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The tailward high‐speed flows, in which various kinetic processes and magnetic structures can be embedded, are usually produced by the magnetic reconnection in the Earth's magnetotail. Here, using high‐resolution measurements from the Magnetospheric Multiscale (MMS) mission, we report an intense current in the tailward high‐speed flow. The current density can reach ∼180 nA/m2 and is primarily carried by electrons. Taking advantage of the First‐Order Taylor Expansion (FOTE) method, we reveal that such an intense current is associated with a ribbon‐like magnetic structure. A large electric field, reaching ∼90 mV/m, is also observed at the magnetic structure. The Hall term dominates the electric field, however, the contribution from the pressure gradient term and the electron inertial term is nonnegligible and can lead to strong energy conversion (E ⋅ J > 2 nW/m3) through the synergistic action with the intense current. This study improves the understanding of the current behaviors and energy conversion associated with magnetic structures in the Earth's magnetotail. Plain Language Summary: As products of the magnetotail magnetic reconnection, the earthward and tailward high‐speed flows can be usually observed as associated with a variety of kinetic processes and magnetic structures. Here, for the first time, we report an electron‐carried intense current associated with a ribbon‐like magnetic structure in the tailward high‐speed flow, by using high‐resolution MMS data and the First‐Order Taylor Expansion (FOTE) method. Encountering a large electric field with a nonnegligible contribution from the pressure gradient term and electron inertial term, such intense current leads to a strong energy conversion at the ribbon‐like magnetic structure. This study shed light on how the intense current is associated with the ribbon‐like magnetic structure and how the strong energy conversion is driven at such a structure, which complements the knowledge of the energy conversion process in the Earth's magnetotail. Key Points: An electron‐carried intense current (J > 180 nA/m2) is observed in association with a ribbon‐like structure in the tailward high‐speed flowA large electric field, with nonnegligible contribution from pressure gradient and electron inertial term, is observed at such a structureThe intense current and large electric field work together to drive a strong energy conversion (E ⋅ J > 2 nW/m3) at this structure [ABSTRACT FROM AUTHOR]

Starting in the evening of 10 May 2024 the Earth's magnetosphere was hit by the coronal mass ejections (CMEs) creating the largest geomagnetic storm in ∼ ${\sim} $20 years. The CME encounter was characterized by variations of plasma number density and magnetic field. Here, I present the ARTEMIS observations at the lunar orbit during this event. The IMF bz ${b}_{z}$ ranged from −60 to +40 nT both with ∼ ${\sim} $hour to minutes periodicity with plasma jets propagating in ±zGSE $\pm {z}_{\mathit{GSE}}$‐direction within multi‐scale wave structures. Similar signature has been recently reported at the magnetopause by MMS spacecraft (Li et al., 2023, https://doi.org/10.1029/2023GL105539; Nykyri, 2024, https://doi.org/10.1029/2024GL108605) during a strongly southward IMF. Here, I show that the CME boundaries were KH unstable leading to multi‐scale density and magnetic field fluctuations including reconnection jets. The wavelengths varied from ∼ ${\sim} $60 to 270 RE ${R}_{E}$, suggesting that the magnetosphere was periodically exposed to successive intervals of strongly northward and southward IMF leading to enhanced mass and magnetic flux loading. Plain Language Summary: Coronal mass ejections (CMEs) are giant explosions of plasma and magnetic field from the Sun which can produce beautiful Auroras, but also destroy our satellites, power delivery networks, and avionics systems. The seriousness of the storm depends on the pre‐existing conditions of the magnetosphere, the strength and orientation of the magnetic field within the CME structure, its size and speed which drives its duration, as well as the properties of the plasma within it. In this paper, I discuss and analyze the CME observations during the recent Mother's day storm (started on 10 May 2024) using the ARTEMIS spacecraft data at the lunar orbit. During the CME encounter, the SC were exposed to periodic north‐south‐variations of the magnetic field orientation and plasma density which allowed the Earth's magnetosphere to be successively filled with plasma, and magnetic flux likely enabling its effective acceleration in large‐quantities. I show that these periodic variations were produced by giant ∼ ${\sim} $ 60–270 RE ${R}_{E}$ waves at the boundary of the CMEs, such that the entire Earth's magnetosphere was surfing the crests and troughs of these waves, and absorbing the kinetic and magnetic energy from the solar wind. Key Points: Velocity shear at the boundary of a coronal mass ejection (CME) ejecta created Kelvin‐Helmholtz Instability (KHI) ∼ ${\sim} $7 million km upstream the Earth‐Sun L‐1 pointKHI generated multi‐scale density and IMF bz ${b}_{z}$ fluctuations from −60 to +40 nT at the boundary layers of the CME ejecta encountersKH wavelengths varied from ∼ ${\sim} $60 to ∼ ${\sim} $270 RE ${R}_{E}$ implying periodic and successive mass and magnetic flux loading of the magnetosphere system [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]

It is commonly believed that because of the direct solar wind interaction with the Martian atmosphere/ionosphere, the planet could have lost a significant part of its atmosphere. Closed field lines of the crustal magnetic field can weaken a transport of the ionospheric ions to the tail. Reconnection of the interplanetary magnetic field lines draping around Mars and the crustal magnetic field can also lead to a presense of sunward fluxes of planetary ions that might affect the total ion loss. The LatHyS (LATMOS Hybrid Simulation) three‐dimensional multispecies hybrid model is used here to characterize sunward fluxes of O+ ions and the magnetic field topology at Mars. It is shown that although reconnection between the interplanetary magnetic field (IMF) and the crustal magnetic fields strongly modifies the field topology, then sunward ion fluxes are rather small and do not significantly change the total ion loss. Plain Language Summary: Although Mars has no a global intrinsic magnetic field and solar wind interacts directly with the planetary atmosphere/ionosphere, the existence of strong but localized crustal magnetic field modifies the field topology around Mars. As a result, the Martian magnetosphere contains elements of the intrinsic and the induced magnetospheres. Reconnection between the interplanetary magnetic field and the crustal magnetic field can generate the plasma flows toward the planet and decrease the ionospheric losses, which is very important for the evolution of the Mars atmosphere/ionosphere. We have performed the numerical simulations of these potential effects and shown that the sunward ion fluxes are significantly less than the losses induced by the solar wind impact on the Martian ionosphere. Key Points: Hybrid simulations show a drastic change of the field topology at altitudes less than ∼1,000 km due to crustal field sourcesAlthough the magnetic field topology is modified, the sunward fluxes do not essentially affect the total ion lossSunward fluxes of oxygen ions in the tail vary between ∼5% and ∼20% compared to the anti‐sunward fluxes [ABSTRACT FROM AUTHOR]

Magnetic reconnection is a fundamental process known to play a crucial role in electron acceleration and heating, however, the mechanism of electron energization during reconnection is still not fully understood. This study introduces a novel electron acceleration mechanism in which electrons can be accelerated by secondary reconnection in the separatrix region. The secondary reconnection occurs in a thin current sheet resulted from the shear of the out‐of‐plane Hall magnetic fields of the primary magnetopause reconnection. It results in the intense electron energy fluxes toward the primary X‐line. This mechanism will likely be an important piece in the puzzle of particle acceleration by reconnection. Plain Language Summary: Magnetic reconnection is a fundamental process that plays a critical role in electron acceleration and heating. The separatrix region of magnetic reconnection, which distinguishes the inflow and outflow regions, is a crucial area in the particle acceleration of the reconnection process. However, previous studies mainly focused on the electron acceleration mechanism in the separatrix region under two‐dimensional reconnection, without considering the influence of the three‐dimensional structures. This paper reports, for the first time, the secondary reconnection occurring in the opposite Hall magnetic field in the three‐dimensional separatrix region of magnetopause primary reconnection. This secondary reconnection can accelerate and heat the inflow electrons of the primary reconnection, which provides important clues on how the particles are accelerated and heated by reconnection. Key Points: Secondary reconnection occurs between Hall magnetic fields in the separatrix region of the primary magnetopause reconnectionIntense electron enthalpy fluxes are injected toward the primary X‐line along the separatrixElectrons are accelerated by the secondary reconnection before being injected into the primary X‐line for further energization [ABSTRACT FROM AUTHOR]

The long‐standing "energy crisis" at the giant planets refers to the anomalous heating of planetary thermospheres compared to the available energy from solar irradiance. The coupling between planetary magnetospheres and their upper atmospheres is thought to address these crises, though the sources and pathways of energy transport have not been fully explored at each system. In particular, the total available energy from the upstream solar wind at each planet has not been comprehensively quantified. Here we apply recently developed models of energy conversion by magnetic reconnection and the Kelvin‐Helmholtz instability to each of the Giant Planets, providing estimates of the average external energy inputs for each system between 1985 and 2020. We find that external energy associated with solar‐wind‐magnetospheric coupling significantly exceeds that from solar extreme ultraviolet photons. While internal energy sources are known to dominate at Jupiter and Saturn, external sources may be significant at Uranus and Neptune. Plain Language Summary: The upper atmospheres of Jupiter, Saturn, Uranus, and Neptune are all hotter than would be predicted by their exposure to sunlight alone. The space plasma environment around each planet provides an additional reservoir of energy that can be used to provide this heating. Here we quantify the average energy input to each planetary system due to variation of the photons and plasmas emitted from the Sun. We find that the interaction between a planetary magnetic field and the solar interplanetary magnetic field provides a strong source of external energy at each of the planets, on average significantly more than that of light from the Sun. Key Points: Solar wind‐magnetospheric‐coupling provides higher energy input than solar extreme ultraviolet at the giant planetsSolar activity drives solar‐wind‐magnetospheric coupling much more strongly than planetary seasonThe solar wind may drive the energy input to the upper atmospheres at Uranus and Neptune [ABSTRACT FROM AUTHOR]

