Like Earth’s space, the Martian space constitutes a collisionless plasma environment. Consequently, the cross-scale energy transfer inherent to the multi-scale nature of collisionless plasmas—a process widespread in Earth’s space—is theoretically expected in Martian space. However, direct evidence for cross-scale energy transfer driven by cross-scale wave-particle interaction—the new model established in Earth’s space—remains elusive in Martian space. Utilizing data from the Mars Atmosphere and Volatile Evolution (MAVEN) and Tianwen-1 spacecrafts, we present the definitive observational evidence for the existence of such process in Martian foreshock region. Fast magnetosonic waves drive enhancements of electron perpendicular energy at their crests through Betatron acceleration, producing a perpendicular temperature anisotropy of the 20–200 eV population to supply the free energy for the excitations of whistler-mode waves. This process constitutes a direct manifestation of energy cascade from ion down to electron scales. Our study discovers a shared process in the terrestrial and Martian space, a finding that can carry broad implications for understanding space environments across planetary systems.

Abstract The polarity inversion line (PIL) in active regions (ARs) is considered to be closely associated with solar flare eruptions. In this study, we rigorously constructed standardized data sets based on time series of different lengths using Space‐weather HMI Active Region Patches (SHARP) parameters calculated along the PIL. We compared the performance of traditional non‐sequential models and a time‐series model in solar flare prediction tasks, as well as the predictive performance of time‐series models with different input lengths within the CNN–BiLSTM–AT framework. The main findings of this study are summarized as follows: (a) SHARP parameters computed along the PIL consistently yield better prediction performance than those calculated over entire active regions. (b) In realistic and highly imbalanced prediction scenarios, the time‐series model outperforms non‐sequential models, achieving an F1 score of 0.59 for strong‐flare prediction. (c) Robustness tests and sliding‐window probability forecasts further demonstrate the practical feasibility of the proposed approach. These results provide useful guidance for data representation and model selection in solar flare forecasting.

A fundamental yet still poorly understood question in solar wind–magnetosphere interaction is how energy from solar wind is transferred into Earth's magnetosphere and subsequently transferred across scales. Utilizing high-resolution joint measurements from NASA’s MMS and THEMIS missions, we reveal a new pathway for solar wind energy from its global-scale injection into Earth’s magnetosphere to its cross-scale cascade down to electron scales, predominantly mediated by cross-scale wave-particle and wave-wave interactions. Enhancements in solar wind dynamic pressure directly drive solar wind energy into Earth’s magnetosphere in the form of ultra-low frequency (ULF) waves and mirror-mode structures. Their coupling adiabatically modulates electron distributions, producing butterfly distributions to supply sufficient free energy for generating whistler-mode waves within ULF wave troughs. Concomitantly, the whistler-mode harmonics emerge from nonlinear wave couplings. Throughout, energy is also transferred from ions to electrons via mirror-mode structures. These findings advance our understanding of energy transfer chain during the interactions between solar wind and Earth’s magnetosphere.

Foreshock Bubbles (FBs) are transient structures in the Earth’s foreshock region, which are diamagnetic cavities formed by hot ion concentration around interplanetary magnetic field discontinuities and have significant compressional boundary shocks contributed to particle acceleration. We present here Cluster observations of FB events from January 2002 to April 2007 that each was encountered by all four spacecraft in order to accurately determine the parameters of its boundary shock. Statistical distributions show that the majority of the FB boundary shocks are supercritical and steep with large magnetic compression ratios and are in quasi-perpendicular direction to their upstream magnetic field. The magnetic compression ratios of FB boundary shocks are positively correlated with their shock normal angles. Additionally, the magnetic compression ratios increase with increasing upstream incident velocities, which is interpreted as a manifestation of diamagnetic Hall current generation inside the boundary. These results along with the conclusions given in previous numerical simulations and laboratorial experiments suggest a fast formation of a sharp boundary shock by the Larmor coupling between the super-thermal ions and magnetized ambient plasma in a hot plasma expanding process.

