Aimin Du

Magnetopause flux ropes (MFRs) act as a critical mediator of solar wind–magnetosphere coupling, yet their complete global lifecycle, including generation, poleward transport, and topological collapse, remains poorly understood. We investigate this evolution with a three‐dimensional global hybrid simulation under a purely southward interplanetary magnetic field (IMF). We find that small‐scale MFRs form at low latitudes via multiple X‐line reconnections and drift poleward along the magnetopause boundary layer, driven mainly by reconnection outflows. Trailing MFRs compress leading ones, and discrete small‐scale MFRs coalesce into larger coherent structures via re‐reconnection. During poleward propagation, merged MFRs undergo coupled axial stretching induced by field‐aligned ion velocity difference and latitudinal flow difference, such that their axial extent initially expands to a maximum and then gradually contracts. As MFRs propagate toward mid‐ and high‐latitudes, magnetosheath plasma flows replace low‐latitude reconnection outflows as the necessary external driver and significantly accelerate poleward advection. Spatially inhomogeneous magnetosheath plasma flows further stretch MFRs in the dawn–dusk azimuthal direction, eroding their helical stability and inducing topological collapse. MFR helical structures therefore dissipate before reaching the magnetospheric cusp, without cusp‐mediated re‐reconnection. Our results reveal a global evolutionary pathway for dayside MFRs, in which coalescence and collapse are driven by spatially variable magnetosheath flows under purely southward IMF conditions.

We present a statistical study of Venus ionospheric variability using about two years of Pioneer Venus Orbiter measurements of the major ions O 2 + , O ⁺ , and H ⁺ during quiet solar wind conditions, solar wind high-speed streams (HSSs), and preceding corotating interaction regions (CIRs). Under quiet solar wind conditions, the dayside ionosphere is characterized by a peak O 2 + density (∼41 × 10 ⁴ cm ⁻³ ) at an altitude of ∼164 km (the V 1 layer), an O ⁺ density peak (∼71 × 10 ³ cm ⁻³ ) at ∼203 km (the V 2 layer), and an H ⁺ density peak (∼8 × 10 ² cm ⁻³ ) at ∼423 km, on average. The density of O 2 + decreases sharply below the O ⁺ density at an altitude of ∼192 km and below H ⁺ at ∼307 km. The ionosphere is characterized by prominent day–night asymmetries. The asymmetry in the peak ion densities (layer heights) is found to decrease (increase) systematically with altitude. CIRs and HSSs enhance the day–night asymmetries in the peak O 2 + and O ⁺ densities compared to their quiet time values. Considering average ionospheric parameters during the CIRs (and preceding high-density heliospheric plasma sheets), significant decreases are recorded in the dayside peak O 2 + density (∼18%), the nightside peak O ⁺ density (∼41%), the altitudes of the dayside O ⁺ (∼3%) and H ⁺ (∼19%) ion density peaks, and the dayside O 2 + /H ⁺ transition altitude (∼7%) compared to their values for the quiet ionosphere. During the HSS impacts, dayside (nightside) ionospheric O 2 + and O ⁺ peak densities exhibit decreases by ∼12% (∼64%) and ∼13% (∼44%), respectively, compared to their quiet ionospheric values. The results are discussed based on current understanding of the Venus ionospheric dynamics.

Using the gyrokinetic electron and fully kinetic ion particle simulation model, we conduct an in-depth investigation into the dynamics of magnetic reconnection in the presence of a strong guide field ( B G / B y 0 ), which is a prevalent condition in solar wind and laboratory plasmas. Here, B y 0 denotes the antiparallel component of the magnetic field, and B G represents the guide field. Our simulations explore both 2D and 3D force-free current sheets, incorporating a strong guide field ( B G / B y 0 = 5 ), a low plasma beta ( β ~ 0.02 ), and a near-realistic mass ratio ( m i / m e = 900 ). In the 2D simulations, as the mass ratio m i / m e increases, a remarkable acceleration in the formation of the primary current profile is observed. This finding highlights the substantial impact of the mass ratio on the evolution of the primary reconnection current sheet. In 3D simulations, following primary reconnection, secondary instabilities develop in the separatrix region, driven by the finite m i / m e effect. A comparative analysis of 3D and 2D results reveals that these secondary instabilities are a direct manifestation of nonlinear, 3D effects. Furthermore, the structure and growth rate of these instabilities align closely with the predictions from eigenmode theory, identifying them as ideal MHD kink modes. Notably, kinetic Alfvén waves are emitted outside the reconnection region, sharing the same wavenumber k y as the secondary instabilities, which play a crucial role in facilitating parallel electron acceleration and heating via Landau damping. These findings enhance our understanding of the intricate dynamics associated with magnetic reconnection in the presence of a strong guide field.

The West Junggar region in Xinjiang, NW China, hosts more than 100 gold deposits, most of which are shallow and nearing depletion. To assess deep mineralization potential, we integrated in situ sulfur isotope geochemistry with audio-frequency magnetotelluric (AMT) surveys at three representative deposits (Hatu, Baogutu, and Baogutu XI). Sulfide δ³⁴S values (0.46–4.16‰) indicate a deep magmatic–hydrothermal source. Petrophysical measurements reveal systematic resistivity contrasts that correlate with sulfide content. AMT surveys effectively delineate low-resistivity anomalies corresponding to mineralized zones, with persistent anomalies extending beneath known orebodies and along fault belts. These anomalies display two distinct geometric patterns: steeply dipping faults with en echelon fractures (Hatu) and S-shaped dip-transition zones (Baogutu and Baogutu XI), both reflecting structural controls on mineralization. The identified anomalies define probable mineralized zones at depth, suggesting significant undiscovered potential. This integrated geochemical and geophysical evidence provides compelling targets for deep exploration in the West Junggar region.