Energy conversion between the fields and the particles occurs through various physical processes within space environments. Magnetic reconnection stands out as one such process capable of rapidly and massively releasing energy. The high‐speed outflow jets produced by reconnection can induce turbulence characterized by intermittent structures. In this study, we investigate the impact of guide field on the energy conversion associated with the magnetic topologies within these structures during reconnection. Utilizing both particle‐in‐cell simulations and observations from the Magnetospheric Multiscale mission, our findings suggest that a larger guide field present during reconnection leads to increased energy conversion as well as the generation of O‐type topology structures within the turbulent outflow. Our results provide significant evidence on the relationships between energy conversion and magnetic topologies within turbulent outflow of reconnection and the guide field conditions. Plain Language Summary: In space environments, various physical processes involve the conversion of energy between magnetic fields and particles. One such process is magnetic reconnection, which can rapidly release a large amount of energy. During magnetic reconnection, high‐speed outflow jets are generated, leading to the formation of turbulent structures. In our study, we investigate how the presence of a guide field affects the energy conversion process and the resulting magnetic topologies within these turbulent structures during reconnection events. Using both particle‐in‐cell simulations and observations from the Magnetospheric Multiscale mission, we explore the impact of guide fields on energy conversion and magnetic topologies. Our findings indicate that a larger guide field present during reconnection leads to increased energy conversion and the generation of specific magnetic topology structures known as O‐type topologies within the turbulent outflow. These results provide significant insights into the complex relationships between energy conversion processes, magnetic topologies, and guide field conditions during magnetic reconnection events in space. Understanding these relationships is crucial for advancing our knowledge of fundamental physical processes occurring in space environments. Key Points: Magnetic topology in the turbulent reconnection outflow is investigated through both Magnetospheric Multiscale (MMS) observations and particle‐in‐cell (PIC) simulationsA larger guide field can promote the generation of O‐type topology in the turbulent outflow of the reconnectionHigher energy conversion is contributed by those O‐type topologies in the presence of a larger guide field [ABSTRACT FROM AUTHOR]

While Mars lacks a global intrinsic magnetic field, it does exhibit crustal magnetic anomalies (mostly in its Southern Hemisphere). These crustal magnetic anomalies directly interact with solar wind, which forms a mini‐magnetosphere and a region denoted the mini‐magnetopause. Using magnetic field and plasma measurements from the Mars Atmosphere and Volatile Evolution, we report a novel case of magnetic reconnection at the Martian mini‐magnetopause. In this process, protons and oxygen ions from the Martian atmosphere were accelerated during reconnection and likely escaped along the outflow direction. Magnetic reconnection may occur between the interplanetary magnetic field and crustal magnetic fields at the Martian mini‐magnetopause, which contributes to planetary ion escape, solar wind entering the mini‐magnetosphere and the evolution of magnetic topology in the dayside Martian mini‐magnetosphere. Plain Language Summary: While Mars lacks a global intrinsic magnetic field, it does exhibit crustal magnetic anomalies. The solar wind from the sun accompanied by interplanetary magnetic field (IMF) directly interacts with this crustal magnetic field, similar to what occurs on Earth, albeit at a smaller scale. The boundary between the crustal field on Mars and the IMF is called the mini‐magnetopause. Magnetic reconnection is a fundamental process in astrophysical and space plasmas that can change the topology of magnetic field and effectively convert magnetic energy into thermal and kinetic energy. Using magnetic field and plasma measurements from the Mars Atmosphere and Volatile Evolution missions, we report direction observations of magnetic reconnection at the Martian mini‐magnetopause. Through magnetic reconnection at the mini‐magnetopause, the IMF reconnects with the magnetic field from the crustal field, forming new magnetic field lines that channel solar wind to enter the Martian atmosphere and planetary plasmas to escape. Key Points: Magnetic reconnection at the Martian mini‐magnetopause is reported for the first timeProton and oxygen ions from the mini‐magnetosphere are accelerated during magnetic reconnectionMagnetic reconnection at the mini‐magnetopause could cause solar wind to enter the mini‐magnetosphere [ABSTRACT FROM AUTHOR]

Using high‐resolution data from the Magnetospheric Multiscale mission, an electron‐only reconnection current sheet is found between two successive dipolarization fronts (DFs). The electron‐only reconnection occurs between the northward component of the magnetic field of the flux pileup region (FPR) of the first DF (DF1) and the southward component of the magnetic dip of the second DF (DF2). The faster DF2 compresses the FPR of DF1, which constitutes an anti‐parallel topology and reduces the thickness of the current sheet. Further analysis shows that the current sheet is unstable to the electron tearing instability, which may power the onset of the reconnection. Our results suggest that these two DFs may merge into one by the reconnection, which sheds light on the evolution of DFs during their earthward propagation. Plain Language Summary: Magnetic reconnection, releasing magnetic energy and energizing plasmas, are believed to be responsible for the explosive phenomena in space. Though reconnection has been investigated for decades, the onset of reconnection is elusive. Dipolarization fronts (DFs), important carriers in the transportation of mass, magnetic flux, and energy in the magnetotail, can be generated by reconnections and will integrate into the geomagnetic field at last. The generation of DFs and dynamics at DFs are thoroughly probed by simulations and observations. However, the evolution of DFs during their earthward propagation is rarely inspected. In this work, we present an observation of an electron‐only reconnection between two successive DFs. The latter DF compresses the former DF and reduces the thickness of the current sheet between them. Inside the reconnection current sheet, electron tearing instability is unstable, which may power the reconnection. By reconnection, these two DFs may merge. Our observations can improve our understanding of the evolution of DFs in the magnetotail. Key Points: An electron‐only reconnection current sheet is found between two dipolarization frontsThe current sheet is unstable to the electron tearing instabilityDF2 compresses DF1 and thins the current sheet, which may initiate electron tearing instability and trigger the reconnection [ABSTRACT FROM AUTHOR]

As the interplanetary magnetic field (IMF) carried by the solar wind encounters the martian atmosphere, it tends to pile up and drape around the planet, forming looping magnetic fields and inducing marsward ion flows on the nightside. Previous statistical observations revealed asymmetrical distribution features within this morphology; however, the underlying physical mechanism remains unclear. In this study, utilizing a three‐dimensional multi‐fluid magnetohydrodynamic simulation model, we successfully reproduce the asymmetrical distributions of the looping magnetic fields and corresponding marsward flows on the martian nightside. Analyzing the magnetic forces resulting from the bending of the IMF over the polar area, we find that the asymmetry is guided by the orientation of the solar wind motional electric field (ESW). A higher solar wind velocity leads to enhanced magnetic forces, resulting in more tightly wrapped magnetic fields with an increased efficiency in accelerating flows as they approach closer to Mars. Plain Language Summary: As incident solar wind interacts with Mars, the entrained interplanetary magnetic field drapes and stretches around the planet. The draped fields are orientated in opposite directions on the east and west sides of Mars, resulting in magnetic reconnection, the formation of looping magnetic fields and induced marsward plasma flows on the nightside. Statistical observations suggest an asymmetric distribution of these structures, however, the underlying physical mechanisms for this asymmetry have not been determined due to limited spatial coverage offered by the single spacecraft investigations. In this study, by taking advantage of a Hall‐MHD model, we have successfully reproduced the asymmetrical distributions and elucidated the underlying mechanisms governing these morphologies. Simulation results demonstrate that magnetic forces tend to emerge around the polar region, which are determined by the orientation of the ESW, shifting the plasma flows and magnetic fields in the direction opposite to the motional electric field. A higher solar wind velocity condition will induce amplified magnetic forces, resulting in more tightly wrapped magnetic fields and an increase in the velocity of marsward flows closer to the martian nightside. These findings provide valuable insights into the influence of the ESW and solar wind velocity on the martian induced magnetosphere. Key Points: The asymmetrical distributions of looping magnetic fields and associated marsward flows can be well reproduced by a multi‐fluid magnetohydrodynamic (MHD) modelThe impacts of the motional electric field direction and the solar wind velocity on the asymmetries are investigated, respectivelyMagnetic forces shift the magnetic fields and marsward flows toward the direction opposite to the motional electric field [ABSTRACT FROM AUTHOR]

The MMS satellites traversed a ∼6 di‐wide and ∼500 km/s southward reconnection exhaust at the dayside magnetopause on 6 December 2015 and ∼29 di from the associated X‐line region. A narrow ∼0.26–0.34 di layer of enhanced ±3.5 nW/m3 oscillating energy conversion perpendicular to the magnetic field resides in this exhaust. It contained two regions of diverging in‐plane electric fields in general agreement with two clockwise electron flow vortices and a proposed increase of the electron vorticity ∇ × Ve. The layer developed sunward of a unipolar Hall magnetic field for a duskward BM/BL ∼ 0.9 guide field. Each electron flow vortex supported a local ∆BM ∼ 10 nT strengthening of this Hall field. The presence of this electron‐scale layer in a southward exhaust for a duskward guide field is consistent with a two‐dimensional simulation of a similar structure that evolved from an X‐line into a northward exhaust for a similar strength dawnward guide field. Plain Language Summary: Magnetic reconnection is a critical process that drives large‐scale plasma convection in the Earth's magnetosphere. In this letter, we report new direct MMS observations for the presence of two electron flow vortices within a sub‐ion scale energy conversion channel that resides in a dayside magnetopause reconnection exhaust. Each of the two electron‐scale flow vortices is shown to contribute a significant fraction toward the large‐scale Hall magnetic field. Key Points: Electron‐scale 0.3 di layer of oscillating energy conversion and electron vorticity detected in 6 di wide reconnection jet 30 di from EDRTwo regions of in‐plane diverging electric field in energy conversion layer consistent with two measured clockwise electron flow vorticesOut‐of‐plane magnetic field increased ∼10 nT from each passing electron vortex immediately sunward of 50 nT unipolar Hall magnetic field [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]