Utilizing joint observations from the Magnetospheric Multiscale (MMS) and OMNI spanning from 2017 to 2021, we investigate the response of the Earth's plasma sheet (PS) to solar wind (SW) forcing. The PS is divided into three key regions in the downtail (X < -10 R-E, Geocentric Solar Magnetospheric), that is, the current sheet (CS), central plasma sheet (CPS), and plasma sheet boundary layer, using a hybrid filter-decision tree model (HFDTM). The PSs of different regions were analyzed under four upstream SW speed and interplanetary magnetic field (IMF) conditions: low-speed northward (LSNW), low-speed southward (LSSW), high-speed northward (HSNW), and high-speed southward (HSSW). For each regime, we perform a comprehensive statistical analysis of key physical parameters, including the convective electric field (E-CY), kinetic electric field (E-K), and ion density (n(i)) and temperature (T-i). Our main finding are as follows: (a) Ec(Y) in the plasma sheet shows a monotonic increase with rising SW-E-CY0 across all 3 PS regions under southward IMF, but ambiguous correlation with SW under northward IMF; (b) n(i) shows a strong correlation with the solar wind under both IMF orientations, particularly during low-speed conditions; and (c) E-K and T-i consistently display weak correlations across all regimes, highlighting the dominant role of internal processes in plasma sheet evolution. These results support a dual-path coupling mechanism between the solar wind and the magnetosphere, characterized by persistent mass loading across all regimes, and an energy transfer pathway that is strong under the southward IMF but weak and primarily governed by internal energy relaxation processes under northward IMF.

This study investigates potential anomalous electromagnetic signals and their characteristics during the 2022 Mexico M7.6 earthquake by integrating the satellite data with a lithosphere-atmosphere-ionosphere (LAI) coupling propagation model for extremely low frequency (ELF) electromagnetic waves. Satellite observations and wave vector analysis demonstrate that a significant upward-propagating ELF electromagnetic radiation anomaly emerged south of the epicentral region eight days before the earthquake, with signals concentrated in the 200−500 Hz frequency range. The full-wave simulations were employed to further analyze the spatial distribution characteristics of the anomaly and its frequency dependence. The simulation results reveal that the radiation entering the ionosphere exhibits a beam-like structure displaced southward with the wave energy reaching satellite altitude decreasing as frequency increases, while a distinct narrow-band (400−500 Hz) absorption feature observed. The qualitative agreement in spatial displacement and spectral characteristics between simulations and observations provides supporting evidence for the interpretation that the observed anomaly originated from a subsurface source, and contributes to our understanding of cross-sphere propagation mechanisms of seismo-electromagnetic radiation.

Solar wind alpha particles exhibit preferential heating and acceleration relative to protons; however, their behavior in the vicinity of turbulent coherent structures remains less understood. We report the first evidence of localized alpha particle and proton heating within coherent structures identified using the Partial Variance of Increments (PVI) method, based on Parker Solar Probe (PSP) observations. Our results show that high-PVI events are associated with significant, species-dependent temperature enhancements: protons undergo a relative larger temperature increase than alpha particles. This preferential proton heating produces a localized decrease in the alpha-to-proton temperature ratio, indicating that the plasma is driven toward thermal equilibration between species. The heating is also anisotropic, being dominated by enhancements in the perpendicular temperature. These temperature-signatures coincide with a pronounced reduction in the normalized alpha-proton differential flow speed and a localized minimum in the Coulomb collision age, suggesting that the relaxation is affected primarily by collisionless kinetic effects. These findings provide new insight into the intermittent energy conversion and ion thermodynamics in the solar wind.

The Earth's magnetospheric cusp serves as a key channel for solar wind particles to enter the magnetosphere and for ionospheric ions to escape. The plasma density is central to understanding of these processes. Based on Cluster observation (collected between 2001 and 2010) of 878 cusp-crossing events, we performed a statistical study on the three-dimensional distribution of cusp ion density, as well as the primary influencing factors.Our findings show that the highest density occurs around MLT=12 in both hemispheres, declining as MLT shifts away from noon. In SM coordinates, the maximum density appears near the equatorward boundary along the X direction, while variations in the Z direction are relatively small. This feature can be explained by the inhomogeneity of magnetic pressure. We also observed that solar wind ions, as the main source, most effectively enter the cusp around noon and diffuse toward dawn and dusk. As the AE index grows, the polar ionosphere becomes increasingly important, supplying particles from a wide range of MLT values to the cusp. Finally, the cusp density is found to be correlated with dipole angle, suggesting the cusp’s ability to funnel charged particles depends on how Earth’s magnetic field is oriented.

Properties of the solar wind in different types of plasma (e.g., heliospheric current sheet, coronal hole, ejecta, sub-Alfvénic) are known to exhibit distinct features. Based on Parker Solar Probe measurements of the solar wind in the inner heliosphere, we compare the similarities and differences between two streams originating from different sources at the same radial distance. Despite sharing similar properties, including cross helicity, residual energy, Elsasser ratio, and magnetic compressibility, notable differences are observed. For the solar wind associated with active regions, the turbulence exhibits lower magnetic field fluctuation amplitudes, shallower magnetic field spectrum, and stronger intermittency, whereas the turbulence associated with coronal holes displays opposite characteristics. The switchback properties of these two streams are also discussed. Our results further explore the variabilities of solar wind turbulence, which may have implications for solar wind heating and acceleration.

