's foreshock region. Observation results indicate that suprathermal electrons are perpendicularly heated by the LFWs in the high‐magnetic‐field region via betatron acceleration. These electrons could generate the HFWs through cyclotron resonance, which is confirmed by both observations and theoretical calculations. Therefore, this event shows the energy transfer among LFWs, suprathermal electrons, and HFWs, illustrating that the energy is directly transported from the ion scale to the electron scale. Our finding provides a potential generation mechanism for HFWs, which may be highly important for understanding the electron dynamics in the Earth's foreshock region. Key Points: Using Magnetospheric Multiscale satellite data, we present the evidence of the energy transfer from ion‐scale low‐frequency fast‐magnetosonic waves (LFWs) to electron‐scale high‐frequency whistler mode waves (HFWs) in the Earth's foreshock regionDue to the magnetic compression of the LFWs, suprathermal electrons (∼10–100s eV) are adiabatically heated in the perpendicular directionBoth theoretical analysis and observations suggest that the HFWs are excited by those suprathermal electrons through cyclotron resonance [ABSTRACT FROM AUTHOR]

Superposed epoch analyses were performed on 193 significant relativistic electron flux dropout events, in order to study the roles of different solar wind parameters in driving the depletion of relativistic electrons, using '16 years of data from the POES and GOES missions, and the OMNIWEB solar wind database. We find that the solar wind dynamic pressure and interplanetary magnetic field (IMF) Bz play key roles in causing the relativistic electron flux dropouts, but also that either large solar wind dynamic pressure or strong southward IMF Bz by itself is capable of producing the significant depletion of relativistic electrons. The relativistic electron flux dropouts occur not only when the magnetopause is compressed closer to the Earth but also when the magnetopause is located very far (>'10 RE). Importantly, our results show that in addition to the large solar wind dynamic pressure, which pushes the magnetopause inward strongly and causes the electrons to escape from the magnetosphere, relativistic electrons can also be scattered into the loss cone and precipitate into the Earth's atmosphere during periods of strong southward IMF Bz, which preferentially provides a source of free energy for electromagnetic ion cyclotron (EMIC) wave excitation. This is supported by the fact that the strongest electron precipitation into the atmosphere is found in the dusk sector, where EMIC waves are typically observed in the high-density plasmasphere or plume and cause efficient electron precipitation down to '1 MeV.

Magnetosheath jets with enhanced dynamic pressure are common in the Earth's magnetosheath. They can impact the magnetopause, causing deformation of the magnetopause. Here we investigate the 3‐D structure of magnetosheath jets using a realistic‐scale, 3‐D global hybrid simulation. The magnetosheath has an overall honeycomb‐like 3‐D structure, where the magnetosheath jets with increased dynamic pressure surround the regions of decreased dynamic pressure resembling honeycomb cells. The magnetosheath jets downstream of the bow shock region with θBn ≲ 20° (where θBn is the angle between the upstream magnetic field and the shock normal) propagate approximately along the normal direction of the magnetopause, while those downstream of the bow shock region with θBn ≳ 20° propagate almost tangential to the magnetopause. Therefore, some magnetosheath jets formed at the quasi‐parallel shock region can propagate to the magnetosheath downstream of the quasi‐perpendicular shock region. Plain Language Summary: Magnetosheath jets are high‐speed transient structures frequently observed in the magnetosheath, and they can impact and dent the magnetopause. However, their three‐dimensional (3‐D) structure is still under debt despite decade‐long research. By performing high‐resolution, 3‐D numerical simulation, we reveal that the magnetosheath has an overall honeycomb‐like 3‐D structure where the jets surround regions with lower plasma velocity resembling honeycomb cells. Key Points: Magnetosheath jets are studied by a realistic‐scale, 3‐D global hybrid simulation under a radial interplanetary magnetic field (IMF)The magnetosheath has a honeycomb‐like 3D structure where regions of increased dynamic pressure surround those of decreased dynamic pressureThe magnetosheath jets formed at the quasi‐parallel shock can propagate to the magnetosheath downstream of the quasi‐perpendicular shock [ABSTRACT FROM AUTHOR]

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]