Using a two‐way coupled magnetohydrodynamics with embedded kinetic physics model, we perform a substorm event simulation to study electron velocity distribution functions (VDFs) evolution associated with Bursty Bulk Flows (BBFs). The substorm was observed by Magnetospheric Multiscale satellite on 16 May 2017. The simulated BBF macroscopic characteristics and electron VDFs agree well with observations. The VDFs from the BBF tail to its dipolarization front (DF) during its earthward propagation are revealed and they show clear energization and heating. The electron pitch angle distributions (PADs) at the DF are also tracked, which show interesting energy dependent features. Lower energy electrons develop a "two‐hump" PAD while the higher energy ones show persist "pancake" distribution. Our study reveals for the first time the evolution of electron VDFs as a BBF moves earthward using a two‐way coupled global and kinetic model, and provides valuable contextual understanding for the interpretation of satellite observations. Plain Language Summary: Bursty bulk flows (BBFs) are identified as the fast earthward‐propagating flows from magnetic reconnection in the Earth's magnetotail. BBFs are related to particle energization and heating processes as reported by satellite observations. For the first time, we use a novel numerical model that simulates kinetic physics directly in a global model. The electron velocity distribution functions extracted from multiple locations associated with BBF show good agreements with the satellite in situ observations. The energization and heating of the electrons associated with BBF and their energy‐dependent pitch angle distributions are revealed. Key Points: For the first time, we simulate the bursty bulk flow (BBF) events with kinetic physics embedded in a global magnetosphere modelThe electron velocity distribution functions exhibit different anisotropy features at different locations of the BBFEnergy dependent electron pitch angle distribution evolutions are identified in the simulation [ABSTRACT FROM AUTHOR]

Abstract Starting in the evening of 10 May 2024 the Earth's magnetosphere was hit by the coronal mass ejections (CMEs) creating the largest geomagnetic storm in ∼20 years. The CME encounter was characterized by variations of plasma number density and magnetic field. Here, I present the ARTEMIS observations at the lunar orbit during this event. The IMF bz ranged from −60 to +40 nT both with ∼hour to minutes periodicity with plasma jets propagating in ±zGSE‐direction within multi‐scale wave structures. Similar signature has been recently reported at the magnetopause by MMS spacecraft (Li et al., 2023, https://doi.org/10.1029/2023GL105539; Nykyri, 2024, https://doi.org/10.1029/2024GL108605) during a strongly southward IMF. Here, I show that the CME boundaries were KH unstable leading to multi‐scale density and magnetic field fluctuations including reconnection jets. The wavelengths varied from ∼60 to 270 RE, suggesting that the magnetosphere was periodically exposed to successive intervals of strongly northward and southward IMF leading to enhanced mass and magnetic flux loading.

An earlier model of the electron distribution function accounts for the pressure anisotropy that develops in the inflow regions during anti‐parallel magnetic reconnection. However, the model is not applicable to the electron diffusion region (EDR), where the electron magnetic moments break as an adiabatic invariant. The earlier model is here generalized through the use of the current‐sheet adiabatic invariant of a 1D current layer, to become applicable also to the EDR. The new generalized model reproduces the main features of the EDR and its vicinity observed in a fully kinetic simulation, formally proving the 1D equilibrium relationship between the upstream electron pressure anisotropy and the EDR electron jets. Plain Language Summary: Ever since 1953 when Dungey introduced the concept of magnetic reconnection in the Earth's magnetotail, the process has been investigated as the potential cause of the Aurora phenomenon. During reconnection the magnetic field lines break and reform with changed connectivity as they pass through a small electron diffusion region (EDR). In the magnetotail the EDRs responsible for the Aurora often forms about 20 Earths radii away from Earth, spectacularly breaking the standard rules of plasma physics in ways not fully understood. In the present letter we show how the structure of the EDR can largely be accounted for through a relatively simple kinetic model. The model relies on an adiabatic invariant of the electron motion perpendicular to the magnetotail current sheet, and it accounts for the electron pressure anisotropy which builds at the edge of the EDR. In turn, we show how the thermal forces associated with this pressure anisotropy are responsible for driving the strong electron jets observed within in the EDR. The model is validated against a state‐of‐the‐art supercomputer simulation of the reconnection process. Key Points: During anti‐parallel magnetic reconnection the electron diffusion region (EDR) has a largely 1D structureThe cross‐section of the 1D structure is governed by the invariance of the electron current sheet action integral, Jz=∮vzdz ${\mathcal{J}}_{z}=\oint {v}_{z}dz$Electron pressure anisotropy forms upstream of the EDR, couples to the Speiser orbits, and drives the electron jets of the EDR [ABSTRACT FROM AUTHOR]

The secondary processes driven by the velocity shear driven Kelvin‐Helmholtz Instability (KHI) in the magnetized plasmas have been shown to be important in producing plasma transport and heating from the shocked solar wind into the Earth's magnetosphere (MSP). The plasma transport into the MSP due to KHI has been shown to be strongest during northward interplanetary magnetic field (IMF) via KHI driven low‐ and mid‐latitude reconnection process. In a recent article, Li et al. (2023), https://doi.org/10.1029/2023gl105539 show Magnetosphere Multi‐Scale (MMS) spacecraft observations of multiple, Alfvénic reconnection jets during southward IMF at the dawn‐side MSP flank. The quasi‐periodic oscillations in plasma parameters and compressed, ion‐scale current sheets were strongly indicative of the MMS crossing regions of MSP‐like and magnetosheath‐like plasma within Kelvin‐Helmholtz waves. In this brief commentary, the importance of this new discovery for magnetospheric and solar wind dynamics is discussed. Plain Language Summary: Earth's magnetic field serves as a protective barrier, forming a magnetic bubble known as the magnetosphere in the solar wind. Acting like a shield, the magnetopause is a crucial surface that delineates the separation between the solar wind and the plasma enveloped within Earth's magnetosphere. However, this shield is not impervious; a phenomenon called magnetic reconnection can compromise it, permitting direct access for solar wind plasma. This process is particularly effective when the interplanetary magnetic field (IMF) carried by the solar wind opposes Earth's magnetic field direction, a configuration known as "southward" IMF. Under these conditions, the Earth's magnetic field opens at the dayside, facilitating the accumulation of mass, momentum, and energy into the night‐side magnetotail. In a recent discovery, NASA's four Magnetosphere Multiscale spacecraft revealed that magnetic reconnection can also occur during southward IMF at the tail flanks of our magnetic bubble. This reconnection, strongly driven by colossal waves with wavelengths of 56,000 km (Kelvin‐Helmholtz waves) creates portals in our magnetic shield, enabling both the escape and entry of particles. In this brief commentary, the importance of this finding is discussed, both for magnetospheric and solar wind dynamics. Key Points: Kelvin‐Helmholtz Instability (KHI) can generate compressed current sheets, effectively driving magnetic reconnection at flanks during southward interplanetary magnetic fieldKHI driven reconnection can aid energetic particle escape from the magnetosphereKHI driven reconnection may also play role for energetic particle dynamics within solar wind structures [ABSTRACT FROM AUTHOR]

Recent MMS observations have discovered electron‐scale super‐thin current sheets (STCSs) with a partial electron demagnetization, which distinguishes them from the ion‐scale TCSs traditionally observed by the Cluster mission. Our investigation focuses on the dynamics of STCSs and reveals new aspects influencing their stability. We use the earlier proposed 1D collisionless self‐consistent equilibrium STCS model and show that the free parameters of this model, such as the relative part of demagnetized electrons, their flow velocity and the pressure anisotropy of magnetized electron population, can contribute to the development of tearing instability. With the growth of these parameters, the STCS becomes thinner, which leads to the accumulation excess of a free energy. Stabilizing energy decreases due to the increase of a relative part of demagnetized electrons. Thus, demagnetized electrons in STCSs can provide the development of fast and short‐wavelength electron tearing modes. Plain Language Summary: Recent MMS observations in space plasma have discovered extremely thin current sheets having the transverse electron scales. These sheets are different from the thicker current sheets usually observed by the Cluster mission. The electrons in these sheets are partially demagnetized, that is, they are not affected by magnetic fields. The presence of demagnetized electrons can lead to the development of a fast tearing mode with the shorter wavelengths in comparison with corresponding modes observed in the thicker current configurations. Our investigation focuses on the understanding of the dynamics of these super‐thin current sheets and the identification of factors that influence their stability. Key Points: Demagnetized electrons supporting STCSs can initiate the fast electron tearing instability at short wavelengthsFast growth of small‐scale magnetic perturbation results in the formation of magnetic islands, that is, plasmoidsDevelopment of fast tearing mode is followed by strong inductive electric fields [ABSTRACT FROM AUTHOR]

