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PM10 and size-resolved particles (9-stage) were simultaneously collected at Mt. Hua and Mt. Tai in central and east China during the spring of 2009 including a massive dust storm occurring on 24 April (named as DS II), and determined for organic compounds to investigate the impact of dust storm on organic aerosols. High molecular weight (HMW) n-alkanes, fatty acids, and fatty alcohols and trehalose sharply increased and almost entirely stayed in coarse particles when dust storm was present, suggesting that high level of organic aerosols in the mountain atmospheres during the event largely originated from Gobi desert plants. However, most anthropogenic aerosols (e.g. PAHs, and aromatic and dicarboxylic acids) during the event significantly decreased due to a dilution effect, indicating that anthropogenic aerosols in the mountain atmospheres during the nonevent period largely originated from local/regional sources rather than from long-range transport. Trehalose, a metabolism product enriched in biota in dry conditions, was 62 ± 78 and 421 ± 181 ng m−3 at Mt. Hua and Mt. Tai during DS II, 10–30 times higher than that in the nonevent time, indicating that trehalose may be a tracer for dust emissions from Gobi desert regions. Molecular compositions of organic aerosols in the mountain samples demonstrate that domestic coal burning is still the major source of PAHs in China. n-Alkanes and fatty acids showed a bimodal size distribution during the nonevent with a major peak in fine mode (2.1 μm). The coarse mode significantly increased and even dominated over the whole size range when dust was present. Glucose and trehalose were also dominant in the coarse mode especially in the DS II time. PAHs and levoglucosan concentrated in fine particles with no significant changes in size distribution when dust storm occurred. However, phthalic and succinic acids showed bimodal size distribution pattern with an increase in coarse mode during the event, because both are formed via a gas phase oxidation and a subsequent condensation/adsorption onto aerosol phase. In contrast, terephthalic and malic acids are mostly emitted from combustion process as fine particles, thus both showed a fine mode pattern during the whole campaign with a minor peak in coarse mode caused by an increased coagulation with dust during the event. Geometric mean diameters (GMDs) of the organic aerosols above are in general larger at Mt.~Hua than at Mt. Tai during the nonevent period. We found that during the event GMD of the fine mode organics that derived mostly from the local/regional sources rather than Gobi desert became smaller while GMD of them in coarse mode became larger. Such a splitting in sizes during the event is most likely caused by decreased fine particle coagulation due to dilution and increased adsorption/coagulation with dust.

Abstract 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.

Abstract 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.

Abstract 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.

Abstract 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.

Abstract Electron vortices are usually embedded within different magnetic structures in space plasmas. The effects, including the nonideal electric field, energy dissipation and magnetic field, of electron vortices on these magnetic structures are still unclear. Utilizing the unprecedented high‐resolution data from the Magnetospheric Multiscale mission in the terrestrial magnetosheath, we statistically investigate these effects on magnetic structures. Both nonideal electric fields and energy dissipation have no obvious correlations with the scales of electron vortices. However, compared to the scales, stronger correlations are found between the vorticities of electron vortices and nonideal electric fields, and energy dissipation, respectively. Most of electron vortices have positive contributions to magnetic fields of magnetic structures, such as strengthening the decrease (or increase) of Bt for current sheets and magnetic holes (or flux ropes and magnetic peaks). Our results reveal that the electron vortices play an important role in the evolution of magnetic structures.

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.

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 In Saturn's magnetosphere, the plasma temperature increases with radial distance, requiring a heating mechanism to counteract the adiabatic cooling effect of expanding plasma. To explore potential heating source, we perform a statistical study about intermittent structures and intermittent heating in Saturn's magnetosphere based on the observations from the Cassini spacecraft. Partial Variance of Increments (PVI) technique is used to measure the intermittency of magnetic field and identify the intermittent structures. It is found that the electron temperature has a rising trend as the increase of magnetic field intermittency, implying the occurrence of electron heating in the intermittent structures. Additionally, the turbulence heating rate also exhibits an increasing trend as the increase of probability density of intermittent structures. Our results evidence the effect of intermittent heating in the Saturn's magnetosphere, and suggest that intermittent structures with high magnetic field intermittency play an important role in turbulence heating.

Solar activities have an extraordinary impact on interplanetary space, enriching the plasma dynamics including turbulent heating of various species. The small fraction of alpha particles is believed to play a significant role in the turbulent dynamics of the solar wind. Here we present fully kinetic particle-in-cell simulations to reveal the influences of the alpha particles in decaying plasma turbulence. Multiple run cases with different controlled variations of proton and alpha density are performed to compare and evaluate the energy conversion processes. It is found that the alpha particles can suppress the energy conversion rate with increasing density. Besides, the alpha particles show more heating intermittency than the proton species. Interestingly, on the other hand, the electrons do not show any change in their dynamics, including overall heating. These two positive charge species have more correlation in temperature anisotropy as their densities are comparable. Our results provide valuable insights on the turbulence with different species compositions to a certain extent, especially with abundant heavy particles.

Based on high-resolution measurements from the Magnetospheric Multiscale mission from 2015 May to 2018 June, we statistically investigate the properties of small-scale field-aligned currents (SFACs) in the magnetopause boundary layer. A total of 2235 SFACs are successfully identified. The durations of SFACs mainly fall between 0.2 and 0.3 s. Over 90% of SFACs have a width of less than 1 ion inertia length and are primarily distributed from 5 to 25 electron inertia lengths, implying that the SFACs belong to the kinetic-scale current layer. The main carriers of SFACs are electrons, and over 70% of SFACs exhibit net energy dissipation (i.e., J · E ′ > 0) with the majority of energy dissipation taking place in the parallel direction. SFACs are widely distributed spatially, and the occurrence rate of SFACs is higher in the boundary layer closer to the magnetosphere. Additionally, less than half of the total SFACs are identified in well-known structures, including the magnetic reconnection region, flux transfer event, Kelvin–Helmholtz vortex, and exhaust region, and 54% of the SFACs are in the “others” unknown structures. These results improve our comprehension of the current system at the magnetopause and the roles of SFACs in the coupling between the solar wind and magnetosphere.

Space plasmas are turbulent and maintain different types of critical points or flow nulls. Electron vortex, as one type of flow null structure, is crucial in the energy cascade in turbulent plasmas. However, due to the limited time resolution of the spacecraft observations, one can never analyze the three-dimensional properties of the electron vortex. In the present study, with the advancement of the FOTE-V method and the unprecedented high-resolution measurements from four Magnetospheric Multiscale spacecraft, we successfully identify the electron vortex and then reconstruct its three-dimensional topology of the surrounding electron flow field. The results of the reconstruction show that the configuration of the electron vortex is elliptical. Comparison between the observation and reconstruction scales of the vortex indicates the reliable reconstruction of the flow velocity. Our study sheds light on the understanding of the topology and property of the electron vortex and its relationship with kinetic-scale magnetic holes.

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.