The accurate classification of plasma regions is a critical challenge in space science, with identifying dynamic boundary layers (BLs) being particularly complex. This study introduces a novel wavelet-decision tree classifier (WDTC) designed to automate BL detection. Unlike conventional machine learning methods that rely on raw satellite measurements, the WDTC utilizes processed parameters derived from wavelet analysis as inputs to the decision tree algorithm. For each in situ measurement, including magnetic field strength (B), plasma density (n), velocity (V), and temperature (T), the wavelet analysis generates two features: wavelet energy and wavelet entropy. This results in a total of eight input parameters (two for each of the four in situ measurements) for the decision tree. By incorporating these distinctive wavelet-derived features, the WDTC enhances its ability to accurately and efficiently identify BLs within complex plasma environments. The model was applied to data from the Magnetospheric Multiscale (MMS) mission, focusing on the dayside region, and successfully differentiated between the solar wind, bow shock, magnetosheath, magnetopause, and magnetosphere. From September 15 to December 31, 2015, the WDTC identified 711 BL crossings, including 295 bow shock events and 416 magnetopause crossings. Beyond its scientific applications, the WDTC provides high-quality training datasets and a reliable data labeling tool, contributing to neural network training efforts.

The Earth's magnetospheric cusp region is an important pathway for solar wind particles entering the magnetosphere and ionospheric ions escaping. The plasma density is a key parameter for understanding this physical process. Based on measurements from the Cluster‐3 spacecraft (2001–2010), we selected 878 cusp crossing events (470 in the northern and 408 in the southern hemisphere) and statistically studied the three‐dimensional distribution of cusp ion density, its causes, and influencing factors. Our analysis revealed that cusp density is highest at MLT = 12 and decreases as MLT moves away from 12 in both hemispheres; in Solar Magnetic coordinates, the maximum density occurs near the equatorward boundary in the X direction, while in the Z direction, the density shows slight changes. This feature may be largely influenced by the inhomogeneity of magnetic pressure. Furthermore, we found that as the dominant source, solar wind ions enter the cusp effectively near noon and diffuses toward dawn and dusk; the polar ionosphere source becomes important with increasing AE index, transporting particles from a wide MLT range to the cusp; and the dipole tilt angle significantly affects cusp density.

We present consecutive observations of Flux Transfer Events (FTEs) on 10 November 2020, using MMS, THEMIS and Cluster spacecraft located at different magnetopause locations. Two typical scale FTE signatures are successively observed by low-latitude THEMIS, mid-latitude MMS and high latitude Cluster, reflecting their global spatial scale characteristics. Multi-spacecraft observation also revealed the complete 3-D structure of the FTEs, with azimuthal extended section, magnetosheath and magnetospheric arm. The simultaneous existence of different magnetic field line topologies during the FTEs indicates the generation mechanism of multiple X-line reconnection. Successive observations with intervals of several minutes revealed some evolutionary features of FTEs, including an increase in size and flux, and disappearance of the magnetic dip region on both sides. Our observations give a complete 3-D picture of FTEs on a global scale, which can improve our understanding of the transient magnetic reconnection and solar wind-magnetosphere interaction at the magnetopause.

We present a comprehensive analysis of magnetic and velocity fluctuations in Earth's magnetotail plasma sheet based on observations from the Magnetospheric Multiscale (MMS) mission during its 2017 magnetotail campaign. Utilizing a novel Hybrid Filter–Decision Tree Model (HFDTM), we systematically classify the plasma sheet ( X < −10 R_E in Geocentric Solar Ecliptic coordinates) into four key regions: the current sheet (CS), central plasma sheet (CPS), plasma sheet boundary layer (PSBL), and tail lobe. Within each region, we examine fluctuation dynamics across three critical flow regimes, including stagnant ( V < 50 km s −1 ), sub‐Alfvénic (50 km s −1 ≤ V < V A ), and super‐Alfvénic ( V ≥ V A ). Our key findings reveal: (a) Anisotropy Transition: Magnetic field anisotropy reverses with increasing flow speed, shifting from near‐isotropic values (Δ B ∥ /Δ B ⊥ ≈ 1.1) under stagnant conditions to strongly perpendicular‐dominated distributions (∼0.4) in the super‐Alfvénic regime; (b) Multimodal Heating: Multi‐peak structures in the thermal energy (E T ) spectrum, along with the co‐evolution of thermal (H T ) and kinetic (H V ) enstrophy from the CS to the PSBL, reveal a dual‐pathway heating mechanism involving both kinetic and magnetic energy transfer; and (c) Correlation Structure: Across all regions and regimes, weak‐to‐moderate velocity–magnetic field correlations dominate, with enhanced V ∥ ‐ B ∥ correlations under super‐Alfvénic flows. Collectively, these results identify the plasma sheet as a distinct turbulent regime, governed by localized energization mechanisms (e.g., reconnection, substorm dipolarization, and flow braking), marking a departure from the Alfvénic turbulence paradigm observed in the solar wind.