Magnetic flux ropes are ubiquitous in various space environments, including the solar corona, interplanetary solar wind, and planetary magnetospheres. When these flux ropes intertwine, magnetic reconnection may occur at the interface, forming disentangled new ropes. Some of these newly formed ropes contain reversed helicity along their axes, diverging from the traditional flux rope model. We introduce new observations and interpretations of these newly formed flux ropes from existing Hall Magnetohydrodynamics model results. We first examine the time‐varying local magnetic field direction at the impact interface to assess the likelihood of reconnection. Then we investigate the electric current system to describe the evolution of these structures, which potentially accelerate particles and heat the plasma. This study offers novel insights into the dynamics of space plasmas and suggests a potential solar wind heating source, calling for further synthetic observations. Plain Language Summary: This research examines a special type of systematically twisted magnetic fields, known as flux ropes, in the sun's atmosphere, the solar wind, and near planets. Built on earlier model results, this examination brings a new understanding of how these special flux ropes emerge from collisions between flux ropes. These results use a commonly used simulation tool for large‐scale plasmas to study the new ropes formed after two flux ropes are pushed toward each other long enough. In some cases, each of the new ropes may have opposite twists between their two ends. We then examine how the magnetic field changes across the interface during the evolution. Changes in electric currents found in these situations further explain the formation and evolution of the new rope pairs. This examination helps to better understand the behavior of space plasma's heating of the solar wind and its control of space weather. Key Points: We examine the interaction of magnetic flux ropes that consist of opposite helicity along their axes using numerical simulationsWe present the evolution of their current system, from which we anticipate a significant amount of energy releaseThese structures could be present on the solar surface, in the solar wind, and in magnetospheres [ABSTRACT FROM AUTHOR]

Dipolarization fronts (DFs) are widely believed to host energy conversion processes. However, which mechanism is responsible for the energy conversion is still obscure. Using data from the Magnetospheric Multiscale mission, a current sheet is observed at a DF. This current sheet is caused by interchange instability bending the edge of the DF. Inside the current sheet, Hall electromagnetic field, super Alfvénic electron jets, demagnetization of ions and electrons, strong energy conversion, and steady ion flow and temperature are observed, indicating an electron‐only reconnection at the DF. The duskward plasma flow, which may be deflected by the DF, compresses the bent edges of the DF. As a result, the width of the current sheet between two adjacent bent edges of the DF reduces, and then reconnection begins. Our observations give direct evidence that magnetic reconnection results in energy conversion at a DF. Plain Language Summary: Magnetic reconnection is an explosive phenomenon in space, which can rapidly convert energy from magnetic field to particles. Dipolarization fronts are essential carriers of mass and energy from the magnetotail to the Earth. Strong energy conversion, considered to be even more significant than magnetic reconnection, is usually observed at dipolarization fronts. However, the specific mechanism responsible for the energy conversion at a dipolarization front is elusive. Using data from the Magnetospheric Multiscale mission, we present direct evidence of magnetic reconnection at a dipolarization front, leading to strong energy conversion. The reconnection occurs in the current sheet at the dipolarization front. The duskward diverted flow compresses the bent dipolarization front induced by interchange instability, resulting in reconnection. Key Points: A current sheet with strong energy conversion is found at a DFThe strong energy conversion at this DF is mainly caused by the magnetic reconnectionThe duskward diverted flow compresses the bent DF caused by interchange instability, leading to the reconnection [ABSTRACT FROM AUTHOR]

When the solar wind speed falls below the local Alfvén speed, the magnetotail transforms into an Alfvén wing configuration. A Grid Agnostic Magnetohydrodynamics for Extended Research Applications (GAMERA) simulation of Earth's magnetosphere using solar wind parameters from the 24 April 2023 sub‐Alfvénic interval is examined to reveal modifications of Dungey‐type magnetotail reconnection during sustained sub‐Alfvénic solar wind. The simulation shows new magnetospheric flux is generated via reconnection between polar cap field lines from the northern and southern hemisphere, similar to Dungey‐type magnetotail reconnection between lobe field lines mapping to opposite hemispheres. The key feature setting the Alfvén wing reconnection apart from the typical Dungey‐type is that the majority of new magnetospheric flux is added to the polar cap at local times 1–3 (21‐23) in the northern (southern) hemisphere. During most of the sub‐Alfvénic interval, reconnection mapping to midnight in the polar cap generates relatively little new magnetospheric flux. Plain Language Summary: Similar to how a shock wave forms around a supersonic plane, the supersonic plasma emanating from the sun forms a shock wave around Earth. However, the speed of sound through the plasma depends on different parameters that vary substantially based on the origin and evolution of solar material flowing into interplanetary space. In some coronal mass ejections, the characteristics of the plasma are such that the flow is sub‐sonic, leaving the magnetosphere in a unique state. Determining whether there are any space weather impacts associated with the sub‐sonic flow has been difficult due to lack of observations, but a recent event has ignited interest. This study examines the global structure and dynamics of the magnetosphere in a simulation representative of the sub‐sonic flow interval of the April 2023 geomagnetic storm. Key Points: On 24 April 2023, Earth's magnetosphere experienced an interval of sustained sub‐Alfvénic solar wind drivingSub‐Alfvénic driving suppresses typical Dungey‐type magnetotail reconnection but polar cap expansion is still limitedGlobal simulations have strong Earthward flows localized ∼10 RE tailward of theterminator, where most new magnetospheric flux is generated [ABSTRACT FROM AUTHOR]

An ongoing magnetic reconnection event was detected in the Mercury's high latitude magnetopause during a northward interplanetary magnetic field. The reconnection X‐line region was revealed in the Mercury's magnetopause based on the encountered flux ropes ejected away from this region both planetward and tailward. A series of magnetic flux ropes, known as flux transfer event shower were observed tailward of this X‐line region. These flux ropes were probably expanding and deflected as they were ejected away tailward from the X‐line region. Large‐amplitude variations in all three components of the magnetic field and a few small‐scale flux ropes were observed inside the X‐line region, which could be the seed of the flux rope shower at the magnetopause. The observations suggest that magnetic reconnection is highly dynamic and persistent in Mercury's magnetosphere. Plain Language Summary: Magnetic reconnection has been regarded as the most important process for dynamics of the Mercury's magnetosphere and for the interaction between the solar wind and the Mercury's magnetosphere also. Although magnetic flux ropes and flux transfer events (FTEs) resulting from magnetic reconnection have been extensively observed in the Mercury's magnetosphere, the key region of magnetic reconnection, namely the X‐line region, has never been reported so far by the spacecraft. Here, we present the first evidence of the reconnection X‐line region in the Mercury's magnetosphere. A few small‐scale magnetic flux ropes are observed inside the reconnection X‐line region, which could be the seed of the observed magnetic FTE shower. Furthermore, the evolution of these flux ropes is addressed also based on the spacecraft observations. Key Points: A reconnection X‐line region is first observed in the Mercury's magnetopause during the northward interplanetary magnetic fieldThe small‐scale magnetic flux ropes in the X‐line region could be the seed of the flux transfer event showerThe flux ropes probably expand and is deflected after they are ejected away from the X‐line region [ABSTRACT FROM AUTHOR]

Magnetic reconnection is the physical process that converts the energy from the fields to the plasmas in space, astrophysical and laboratory plasmas. The Reconnection front (RF) is the structure generated in the reconnection outflow region and participates in the energy release budget. Here, we first report a novel crater structure of magnetic field behind the RF, which is well supported by both the in‐situ observations from the Magnetospheric Multiscale mission and kinetic particle‐in‐cell simulations. The theoretical explanations from the simulations suggests that the formation of the crater structure is possibly due to that high‐speed outflow electron jet from inner electron diffusion region constantly strikes the RF. From another perspective, the crater structure is the continuous impact of the electron jet. Our results can establish a new understanding of the RF and energy conversion during magnetic reconnection. Plain Language Summary: Magnetic reconnection is a natural process in space environments, astrophysical settings, and laboratories, where energy from magnetic fields is transformed into the energy of various particles. One crucial structure in this process is called the reconnection front (RF), which plays a big role in how energy is released. In our study, we have discovered something interesting: a unique crater‐like structure behind the RF. We found evidence for this in observations from the Magnetospheric Multiscale mission and computer simulations that study the behavior of particles in magnetic reconnection. Our simulations suggest that this crater shape happens because electrons have the high‐speed outflow and form current jets. It is like the electrons poured out from the inner electron diffusion region, hitting a speed bump. Another way to think about it is that this crater is formed by the continuous impact of fast‐outflowing electron jets. Understanding this crater structure helps us better grasp how the RF works and how energy changes during magnetic reconnection. Our research finds and tries to explain a new piece of the puzzle in understanding the mysteries of space and plasmas in the magnetic reconnection process. Key Points: A novel crater structure is first verified behind the Reconnection front (RF) by both Magnetospheric Multiscale observations and particle‐in‐cell simulationsThe formation of the crater structure appears to be associated with the high‐speed electron jets from inner electron diffusion regionA possible scenario that electron outflow constantly strikes the RF and then causes the formation of the crater structure [ABSTRACT FROM AUTHOR]

Abstract 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.