Magnetosheath high‐speed jets (HSJs), localized impulses of dynamic pressure, are attracting growing attention due to their geoeffectiveness. However, how HSJs modulate chorus waves in the magnetosphere still remains unclear. Utilizing combined observations of the Time History of Events and Macroscale Interactions during Substorms satellites A and E, we report, for the first time, the prompt disappearance of the magnetospheric chorus waves caused by a HSJ. Such wave disappearance is directly due to the flux drop of energetic electrons (∼10–100 keV), leading to the cessation of wave generation, which is supported by the linear theoretical analysis. We propose that the flux drop results from the local indentation of magnetopause after the HSJ impact, where two new smaller magnetic mirrors are formed off the equator and part of electrons are then expelled by the mirror force. The HSJs should be an important factor in modulating chorus waves because of their high occurrence rate. Plain Language Summary: The solar wind with enhanced dynamic pressure can globally compress the dayside magnetosphere, causing the excitation and intensification of chorus waves. Besides the enhancement of solar wind RAM pressure, there also exists the ion‐scale dynamic pressure impulse in the magnetosheath, known as a high‐speed jet (HSJ), even during quiet solar wind conditions. Previous studies have shown that the HSJs have a high occurrence rate and they are geoeffective (causing disturbances in the Earth's magnetosphere). However, it is still unknown whether HSJs can modulate chorus waves in the magnetosphere. In this study, based on joint observations of THEMIS‐A and E probes, we report the prompt disappearance of chorus waves in the magnetosphere caused by the HSJs. We propose that a HSJ causes the local indentation of the dayside geomagnetic fields at the magnetic equator, and creates two small magnetic mirrors. Consequently, the poleward mirror force will expel some of the electrons from the equator, and lead to a significant decrease of the electron flux. Finally, the generation of chorus waves will stop due to the lack of energy sources. This study reveals that HSJs are a new and important factor in modulating chorus waves in the magnetosphere. Key Points: With joint observations of THMIS‐A and THMIS‐E, we first report the prompt disappearance of chorus waves due to the high‐speed jets (HSJs)HSJs cause the local indentation of the magnetopause, creating two new magnetic mirrors, and electrons are expelled by the mirror forceThe electron flux drop leads to the cessation of the chorus wave generation, that is, the disappearance of waves [ABSTRACT FROM AUTHOR]

Magnetic reconnection can effectively convert magnetic energy into plasma energy, and accelerate electrons. In this article, the electrons with energies up to 150 keV are observed in the separatrix region and near the electron diffusion region (EDR) detected by the Magnetospheric Multiscale mission in the magnetotail. Combined with the electron pitch‐angle distribution, the electrons in these two regions have a striking behavior: the low‐energy electrons (<∼10 keV) move mainly toward the X‐line, while the energetic electrons (69–139 keV) move mainly away from the X‐line. In the EDR, the energy of electrons can reach up to 10 keV and there is a notable enhancement in the flux of electrons in the direction perpendicular to the magnetic field, which implies the presence of acceleration processes occurring in the EDR, leading to the energization of electrons. Furthermore, the energy spectrum of non‐thermal electron with energies above 6 keV shows a power law distribution in this event, suggesting the occurrence of multiple acceleration processes rather than a single energization mechanism. These findings underscore the EDR's role as a crucial region for electron acceleration during magnetic reconnection. The study provides essential clues about the mechanisms driving electron acceleration, contributing to our understanding of space weather phenomena and the broader dynamics of plasma physics in space environments. Key Points: Energetic electrons with energies up to 150 keV are observed near the electron diffusion region in Earth's magnetotailLow‐energy electrons move mainly toward the X‐line, while energetic electrons move mainly away from the X‐lineNon‐thermal electrons (>6 kV) in these regions show power‐law spectrum, indicating that the electrons have been accelerated efficiently [ABSTRACT FROM AUTHOR]

Thin current sheets (TCS) formed in Earth's magnetotail and hosting magnetic field line reconnection are important element of magnetospheric dynamics. In this paper, a statistical survey of 163 TCS crossing events in Earth's magnetotail using observations by MMS during 2017–2020 is performed. We find that magnetotail TCSs typically have a very strong current density primarily carried by electrons, with a thickness of a few ion inertial lengths. Our statistical results reveal different characteristics between TCSs located on the duskside and dawnside. Specifically, we find that TCSs on the duskside have a smaller thickness, higher current density, and stronger Hall electric field than on the dawnside. Our results also show that there is a correlation between the TCS thickness and the Hall electric field magnitude, with a stronger Hall electric field present in thinner TCSs. Our statistics results confirm previously reported key TCS dawn‐dusk asymmetries, with the main advance of directly measurable plasma currents. TCS characteristics of the presented data set will be useful for initialization of realistic numerical simulations and theoretical investigations of TCS instabilities resulted in various dynamical models of the magnetotail. Key Points: We collect a data set of 163 thin current sheet crossing events in Earth's magnetotail using MMS data during 2017–2020The thin current sheet has a smaller thickness, a higher current density and a stronger Hall electric field on the duskside than the dawnsideThe Hall electric field in the magnetotail thin current sheet is stronger when the current sheet is thinner [ABSTRACT FROM AUTHOR]