Magnetic reconnection, a fundamental energy conversion process, underpins a multitude of eruptive phenomena across the universe. Compared to the traditional standard magnetic reconnection with ion coupling, the recently discovered electron-only magnetic reconnection operates at strikingly diminutive spatial scales, imposing formidable observational constraints on resolving its intrinsic physical processes, most critically within its core region—near the X-line. Consequently, the intrinsic mechanism governing electron-only magnetic reconnection remains largely enigmatic. Leveraging high-resolution data from NASA’s MMS mission, we present unprecedented observations of two types of whistler waves in electron-only magnetic reconnection: right-handed whistler waves near the X-line, excited by perpendicular anisotropy electron distributions via second order cyclotron resonance, contrasted by left-handed whistler waves in the outflow jet. The outflow-associated whistler waves reside within a magnetic hole coupled to the Hall magnetic field. Beyond these distinct features diverging from standard magnetic reconnection, hallmark phenomena analogous to standard magnetic reconnection—specifically flux pileup region in the outflow—is also identified for the first time in this electron-only regime. Our observations may provide novel insights into the magnetic reconnection and the microscale dynamics in space and astrophysical plasmas.

Sub-ion-scale magnetic holes (MHs) are ubiquitous structures in plasmas across a wide range of environments. Despite previous observational and modeling efforts, the three-dimensional (3D) electric field in MHs has yet to be adequately resolved. In this study, utilizing high-resolution measurements of an MH (similar to 0.08 rho i x 0.14 rho i ) from the Magnetospheric Multiscale mission in Earth's turbulent magnetosheath, we report this 3D electric field and unveil its roles and generation mechanism. A model is established to quantify the impacts of E parallel to on increasing the loss cone of trapped electrons. The electric field is attributed to electron convection and pressure gradient terms of generalized Ohm's law. The MH, primarily coupling to the electron, is accompanied by electron jets. These electron jets can be interpreted as different segments of an electron vortex. These electron jets combined with nonideal electric fields not only lead to strong energy conversion ( j ( E + v e x B ) similar to 40 nW m-3) from the electromagnetic field to electrons but also enable energy conversion between different electron motion directions. Our study significantly clarifies the physical image of kinetic-scale MHs.

Driven by the scientific objective of geophysical field detection and natural hazard monitoring from space, China launched an electromagnetic satellite, which is known as the China Seismo-Electromagnetic Satellite (CSES-01), on 2 February 2018, into a circular sun-synchronous orbit with an altitude of about 507 km in the ionosphere. The CSES-01 has been in orbit for over 6 years, successfully exceeding its designed 5-year lifespan, and will continually operate as long as possible. A second identical successor (CSES-02) will be launched in December 2024 in the same orbit space. The ionosphere is a highly dynamic and complicated system, and it is necessary to comprehensively understand the electromagnetic environment and the physical effects caused by various disturbance sources. The motivation of this report is to introduce the typical electromagnetic waves, mainly in the ELF/VLF band (i.e., ~100 Hz to 25 kHz), recorded by the CSES-01 in order to call the international community for deep research on EM wave activities and geophysical sphere coupling mechanisms. The wave spectral properties and the wave propagation parameters of those typical EM wave activities in the upper ionosphere are demonstrated in this study based on wave vector analysis using the singular value decomposition (SVD) method. The analysis shows that those typical and common natural EM waves in the upper ionosphere mainly include the ionospheric hiss and proton whistlers in the ELF band (below 1 kHz), the quasiperiodic (QP) emissions, magnetospheric line radiations (MLR), the falling-tone lightning whistlers, and V-shaped streaks in the ELF/VLF band (below 20 kHz). The typical artificial EM waves in the ELF/VLF band, such as power line harmonic radiation (PLHR) and radio waves in the VLF band, are also well recorded in the ionosphere.