The Martian magnetotail exhibits a highly twisted configuration, shifting in response to changes in polarity of the interplanetary magnetic fields (IMF) dawn-dusk (B Y) component. Here, we analyze ∼6000 MAVEN orbits to quantify the degree of magnetotail twisting (θ Twist) and assess variations as a function of (a) strong planetary crustal field location, (b) Mars season, and (c) downtail distance. The results demonstrate that θ Twist is larger for a duskward (+B Y) IMF orientation a majority of the time. This preference is likely due to the local orientation of crustal magnetic fields across the surface of Mars, where a +B Y IMF orientation presents ideal conditions for magnetic reconnection to occur. Additionally, we observe an increase in θ Twist with downtail distance, similar to Earths magnetotail. These findings suggest that coupling between the IMF and moderate-to-weak crustal field regions may play a major role in determining the magnetospheric structure at Mars.

Flux transfer events (FTEs) are transient magnetic flux ropes at Earth's dayside magnetopause formed due to magnetic reconnection. As they move across the magnetopause surface, they can generate disturbances in the ultralow frequency (ULF) range, which then propagate into the magnetosphere. This study provides evidence of ULF waves in the Pc2 wave frequency range (>0.1 Hz) caused by FTEs during dayside reconnection using a global 3D hybrid‐Vlasov simulation (Vlasiator). These waves resulted from FTE formation and propagation at the magnetopause are particularly associated with large, rapidly moving FTEs. The wave power is stronger in the morning than afternoon, showing local time asymmetry. In the pre and postnoon equatorial regions, significant poloidal and toroidal components are present alongside the compressional component. The noon sector, with fewer FTEs, has lower wave power and limited magnetospheric propagation. Plain Language Summary: The Earth's magnetosphere is a dynamic region shaped by the interplay between the solar wind and Earth's magnetic field. This interaction occurs at the boundary of the magnetosphere (magnetopause) through a process known as magnetic reconnection, giving rise to Flux Transfer Events (FTEs), which are magnetic structures that carry flux and energy into the magnetosphere. These FTEs form either in sudden bursts, patchy patterns or in a continuous, and relatively stable way making the magnetopause surface dynamic. As the FTEs move along the boundary of the magnetosphere, they create compressed regions and lead to wave generation that can extend into the magnetosphere. The study uses an advanced 3D hybrid‐Vlasov simulation model to analyze waves originated from FTE formation and propagation at the magnetopause. We find that rapidly moving and large FTEs have a significant impact on the magnetopause, leading to the generation of ULF waves with frequency above 0.1 Hz. This shows first direct evidence supporting previous theoretical speculations regarding the ability of FTEs to generate waves near the magnetopause. Key Points: Dayside Pc2 waves (>0.1 Hz) have been detected in a 3D hybrid‐Vlasov simulationThese waves exhibit lower intensity within the magnetosphere at noon, compared to the prenoon and postnoon sectorsPc2 waves observed in the simulation are associated with largest and fast moving flux transfer events initiated by subsolar reconnection [ABSTRACT FROM AUTHOR]

Recent magnetospheric observations and three‐dimensional (3D) kinetic simulations have shown that plasma wave activities are significantly enhanced around the reconnection x‐line, implying that the reconnection process is fully 3D. However, how the turbulence affects the local reconnection process has been poorly understood so far. We find by means of large‐scale particle‐in‐cell simulation in 3D system that the local reconnection rate can be significantly enhanced, reaching 0.4, which is much larger than theoretical predictions for two‐dimensional (2D) reconnection. The large reconnection rate is associated with large energy conversion rate and strong electron acceleration. The enhancement of the reconnection rate is caused by local increases of electron momentum transport and pressure gradient force induced by turbulence, which can not occur in 2D system. The result is expected to give better interpretations to in‐situ satellite observations where magnetic reconnection proceeds in 3D system. Plain Language Summary: Magnetic reconnection is an important process in space physics to convert the magnetic field energy into particle kinetic energy. In this study, we investigate reconnection rate, a physical quantity that measures the speed of magnetic reconnection by using fully kinetic simulation, in which both electrons and ions are particles. We find very fast local reconnection processes in three‐dimensional system that far exceeds expectation. It indicates that magnetic reconnection is a three‐dimensional process. The high reconnection rate comes from the electrons rather than ions. And the main reason is the increasing of electron momentum transport and pressure gradient caused by strong turbulence, leading to a strong magnetic reconnection process in the current sheet. Key Points: Magnetic reconnection can be strongly intensified in turbulent current sheet with the local reconnection rate exceeding 0.4High reconnection rate is caused by local enhancements of electron momentum transport and pressure gradient force induced by turbulenceReconnection process is essentially 3D, suggesting that local satellite observations may be insufficient in capturing the global process [ABSTRACT FROM AUTHOR]

The Earth's magnetopause is an ion‐scale boundary that separates the magnetosphere from the shocked solar wind. At such boundary, energy‐conversion processes frequently occur. Previous studies suggested that such energy conversions are related to the magnetic reconnection process. Here, we report a new mechanism that the coaction between the twisted magnetic structure and lower‐hybrid waves can also drive energy conversion (J⋅ E, J is current density and E is electric field) at the magnetopause boundary layer, by using high‐resolution measurements of the four Magnetospheric Multiscale spacecraft. We find that such energy conversion is efficient (with magnitude up to 20 nW/m3) and is attributed to an intense current filament (j ≈ 3,800 nA/m2) and a fluctuating electric field driven by lower‐hybrid waves. With the help of the First‐Order Taylor Expansion method, we find that the intense current filament is driven by a twisted magnetic structure at electron scale. Our study improves the understanding of energy‐conversion processes at the Earth's magnetopause. Plain Language Summary: Solar wind‐magnetosphere coupling is a key process during the solar‐terrestrial energy chain and the space weather forecast. A significant amount of the solar wind energy is converted at the Earth's magnetopause, and thus, uncovering the mechanism of energy‐conversion processes is of key importance in understanding such a coupling process between solar wind and magnetosphere. Here, we report a new mechanism that the coaction between the twisted magnetic structure and fluctuating electric field can also drive energy conversion. It's found that the energy conversion is efficient and is attributed to an intense current filament driven by the twisted magnetic structure and a fluctuating electric field provided by lower‐hybrid waves. Key Points: An intense current filament (up to 3,800 nA/m2) accompanied by energy conversion (up to 20 nW/m3) are observed at the magnetopause boundary layerThe intense current filament is driven by an electron‐scale twisted magnetic structureThe energy conversion at the current filament is driven by the coaction between the twisted magnetic structure and the lower‐hybrid waves [ABSTRACT FROM AUTHOR]

Discrete aurora are sporadic emissions of light originating in Mars upper atmosphere. We report nadir imaging observations from MAVEN's Imaging UltraViolet Spectrograph which identify the conditions which trigger electron precipitation causing these events. Prior studies have shown that discrete aurora events in the strong crustal magnetic field region in the southern hemisphere are the brightest and most repeatable compared to events occurring outside the region. Our new data set offers a more complete and accurate characterization of aurora in this area. The region of strongest crustal fields is composed of two distinct magnetic regions, with magnetic fields in opposite directions; discrete aurora events trigger in one region after dusk and in the other before dawn. Magnetic reconnection in these two adjacent regions with the draped interplanetary field may open the crustal fields in these regions during opposing local times. Particle precipitation can then cause discrete aurora at the observed times and locations. Plain Language Summary: Mars has a surprising variety of types of aurora, all different from Earth's "northern lights." Mars lacks the familiar high‐latitude aurora because it no longer has the same kind of global magnetic field Earth does. This study examines "discrete aurora" events that occur in region in Mars southern hemisphere that has retained some of the ancient magnetic field. It takes the form of long arcades of magnetic loops that resemble a set of arches. As Mars rotates, these arcades are carried around the planet as the solar wind and its imbedded magnetic field are carried past the planet. We show that when conditions are favorable, the magnetic field locked in the solar wind can interact and "reconnect" with Mars magnetic loops, allowing energetic particles to spiral down the field lines into the atmosphere to cause discrete aurora. Key Points: New data confirm that Mars discrete aurora events occur most frequently near strong crustal fields and vary with local timeAuroral events in adjacent regions with opposite magnetic polarity occur before or after midnight depending on local magnetic field directionMagnetic reconnection between crustal fields and the draped interplanetary field appears to control regional and local time behavior [ABSTRACT FROM AUTHOR]

The generation of kinetic‐scale flux ropes (KSFRs) is closely related to magnetic reconnection. Both flux ropes and reconnection sites are detected in the magnetosheath and can impact the dynamics upstream of the magnetopause. In this study, using the Magnetospheric Multiscale satellite, 12,623 KSFRs with a scale <20 RCi are statistically studied in the Earth's dayside magnetosheath. It is found that they are mostly generated near the bow shock (BS), and propagate downstream in the magnetosheath. Their quantity significantly increases as the scale decreases, consistent with a flux rope coalescence model. Moreover, the solar wind parameters can control the occurrence rate of KSFRs. They are more easily generated at high Mach number, large proton density, and weak magnetic field strength of the solar wind, similar to the conditions that favor BS reconnection. Our study shows a close connection between KSFR generation and BS reconnection. Plain Language Summary: Kinetic‐scale flux ropes (KSFRs) exist widely in near‐earth space and play an important role in mass transport, energy conversion, and dissipation during magnetic field reconnection. The KSFR in the magnetosheath can be generated by reconnection in three regions: the magnetopause, the magnetosheath, and the BS. The spatial distribution of KSFRs can indirectly reflect the reconnection situation in the magnetosheath. We use various methods to select the KSFRs and study their spatial distribution and generation in the magnetosheath. Our results show that BS reconnection plays an important role in generating the KSFR in the magnetosheath. Key Points: Kinetic‐scale flux ropes observed in the magnetosheath are primarily generated near the bow shock (BS) and travel to downstream magnetosheathThe quantity of flux ropes significantly increases as their scale decreases, which is in accordance with the FR coalescence modelThe occurrence of flux ropes is influenced by solar wind parameters, and could strongly correlate with BS reconnection [ABSTRACT FROM AUTHOR]

Abstract Recent MMS observations have discovered electron‐scale super‐thin current sheets (STCSs) with a partial electron demagnetization, which distinguishes them from the ion‐scale TCSs traditionally observed by the Cluster mission. Our investigation focuses on the dynamics of STCSs and reveals new aspects influencing their stability. We use the earlier proposed 1D collisionless self‐consistent equilibrium STCS model and show that the free parameters of this model, such as the relative part of demagnetized electrons, their flow velocity and the pressure anisotropy of magnetized electron population, can contribute to the development of tearing instability. With the growth of these parameters, the STCS becomes thinner, which leads to the accumulation excess of a free energy. Stabilizing energy decreases due to the increase of a relative part of demagnetized electrons. Thus, demagnetized electrons in STCSs can provide the development of fast and short‐wavelength electron tearing modes.

