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Electron pitch angle distributions (PADs) are crucial to revealing electron acceleration and heating in geospace. The electron PADs in the Earth's magnetotail have been widely studied by statistical or case analysis. However, the statistical features of electron PADs in tailward flows are still unclear. We survey data from the Magnetospheric Multiscale (MMS) satellite to statistically investigate electron PADs in tailward flows in the Earth's magnetotail for the first time. We find that for most (66.3%) tailward flows, electrons with energy from 0.1 to 30 keV are mainly field‐aligned. The PADs of suprathermal (>2 keV) electrons in a part of tailward flows (26.3%) are mostly isotropic. Additionally, the perpendicular‐dominated PADs of suprathermal electrons only exist in a few (7.4%) tailward flows. According to the different dominant PADs of suprathermal electrons, the tailward flows are classified into three types: field‐aligned‐dominated type, isotropic‐dominated type and perpendicular‐dominated type flows. The dependence of electron PADs on plasma environmental parameters is investigated in these three types of flows. For field‐aligned‐dominated type flows, the field‐aligned anisotropy decreases toward the central plasma sheet (CPS) and with the increase of the energy. In addition, it is found that the field‐aligned anisotropy in the field‐aligned‐dominated tailward flows reduces noticeably when the |Vix| exceeds 800 km/s. In isotropic‐dominated type flows, the field‐aligned anisotropy of electrons with energy ≥10 keV also shows a slight decreasing trend toward the CPS. For perpendicular‐dominated type flows, the perpendicular anisotropy exhibits two non‐monotonic processes, initially increasing and then decreasing with the increase of distance from the CPS; while becomes more evident for higher energy electrons. Our statistical results indicate that in tailward flows, electron anisotropy depends on the distance from the CPS, energy and plasma flow velocity. Tailward flows are associated with the transport of plasma toward the distant tail, and the statistical analysis of electron PADs in these flows can improve our understanding of the related electron dynamics in the magnetotail. Key Points: Statistically features of field‐aligned‐dominated, isotropic‐dominated and perpendicular‐dominated type tailward flows are revealedFor the field‐aligned‐dominated type flows, the field‐aligned anisotropy decreases toward the central plasma sheet and with the increase of the energyThe perpendicular pitch‐angle anisotropy in the perpendicular‐dominated type flows is more evident for higher energy electrons [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]

Identifying how different wave modes interaction with each other is an important topic in space physics. Using measurements from the Magnetospheric Multiscale (MMS) mission, we report an event in the Earth's magnetosheath where ultra‐low‐frequency (ULF) waves, whistler waves, and quasi‐electrostatic whistler harmonics were observed simultaneously. Specifically, our analyses show that the parallel components of ULF waves modulate the electron butterfly distributions which provide the free energy to the excitation of the observed whistler waves. Meanwhile, quasi‐electrostatic waves sharing frequencies that are nearly integral multiples of the frequency of the observed whistlers are identified as nonlinear harmonics of whistler waves. The close correlations between the whistler waves and the electric field harmonics, as well as the high bicoherence indexes within the frequency ranges of the whistlers and harmonics, suggest the significant nonlinear couplings between the whistler waves and quasi‐electrostatic whistler harmonics. Our work provides new insights to the interactions between waves at different frequency bands. Key Points: Ultra‐low‐frequency (ULF) waves, whistler waves, and quasi‐electrostatic whistler harmonics are observed simultaneously in the magnetosheath plasmaULF waves modulate the electron butterfly shaped distributions which provide free energy for the excitation of the observed whistler wavesQuasi‐electrostatic waves are identified as the whistler harmonics, and may be generated by the wave‐wave nonlinear coupling [ABSTRACT FROM AUTHOR]

Heavy particles are extensively detected in the space environment, especially in the solar wind and interplanetary magnetosphere. Various physical processes can be affected by the physical dynamics of heavy particles. One of the processes is magnetic reconnection, which converts the energy from the magnetic field to the particles. In the present study, we investigate the impact of heavy particles with increasing mass (i.e., mass-loading effect) on energy conversion rate during magnetic reconnection. The declined reconnection rate and energy conversion rates by this effect are captured as reported previously. After considering three major regions in reconnection, it reveals that the mass-loading effect decreases more energy conversion rate of positive species at the separatrix, affects the heavier species less in the inner electron diffusion region (EDR), and propels the formation of a non-zero electric field at reconnection front (RF). Our results provide a more comprehensive understanding of the magnetic reconnection with complicated plasma components. [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]