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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 DF The strong energy conversion at this DF is mainly caused by the magnetic reconnection The duskward diverted flow compresses the bent DF caused by interchange instability, leading to the reconnection

The Kolmogorov scaling in the inertial range of scales is a distinct characteristic of fully developed turbulence, and studying it offers valuable insights into the evolution of turbulence. In this work, we perform a statistical survey of the power spectra with the Kolmogorov scaling in Saturn's magnetosphere using Cassini measurements. Two cases study show that both magnetic‐field and electron density spectra exhibit f −5/3 at the MHD scales. The statistical analysis reveals a wide‐ranging and abundant presence of Kolmogorov spectra throughout magnetosphere, observed across all local times. Interestingly, the occurrence rate of these Kolmogorov‐like events within Saturn's magnetosphere surpasses that observed in the planetary magnetosheath. The measurements of magnetic compressibility for the Kolmogorov‐like events show the dominance of incompressible Alfvénic turbulence (44.64%) with respect to magnetosonic‐like one (6.94%). In addition, the source and evolution of the turbulent fluctuations are further discussed. Plain Language Summary Turbulence is ubiquitous in space and astrophysical plasmas, such as the solar wind, planetary magnetospheres, and the interstellar medium. Plasma turbulence has been widely studied in the solar wind and planetary magnetosheaths, but much less in the planetary magnetospheres. In the solar wind, power spectral density of the magnetic field fluctuations generally follows the so‐called Kolmogorov spectrum f −5/3 at the magnetohydrodynamic (MHD) scales, which suggests a fully developed turbulent state. In this study, we have discovered the widespread presence of Kolmogorov spectra in the Saturn's magnetosphere. The spatial distribution and nature of turbulent fluctuation for the Kolmogorov‐like events are also investigated in detail. Key Points Magnetic field and electron density spectra have Kolmogorov scaling of f −5/3 at MHD scales in Saturn's magnetosphere The spatial distribution of the Kolmogorov spectra within Saturn's magnetosphere reveals the extensive occurrence of Kolmogorov‐like events The fluctuations for Kolmogorov‐like events are dominated by Alfvénic modes (44.64%) with respect to magnetosonic‐like one (6.94%)

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 time Proton and oxygen ions from the mini‐magnetosphere are accelerated during magnetic reconnection Magnetic reconnection at the mini‐magnetopause could cause solar wind to enter the mini‐magnetosphere

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 simulations The formation of the crater structure appears to be associated with the high‐speed electron jets from inner electron diffusion region A possible scenario that electron outflow constantly strikes the RF and then causes the formation of the crater structure

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 reconnection Partial electrons are decelerated and even move back to the inner EDR, and they are accelerated again and attain higher energy The electron backflow motion in the outer EDR indicates a magnetic Marangoni effect in space plasma

Dipolarization fronts (DFs) host plentiful dynamics in the magnetotail. Small‐scale magnetic structures and waves are frequently found at and around the DFs. Whistler waves are closely related to DFs, and the flux pileup regions (FPRs) behind DFs are thought to be the source regions of the whistler waves around DFs. Statistically, whistler waves are much more frequently observed in FPRs than at DFs. Here, we present an observation of whistler waves in a magnetic hole at a DF. Theoretical calculations show that the observed whistler waves can be trapped in the magnetic hole. Furthermore, theoretical calculations suggest that whistler waves cannot be trapped at a DF if the DF has no sub‐structures. Our results indicate the importance of the magnetic structures on the propagation of whistler waves around the DFs and could explain why whistler waves are rarely observed at the DFs. Plain Language Summary Dipolarization fronts (DFs), as the boundary separating the hot and tenuous high‐speed plasma flow and the cold and dense background plasmas, are important in transporting energy and magnetic fluxes from magnetotail to the Earth. Abundant dynamic processes have been observed related to DFs. Occasionally, magnetic structures can be found at DFs, for example, magnetic holes, current sheets, etc. Various waves, especially whistler waves, have been observed around DFs. The flux pileup regions behind DFs have been thought to be the source regions of whistler waves around DFs. However, observations of whistler waves at DFs are much fewer in contrast to those in flux pileup regions. Using data from the Magnetospheric Multiscale (MMS) mission, we found whistler waves in a magnetic hole at a DF. By calculating the perpendicular refractive index, we find the whistler waves observed here are trapped in the magnetic hole. Besides, we consider a DF without a small‐scale magnetic structure, and the theory predicts that no whistler waves can be trapped at the DF. Our work implies the importance of the magnetic structures on the propagation of the whistler waves around DFs and provides a possible explanation for why so few whistler waves are observed at DFs. Key Points Whistler waves are observed in the magnetic hole at a dipolarization front Theory predicts the observed whistler waves can be trapped in the magnetic hole Theory predicts that whistler waves cannot be trapped at a dipolarization front without a small‐scale magnetic structure

Assisted by the Magnetospheric Multiscale mission capturing unprecedented high-resolution data in the terrestrial magnetotail, we apply a local streamline-topology classification methodology to investigate the categorization of the magnetic field topological structures at kinetic scales in the turbulent reconnection outflow. It is found that strong correlations exist between the straining and rotational part of the velocity gradient tensor as well as the magnetic field gradient tensor. Strong energy dissipation prefers to occur at regions with high magnetic stress or current density, which is contributed mainly by O-type topologies. These results indicate that the kinetic structures with O-type topology play a more important role in energy dissipation in turbulent reconnection outflow.

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) simulations A larger guide field can promote the generation of O‐type topology in the turbulent outflow of the reconnection Higher energy conversion is contributed by those O‐type topologies in the presence of a larger guide field

Magnetopause reconnection plays a significant role in transferring plasma and energy from the solar wind to planetary magnetospheres. Using a Cassini measurement, we reported a magnetopause reconnection at Saturn, identified by the Hall magnetic field and the mixture of magnetosheath electron population and magnetosphere electron population near the X-line. Then, the mirror mode (MM) structures are identified both in the magnetosheath and the magnetosphere. Further analysis suggests that the MM structures were generated in the magnetosheath and traveled across the magnetopause. We infer that MM structures enter the magnetosphere through the magnetopause reconnection. This result provides a possible source for the MM structures in the magnetosphere. These observations and analyses also help to further understand the influence of Saturn’s magnetopause reconnection on the magnetosphere dynamics.

Interplanetary coronal mass ejections (ICMEs) are different from the typical solar wind in their compressibility and levels of fluctuations in magnetic field, proton velocity, density, and temperature, making them a unique environment for studying turbulence properties. However, the difference between cascade rates in the ICMEs and typical solar wind, the comparison between cascade rates estimated by compressible and incompressible models, and how cascade rates in the ICMEs evolve with the radial distance from the Sun are still unclear. Using the data of 33 ICMEs observed between 0.305 au and 1.015 au by Parker Solar Probe and Solar Orbiter, we statistically investigated the incompressible and compressible inertial range turbulent cascade rates (ϵi and ϵc) in and around ICMEs. ϵi and ϵc in the sheaths and ejecta of ICMEs are always larger than in the upstream solar wind before them. ϵi and ϵc in the downstream solar wind behind ICMEs can be amplified after the ICMEs pass. ϵc is always larger than ϵi in all ICME subregions, indicating the amplifying effects of compressibility and levels of fluctuations in proton density, velocity, and temperature on the cascade rates of ICMEs. ϵi and ϵc in all ICME subregions decrease with the increase of the radial distance. These results shed light on our understanding of turbulent cascade rates and their radial evolution in ICMEs.