Abstract The secondary processes driven by the velocity shear driven Kelvin‐Helmholtz Instability (KHI) in the magnetized plasmas have been shown to be important in producing plasma transport and heating from the shocked solar wind into the Earth's magnetosphere (MSP). The plasma transport into the MSP due to KHI has been shown to be strongest during northward interplanetary magnetic field (IMF) via KHI driven low‐ and mid‐latitude reconnection process. In a recent article, Li et al. (2023), https://doi.org/10.1029/2023gl105539 show Magnetosphere Multi‐Scale (MMS) spacecraft observations of multiple, Alfvénic reconnection jets during southward IMF at the dawn‐side MSP flank. The quasi‐periodic oscillations in plasma parameters and compressed, ion‐scale current sheets were strongly indicative of the MMS crossing regions of MSP‐like and magnetosheath‐like plasma within Kelvin‐Helmholtz waves. In this brief commentary, the importance of this new discovery for magnetospheric and solar wind dynamics is discussed.

Abstract An ongoing magnetic reconnection event was detected in the Mercury's high latitude magnetopause during a northward interplanetary magnetic field. The reconnection X‐line region was revealed in the Mercury's magnetopause based on the encountered flux ropes ejected away from this region both planetward and tailward. A series of magnetic flux ropes, known as flux transfer event shower were observed tailward of this X‐line region. These flux ropes were probably expanding and deflected as they were ejected away tailward from the X‐line region. Large‐amplitude variations in all three components of the magnetic field and a few small‐scale flux ropes were observed inside the X‐line region, which could be the seed of the flux rope shower at the magnetopause. The observations suggest that magnetic reconnection is highly dynamic and persistent in Mercury's magnetosphere.

Abstract Dipolarization fronts (DFs) are widely believed to host energy conversion processes. However, which mechanism is responsible for the energy conversion is still obscure. Using data from the Magnetospheric Multiscale mission, a current sheet is observed at a DF. This current sheet is caused by interchange instability bending the edge of the DF. Inside the current sheet, Hall electromagnetic field, super Alfvénic electron jets, demagnetization of ions and electrons, strong energy conversion, and steady ion flow and temperature are observed, indicating an electron‐only reconnection at the DF. The duskward plasma flow, which may be deflected by the DF, compresses the bent edges of the DF. As a result, the width of the current sheet between two adjacent bent edges of the DF reduces, and then reconnection begins. Our observations give direct evidence that magnetic reconnection results in energy conversion at a DF.

We report observations of reconnection exhausts in the Heliospheric Current Sheet (HCS) during Parker Solar Probe Encounters 08 and 07, at 16 R s and 20 R s , respectively. Heliospheric current sheet (HCS) reconnection accelerated protons to almost twice the solar wind speed and increased the proton core energy by a factor of ∼3, due to the Alfvén speed being comparable to the solar wind flow speed at these near-Sun distances. Furthermore, protons were energized to super-thermal energies. During E08, energized protons were found to have leaked out of the exhaust along separatrix field lines, appearing as field-aligned energetic proton beams in a broad region outside the HCS. Concurrent dropouts of strahl electrons, indicating disconnection from the Sun, provide further evidence for the HCS being the source of the beams. Around the HCS in E07, there were also proton beams but without electron strahl dropouts, indicating that their origin was not the local HCS reconnection exhaust.

Abstract Recent magnetospheric observations and three‐dimensional (3D) kinetic simulations have shown that plasma wave activities are significantly enhanced around the reconnection x‐line, implying that the reconnection process is fully 3D. However, how the turbulence affects the local reconnection process has been poorly understood so far. We find by means of large‐scale particle‐in‐cell simulation in 3D system that the local reconnection rate can be significantly enhanced, reaching 0.4, which is much larger than theoretical predictions for two‐dimensional (2D) reconnection. The large reconnection rate is associated with large energy conversion rate and strong electron acceleration. The enhancement of the reconnection rate is caused by local increases of electron momentum transport and pressure gradient force induced by turbulence, which can not occur in 2D system. The result is expected to give better interpretations to in‐situ satellite observations where magnetic reconnection proceeds in 3D system.

Abstract The generation of kinetic‐scale flux ropes (KSFRs) is closely related to magnetic reconnection. Both flux ropes and reconnection sites are detected in the magnetosheath and can impact the dynamics upstream of the magnetopause. In this study, using the Magnetospheric Multiscale satellite, 12,623 KSFRs with a scale

Electron‐only magnetic reconnection, a novel type of reconnection where only electron dynamics is involved, has recently been observed in turbulent plasmas in the Earth's magnetosphere. In this letter, using particle‐in‐cell simulations, we demonstrate that electron‐only reconnection can be created via laser‐plasma interactions. The reconnection current sheet is carried by electrons, and its width is at the electron inertial scale. Moreover, only electron outflow is observed, while the ion outflow is negligible. The duration of the reconnection is found to be within the electron scale, thus there is no sufficient time for ions to respond. The energy conversion during electron‐only reconnection mainly occurs in the vicinity of the X‐line, and is dominated along the perpendicular direction. By analyzing the Poynting flux patterns, we find that the reconnection electric field dominates the whole energy conversion. This study advances our knowledge of the energy dissipation mechanism in the electron‐only reconnection regime. Plain Language Summary: Magnetic reconnection is a fundamental energy converting process that occurs in space and laboratory plasma. Generally, magnetic reconnection involves both ion dynamics and electron dynamics. Recently, a new type of magnetic reconnection has been discovered in the Earth's turbulent magnetosheath and magnetotail, which is called electron‐only reconnection. In electron‐only reconnection, only electron outflow is observed since there is no time and/or space for ions to couple. In this study, by performing numerical simulations, we create the electron‐only reconnection via laser‐plasma interaction, and investigate the energy conversion during reconnection in detail. We find that both the spatial and temporal scale of the reconnection is within the electron scale. During magnetic reconnection, energy is transferred from the electromagnetic fields to the electrons, mainly occurring near the X‐line. The reconnection electric field plays a crucial role in energy conversion. This study improves our understanding of how energy is converted to electrons in electron‐only reconnection. Key Points: Simulations show that electron‐only magnetic reconnection can be created via laser‐plasma interactionsBoth the spatial and temporal scales of the reconnection are at the electron scale, and only electron outflow is observedEnergy conversion mainly occurs in the vicinity of the X‐line, and is driven by the reconnection electric field [ABSTRACT FROM AUTHOR]

Magnetic reconnection is a fundamental physical process of rapidly converting magnetic energy into particles. The electron diffusion region (EDR) is the crucial region during magnetic reconnection. The outer EDR, which also plays a crucial role in magnetic reconnection, is responsible for energy conversion. In the outer EDR, the electrons are decelerated and return the energy to the magnetic field on the pileup region behind the reconnection front. In the present study, we used the fully kinetic particle‐in‐cell simulation and revealed that part of decelerated electrons in the outer EDR could even move back to the inner EDR. This phenomenon is caused by the dominant contribution from the magnetic tension force, and it suggests a magnetic Marangoni effect in space plasma, similar to the Marangoni effect in fluids. Our results potentially propose a brand‐new physical process and a novel mechanism in the EDR during magnetic reconnection. Plain Language Summary: Plasma's energy can be changed through various approaches in the universe, and magnetic reconnection is one of those approaches to convert energy from the magnetic field to the plasma. In the reconnection site, the inner electron diffusion region (EDR) is an essential area where the energy is released, and the electron's energy is enhanced significantly. Meanwhile, in the outer EDR, the electrons are decelerated by the electric field, thus their energy decreases. However, part of those electrons can move backward to the inner EDR, and how this phenomenon comes up has no further investigation. In this study, we use numerical simulations to reveal the possible mechanism of this kind of electron's motion. It is found that the electron deceleration is caused by the magnetic tensor force. The electrons with specific conditions have the possibility to move backward. Those backflow electrons have a second chance to be accelerated again in the inner EDR. Such electron motion in plasma physics is not a kind of gyro movement but might indicate a so‐called magnetic Marangoni effect similar to the Marangoni effect in fluid physics. Our findings propose a novel mechanism associated with electron acceleration in the EDR during magnetic reconnection. Key Points: The magnetic tension force causes the deceleration of the electrons in the outer electron diffusion region (EDR) during magnetic reconnectionPartial electrons are decelerated and even move back to the inner EDR, and they are accelerated again and attain higher energyThe electron backflow motion in the outer EDR indicates a magnetic Marangoni effect in space plasma [ABSTRACT FROM AUTHOR]