Based on observations from the Magnetospheric Multiscale mission, this study presents an analysis of a short large-amplitude magnetic structures (SLAMS) event with simultaneous occurrence of low- and high-frequency magnetosonic whistler waves. It was found that low-frequency magnetosonic whistler waves around the lower-hybrid frequency emerge in the presence of solar wind ions and local low-energy ions in the trailing region of SLAMS. Additionally, counter-propagating whistler waves (the high-frequency branch of the magnetosonic whistler wave) are observed within SLAMS, coinciding with a perpendicular temperature anisotropy in the electron population. Instability analyses demonstrate that these low-frequency waves are induced by the two-stream instability associated with the cross-field relative velocity between low-energy ions and electrons, while whistler waves are locally generated by the whistler anisotropy instability. Our results shed light on the impact of SLAMS on particle and wave dynamics in the terrestrial foreshock. Plain Language Summary Short large-amplitude magnetic structures (SLAMS) are frequently observed within the terrestrial foreshock. They play a significant role in particle dynamics, often leading to the formation of unstable ion and electron velocity distributions. Consequently, plasma waves are excited across both ion and electron scales. Despite their importance, direct observational evidence linking SLAMS to the local excitation of plasma waves has been lacking. In this study, we utilized observations from the Magnetospheric Multiscale mission to investigate the local excitation of magnetosonic whistler waves associated with SLAMS. We revealed the presence of counter-propagating whistler waves within SLAMS. We attributed the generation of these waves to the local whistler anisotropy instability. Furthermore, we found the occurrence of lowfrequency magnetosonic whistler waves in the trailing region of SLAMS. We identified their excitation mechanism as the two-stream instability relating to local low-energy ions. These results offer valuable insights into the intricate interplay between SLAMS and particle-wave dynamics within the terrestrial foreshock.

Turbulence is often enhanced when transmitted through a collisionless plasma shock. We investigate how the enhanced turbulent energy in the Earth's magnetosheath effectively dissipates via vortex arrays. This research topic is of great importance as it relates to particle energization at astrophysical shocks across the universe. Wave modes and intermittent coherent structures are the key candidate mechanisms for energy conversion in turbulent plasmas. Here, by comparing in-situ measurements in the Earth's magnetosheath with a theoretical model, we find the existence of vortex arrays at the transition between the downstream regions of the Earth's bow shock. Vortex arrays consist of quasi-orthogonal kinetic waves and exhibit both high volumetric filling factors and strong local energy conversion, thereby showing a greater dissipative energization than traditional waves and coherent structures. Therefore, we propose that vortex arrays are a promising mechanism for efficient energy conversion in the sheath regions downstream of astrophysical shocks.

Using a conjunction of Cluster in the mid‐altitude dayside magnetosphere and Swarm in the low‐altitude ionosphere, we show, by employing multi‐spacecraft analysis, that matched, strong magnetic perturbations and the corresponding mesoscale field‐aligned current (FAC) structures are measured in the high latitude polar cusp region during the 7 October 2015 storm. Two pairs of opposite (positive/negative) FACs are observed by both Cluster and Swarm, which may relate to pulsed magnetic reconnection at the dayside magnetopause. Furthermore, the current intensity of these matched FACs decreases from high to low latitude, consistent with the time elapsed since reconnection. Corresponding geomagnetic disturbances are also observed by ground stations. Our observations provide direct evidence for the coupling of mesoscale FACs between the magnetosphere, ionosphere and ground in the polar cusp region, where the signatures are driven in this case by conditions suitable for inducing reconnection.

The magnetic pile‐up region and its front, which plays a crucial role in electron energization during magnetic reconnection, has been widely studied at fluid and ion scales. However, there have been few studies on electron‐scale front of magnetic pile‐up regions so far. Here, we present detailed observations of electron‐scale front in a tailward reconnection exhaust. With a thickness of ∼5.5 d e (electron inertial length), the front propagated along its normal direction, mainly along the reconnection outflow direction. At this front, the strong energy conversion observed was mainly driven by the perpendicular electron current. The front can lead to adiabatic electron heating and acceleration. The front hosts an intense and highly structured electric field, reaching up to ∼120 mV/m and predominantly attributed to the electron convection term. Electrostatic waves with frequencies higher than the electron gyrofrequency and parallel normal angles (WRT background magnetic field) were detected adjacent to the front. Our study can provide insight into the roles of fronts and electron‐scale physics in magnetic reconnection.