We present Magnetospheric Multiscale (MMS) observations of a K‐H wave event under southward IMF conditions, accompanied by ongoing magnetic reconnection. The nonlinear K‐H waves are characterized by quasi‐periodic fluctuations, the presence of low‐density and high‐speed ions, and variations in the boundary normal vectors at both the leading and trailing edges. Our observations reveal clear evidence of on‐going magnetic reconnection through the identification of Alfvénic ion jets and the escape of energetic magnetospheric electrons. Among the 36 magnetopause current‐sheet crossings in this event, 19 exhibit unambiguous signatures of reconnection at both the leading (7) and trailing (12) edges. Notably, the estimated current‐sheet thicknesses at both edges are comparable to the ion‐inertial scale, confirming the compression effect resulting from the large‐scale evolution of the K‐H waves. The reconnection jets potentially contribute to the suppression of K‐H growth through boundary‐layer broadening and the development of complex flow and magnetic field patterns. Plain Language Summary: Kelvin‐Helmholtz (K‐H) waves and magnetic reconnection are two common occurrences at the Earth's magnetopause, playing crucial roles in the transfer of mass, momentum, and energy from the solar wind to the magnetosphere. While extensive research has been conducted on the relationship between K‐H waves and magnetic reconnection under northward interplanetary magnetic field (IMF) conditions, there is a notable gap in our understanding regarding the southward IMF scenario. This study presents the first observed event of K‐H waves under southward IMF conditions, accompanied by magnetic reconnection, and provides a detailed analysis of the characteristics of both phenomena. Through our observations, we investigate the correlation between K‐H waves and magnetic reconnection during southward IMF periods. Our findings suggest that the coexistence of K‐H waves and magnetic reconnection may be attributed to the promoting effect of K‐H waves on the occurrence of magnetic reconnection. Furthermore, it is likely that magnetic reconnection suppresses the evolution of K‐H waves, which could potentially contribute to the low likelihood of observing K‐H waves under southward IMF conditions. Key Points: The first report of K‐H waves and magnetic reconnection occurring simultaneously at the magnetopause LLBL under southward IMF conditionsThe reconnection ion jets are observed at both the leading and trailing edges of the K‐H wavesFavorable conditions for reconnection are produced by K‐H waves and reconnection may in turn affect the global evolution of the K‐H waves [ABSTRACT FROM AUTHOR]

Magnetospheric substorms are preceded by a slow growth phase of magnetic flux loading and current sheet thinning in the tail. Extensive data sets have provided evidence of the triggering of instabilities at substorm onset, including magnetic reconnection and ballooning instabilities. Using an exact kinetic magnetotail equilibrium we present particle‐in‐cell simulations which capture the explosive nature of substorms through a disruption of the dipolarization front by the ballooning instability. We use self‐consistent particle tracking to determine the nonthermal particle acceleration mechanisms. Plain Language Summary: Magnetospheric substorms are events featuring bursty flows of magnetized plasma, highly energetic particles, and intense polar auroras. Substorms play a key role in the response of the magnetosphere to variations in the incoming solar wind. The Earth's magnetic field lines are like elastic strings, and when they snap charged particles can be accelerated to high energies. Additionally, when there is enough plasma pressure pushing against the magnetic field, the magnetic field lines can develop an unstable oscillation known as a "ballooning instability" which is driven by the alignment of the plasma pressure gradient with magnetic field curvature. Using computer simulations that follow the trajectories of billions of particles in the Earth's magnetosphere and compute their self‐consistent electromagnetic forces, we show the importance of the interplay between reconnection and ballooning in the onset of substorms and acceleration of charged particles to high energies. These results have strong implications for the development of accurate models to predict space weather events and mitigate their damaging effects on critical infrastructure. Key Points: For the first time, an exact kinetic magnetotail equilibrium is used to model magnetospheric substorm onsetComparing 2D and 3D simulations reveals the importance of the coupling between magnetic reconnection and the kinetic ballooning instabilitySelf‐consistent particle trajectories are analyzed for the first time in a realistic fully kinetic magnetotail configuration [ABSTRACT FROM AUTHOR]

We present Magnetospheric Multiscale observations of an electron‐scale reconnecting current sheet in the mixing region along the trailing edge of a Kelvin‐Helmholtz vortex during southward interplanetary magnetic field conditions. Within this region, we observe intense electrostatic wave activity, consistent with lower‐hybrid waves. These waves lead to the transport of high‐density magnetosheath plasma across the boundary layer into the magnetosphere and generate a mixing region with highly compressed magnetic field lines, leading to the formation of a thin current sheet associated with electron‐scale reconnection signatures. Consistencies between these reconnection signatures and a realistic, local, fully‐kinetic simulation modeling this current sheet indicate a temporal evolution of the observed electron‐scale reconnection current sheet. The multi‐scale and inter‐process character of this event can help us understand plasma mixing connected to the Kelvin‐Helmholtz instability and the temporal evolution of electron‐scale reconnection. Plain Language Summary: Like wind blowing over water, the stream of ionized gas released from the Sun, called the solar wind, can lead to waves and rolled‐up vortex structures at the boundary of Earth's magnetosphere, called the magnetopause. These so‐called Kelvin‐Helmholtz waves have been shown to be connected to various different plasma processes on different scales. This multi‐scale and multi‐process character makes them an ideal candidate to study the relation between these processes from both spacecraft observations and simulations. By using spacecraft data from the Magnetospheric Multiscale mission, which was designed for the study of small‐scale plasma processes in Earth's magnetosphere, we show observations of electron‐scale magnetic reconnection, an explosive energy conversion process in plasmas, in a region along the trailing edge of these waves. These observations shed new light on the multi‐scale and multi‐process character of the Kelvin‐Helmholtz instability and the energy conversion processes along its boundary. Key Points: A reconnecting electron‐scale current sheet is observed by Magnetospheric Multiscale (MMS) in mixing plasma along the trailing edge of a Kelvin‐Helmholtz vortexRealistic 2.5D fully‐kinetic simulation shows reasonable agreement with MMS dataConsistencies between the simulation and MMS indicate a temporal evolution of the reconnecting current sheet [ABSTRACT FROM AUTHOR]

Magnetic flux ropes (MFRs) are significant regions for the production of energetic electrons in space and astrophysical plasmas. However, the research on electron heating and acceleration driven by turbulence in MFRs is still quite rare. Utilizing in‐situ measurements from MMS satellite, we study electron heating and associated electrostatic waves in an ion‐scale MFR within terrestrial super‐Alfvén plasma flow. Lower‐hybrid drift waves, generated locally in this MFR, can contribute to the perpendicular heating through their electrostatic potential accelerating electrons. The parallel heating is attributed to antiparallel propagating electron beams. These beams excite the broadband electrostatic waves that can interact with electrons and thermalize electrons. Our study promotes understanding of electron energization driven by plasma waves and wave‐particle interaction in MFRs. Plain Language Summary: Magnetic flux ropes (MFRs) are ubiquitous magnetic structures existing in space and astrophysical plasmas. They are produced by magnetic reconnection, and can in turn trigger small‐scale reconnection and modulate reconnection process. In addition, they are widely used to explain electron heating and acceleration, which is a long‐standing problem in space and astrophysical plasmas. Thus, they receive significant attention nowadays. However, there has been still lack of research on electron heating and acceleration driven by turbulence in MFRs. In our study, we find perpendicular electron heating is partly attributed to lower‐hybrid drift waves and parallel electron heating is closely related to antiparallel propagating electron beams, which excites strong broadband electrostatic waves that can result in thermalization of electrons. Key Points: Electron heating is detected inside an ion‐scale magnetic flux ropeLower‐hybrid drift waves can contribute to the perpendicular heating through their electrostatic potential accelerating electronsThe parallel heating is caused by electron beams, which excite the broadband electrostatic waves that can thermalize electrons [ABSTRACT FROM AUTHOR]

We investigate electrostatic waves in a magnetopause reconnection event around a secondary electron diffusion region. Near the current sheet mid‐plane, parallel electron beam‐mode waves are modulated by whistler waves. We conclude that the anisotropy of energized electrons in the reconnection exhaust excites whistler waves, which produce spatially modulated electron beams through nonlinear Landau resonance, and these beams excite beam‐mode electrostatic waves. In the separatrix region, parallel propagating electrostatic waves associated with field‐aligned electron beams and perpendicular propagating electron cyclotron harmonic waves with loss cone distributions exhibit modulation frequencies in the lower‐hybrid wave (LHW) frequency range. We infer that LHWs scatter electrons to produce beams and alter loss cones to modulate electrostatic waves. The results advance our understanding about the regimes and mechanisms of electrostatic waves in reconnection, with an emphasis on their coupling with lower‐frequency electromagnetic waves. Plain Language Summary: Magnetic reconnection is an important energy dissipation process at the Earth's dayside magnetopause. In its central region, plasmas deviate from the thermal equilibrium and form structured distribution functions, which excite plasma waves. We investigate high‐frequency electrostatic waves in an event, where the waves are associated with electron beam—plasma interaction or anisotropy of distribution functions. We find that electrostatic waves are driven and modulated by lower‐frequency waves, as the latter alters the particle distribution functions. The results help us understand how various processes couple with each other to achieve the energy dissipation. Key Points: Parallel electron beam‐mode waves are modulated by whistler near the current sheet mid‐plane, by driving beams through Landau resonanceElectron beam‐mode and cyclotron waves are modulated by lower‐hybrid waves near separatrices, with beam and loss cone distributions [ABSTRACT FROM AUTHOR]

The current sheet is crucial in releasing magnetic free energy in cosmic plasmas via fast magnetic reconnection or wave excitation. This research investigates the characteristics of the Martian tail current sheet by analyzing data acquired from the Mars Atmosphere and Volatile EvolutioN spacecraft over 7 years. For the first time, we find that approximately 15% of the current sheet events display reconnection signatures, including Hall magnetic fields and fast proton flows. These reconnecting current sheets are detected more frequently on Mars than on Earth. The Martian tail current sheet is first demonstrated to be on the proton scale, which can explain the high reconnection occurrence rate. The research also reveals that the current sheets are thinner in regions closer to Mars and in the –E hemisphere. On average, reconnecting current sheets carry high fluxes of protons rather than oxygen ions. Plain Language Summary: As a ubiquitous plasma configuration in various cosmic plasma environments, the current sheet is critical in facilitating the release of magnetic energy through explosive processes, such as fast magnetic reconnection. On Earth, magnetic reconnection in the tail current sheet can be responsible for triggering substorms and generating auroras. Recent observations have indicated that reconnection in the Martian tail enhances ion escape from the planet's atmosphere. However, the frequency of reconnection events in the Martian tail and their involvement in ion loss is still not fully understood based on previous few research. In this study, we use data from the Mars Atmosphere and Volatile EvolutioN spacecraft to study the Martian tail current sheet. For the first time, we find that almost 15% of the current sheet events on Mars have reconnection signatures, happening more often than on Earth. The high occurrence rate of magnetic reconnection at the Martian tail current sheet can be attributed to its extremely thin structure, which is on the scale of protons. Magnetic reconnection may drive high fluxes of hydrogen ions and thus potentially impact the evolution of the Martian atmosphere. Key Points: MAVEN recorded 880 current sheet events in the Martian tail in the past 7 years and about 15% of them show reconnection featuresThe average thickness of the current sheet is on the proton scale and is thinner in the −E hemisphereThe reconnecting tail current sheet carries a higher net tailward flux of hydrogen ions [ABSTRACT FROM AUTHOR]

With high‐resolution data from Magnetospheric Multiscale (MMS) mission, an ion‐scale flux rope (FR) with a heavily tilted axis is observed in the tailward outflow of a magnetic reconnection in the terrestrial magnetotail. Combined with the field‐aligned electron distribution and positions of MMS when the X‐line and FR are observed, the tilted axis is inferred to be caused by the extension of the X‐line in the dawn‐dusk direction. J · E′ is negative and electrons are losing energy in the FR. An ion‐scale electron vortex embedded in the plane perpendicular to the axis is observed inside FR. The induced magnetic field generated by the electron vortex has the same direction as the axial component, which can contribute to the axial component and increase the magnetic flux of the FR. Such electron vortex FRs may be an essential carrier of magnetic flux from near‐Earth X‐line to distant X‐line or interplanetary space. Plain Language Summary: Magnetic reconnection is an efficient energy and magnetic flux release process in the magnetotail. It is well known that dipolarization front is an important carrier of magnetic flux to Earth. However, how the magnetic flux transports at the tailward side is rarely concerned. In this work, we present an observation of an electron vortex flux rope as a new possible candidate. The embedded electron vortex generates an induced magnetic field with the same direction as the axial component of the flux rope, which is self‐consistent and can contribute to the enhancement of the magnetic flux carried by the flux rope by converting energy from electrons to the magnetic field. Our observations can contribute to understand the dynamics of the magnetotail. Key Points: An ion‐scale flux rope with an electron vortex embedded is observed in the tailward outflow of a magnetic reconnection eventThe tilted axis of the flux rope is due to the extension of the X‐line in the dawn‐dusk directionThe electron vortex flux rope may be an essential carrier of magnetic flux to distant tail or interplanetary space [ABSTRACT FROM AUTHOR]

Abstract Magnetic reconnection is a fundamental physical process of rapidly converting magnetic energy into particles. The electron diffusion region (EDR) is the crucial region during magnetic reconnection. The outer EDR, which also plays a crucial role in magnetic reconnection, is responsible for energy conversion. In the outer EDR, the electrons are decelerated and return the energy to the magnetic field on the pileup region behind the reconnection front. In the present study, we used the fully kinetic particle‐in‐cell simulation and revealed that part of decelerated electrons in the outer EDR could even move back to the inner EDR. This phenomenon is caused by the dominant contribution from the magnetic tension force, and it suggests a magnetic Marangoni effect in space plasma, similar to the Marangoni effect in fluids. Our results potentially propose a brand‐new physical process and a novel mechanism in the EDR during magnetic reconnection.

Abstract With high‐resolution data from Magnetospheric Multiscale (MMS) mission, an ion‐scale flux rope (FR) with a heavily tilted axis is observed in the tailward outflow of a magnetic reconnection in the terrestrial magnetotail. Combined with the field‐aligned electron distribution and positions of MMS when the X‐line and FR are observed, the tilted axis is inferred to be caused by the extension of the X‐line in the dawn‐dusk direction. J · E′ is negative and electrons are losing energy in the FR. An ion‐scale electron vortex embedded in the plane perpendicular to the axis is observed inside FR. The induced magnetic field generated by the electron vortex has the same direction as the axial component, which can contribute to the axial component and increase the magnetic flux of the FR. Such electron vortex FRs may be an essential carrier of magnetic flux from near‐Earth X‐line to distant X‐line or interplanetary space.

Abstract We investigate electrostatic waves in a magnetopause reconnection event around a secondary electron diffusion region. Near the current sheet mid‐plane, parallel electron beam‐mode waves are modulated by whistler waves. We conclude that the anisotropy of energized electrons in the reconnection exhaust excites whistler waves, which produce spatially modulated electron beams through nonlinear Landau resonance, and these beams excite beam‐mode electrostatic waves. In the separatrix region, parallel propagating electrostatic waves associated with field‐aligned electron beams and perpendicular propagating electron cyclotron harmonic waves with loss cone distributions exhibit modulation frequencies in the lower‐hybrid wave (LHW) frequency range. We infer that LHWs scatter electrons to produce beams and alter loss cones to modulate electrostatic waves. The results advance our understanding about the regimes and mechanisms of electrostatic waves in reconnection, with an emphasis on their coupling with lower‐frequency electromagnetic waves.

Abstract The current sheet is crucial in releasing magnetic free energy in cosmic plasmas via fast magnetic reconnection or wave excitation. This research investigates the characteristics of the Martian tail current sheet by analyzing data acquired from the Mars Atmosphere and Volatile EvolutioN spacecraft over 7 years. For the first time, we find that approximately 15% of the current sheet events display reconnection signatures, including Hall magnetic fields and fast proton flows. These reconnecting current sheets are detected more frequently on Mars than on Earth. The Martian tail current sheet is first demonstrated to be on the proton scale, which can explain the high reconnection occurrence rate. The research also reveals that the current sheets are thinner in regions closer to Mars and in the –E hemisphere. On average, reconnecting current sheets carry high fluxes of protons rather than oxygen ions.

The near lunar surface contains small‐scale magnetic field structures that provide a natural test bed for observing plasmas with a non‐zero Hall electric field, as well as potentially facilitating electron‐only reconnection. This study presents observational evidence of magnetized electrons as well as demagnetized ions when THEMIS‐ARTEMIS probe B reached an altitude of ∼15 km above the lunar surface. Additionally, observations suggest the presence of a field line topology change and traversal of a closed magnetic field structure containing solar wind electrons, suggestive of magnetic reconnection having occurred at some point between the solar wind interplanetary magnetic field and a lunar crustal magnetic field. Thus, the observations presented here are consistent with previous studies that predict prominent Hall electric fields near lunar crustal magnetic fields and further suggest that the solar wind interplanetary magnetic field may reconnect with lunar crustal magnetic fields, most likely via electron‐only reconnection. Plain Language Summary: While interactions between the solar wind and the Earth's magnetosphere have been well studied, there is still much to be learned by studying the interactions between the solar wind and the small‐scale lunar magnetic fields. Due to the small‐scale nature of the lunar magnetic fields, previous studies have suggested that the ions do not respond in the same manner as the electrons. The resulting effects lead to an electric field near regions of lunar magnetic fields. This study presents observational evidence of the aforementioned phenomena. Additionally, the spacecraft observations also suggest that magnetic reconnection, or the breaking of the lunar magnetic field lines and reconnection to the magnetic field in the solar wind, was occurring between the solar wind and the lunar magnetic fields. Key Points: Observations suggest magnetic reconnection occurs between the solar wind IMF and lunar crustal magnetic fieldsElectron pitch angle and velocity distributions suggest the spacecraft traversed a closed magnetic topology containing solar wind electronsWe report in‐situ observations of demagnetized ions and associated Hall electric fields near the lunar surface [ABSTRACT FROM AUTHOR]