Hot Flow Anomalies (HFAs) are transient foreshock structures generated by solar wind discontinuity‐bow shock interactions, with their evolution only confirmed near Earth. Using MAVEN and Tianwen‐1 joint observations, we study the evolution of a Martian HFA event detected on 17 September 2022 (dayside by MAVEN, nightside by Tianwen‐1). The HFA retains a young‐type feature with negligible core magnetic fluctuations and little thickness change, but its trailing edge peak magnetic field drops by 46% (6.86–3.67 nT). We attribute the lack of young‐to‐mature evolution to Martian small bow shock, enabling HFA propagation upstream of the quasi‐perpendicular shock, precluding full development as Earth's HFAs.

Mars presently has no significant global-scale or dipole-like magnetic field from a source in the deep interior, e.g., a Martian dynamo. However, a strong remnant magnetic field was unambiguously detected above the ancient Martian crust in the southern highlands which indicating an active dynamo in past. Magnetic fields detected by orbiting satellites provided abundant crustal remnant magnetization information with a usual scale larger than ~100 km as magnetic field signals with a smaller wavelength attenuate significantly with increasing altitude. Measurements from the Martian surface (e.g., Zhurong rover and InSight lander) can provide remanent magnetic field information at smaller scales, such as the hundred meter scale. Here in this study, we investigate the crustal magnetic fields at different scales from both satellites and surface observations. The findings cover the potential formation mechanisms of large-scale magnetic stripes on Mars, the magnetic signatures of intermediate- and small-scale impact craters, and the processes of surface small-scale magnetic anomalies. The research outcomes offer supports for advancing our understanding of the evolution of the Martian magnetic fields and its habitability.

Electromagnetic ion cyclotron (EMIC) and mirror-mode (MM) waves are widely observed in terrestrial and other planetary magnetosheaths. Even though linear theory supports that EMIC and MM waves may grow at comparable rates under suitable plasma conditions, their coexistence is rarely reported within magnetosheaths, primarily due to their similar free energy source from anisotropic plasmas. Using MAVEN spacecraft data, we present the first direct in situ observations of mixed MM and EMIC waves in the Martian magnetosheath. Our observations reveal the concurrent presence of EMIC waves and MM waves, both generated in the Martian magnetosheath. Unlike in the Earth’s magnetosheath, where strong plasma compressions at the quasi-perpendicular bow shock can drive the growth of EMIC or MM waves, our results suggest that, in the Martian magnetosheath, the substantial ion anisotropy to generate EMIC and MM waves is provided by both upstream bow shock compressions and ubiquitous ion pickup processes of newborn ions. This study offers new insights into the role of ion pickup processes in the excitation and growth of EMIC and MM waves within planetary magnetosheaths, particularly in magnetosheaths where both shock heating and newborn ion pickup processes provide the prevailing anisotropic plasma environment, as seen in the magnetosheaths of Venus, Mars, and comets.

High‐intensity long‐duration continuous auroral electrojet activity (HILDCAA) events caused by interplanetary Alfvén waves are associated with global‐scale convection events. HILDCAAs occur primarily during the solar cycle declining phase (Hajra et al., 2013, https://doi.org/10.1002/jgra.50530 ). A statistical study is conducted for 42 HILDCAAs occurring between 2009 and 2023 to investigate associated auroral region field‐aligned currents (FACs). The FAC measurements used in this study were made by the Active Magnetosphere and Planetary Electrodynamics Response Experiment. It is shown that HILDCAA‐related FAC probability distributions are characterized by a median FAC intensity of ∼5 MA, ∼2 times the quiet time FAC intensity, with slight variations between day and night, and from one season to the other. During HILDCAAs (pre‐HILDCAA quiet times), the dayside FAC intensity is found to be the strongest during summer, ∼15%–32% (∼92%–96%) stronger than during equinoxes, and ∼87% (∼128%) stronger than during winter. The nightside HILDCAA‐related FAC intensity during fall is found to be ∼8%, ∼10%, and ∼29% stronger than during summer, spring, and winter, respectively. For pre‐HILDCAA intervals, the nightside FAC intensity during summer is ∼51%, ∼62%, and ∼94% stronger than during fall, winter, and spring, respectively. These latter results are in clear contrasts to previous results showing no seasonal dependences of nightside FAC intensities during geomagnetic quiet and disturbed times.

Enhanced solar wind‐magnetosphere energy coupling during geomagnetic disturbances leads to strong geomagnetic field‐aligned currents (FACs). While variations of FACs during geomagnetic storms and substorms have been well explored, there is no systematic study of FACs during high‐intensity long‐duration continuous auroral electrojet activities (HILDCAAs). Substorm studies usually involve the quiet solar wind and storm studies typically involve interplanetary coronal mass ejections and their sheaths, while HILDCAAs typically involve high‐speed streams. Here we present, for the first time, a statistical study of HILDCAA‐related FAC variation based on measurements by the Active Magnetosphere and Planetary Electrodynamics Response Experiment from 2009 through 2023. During HILDCAAs, FACs are found to extend in a large region, from the pole down to ∼65° magnetic latitude, with a characteristic peak intensity ∼5 times the quiet time FAC intensity. The FAC intensity variation is characterized by periodicities of ∼19 and ∼11 hr (in descending order of spectral power), well correlated to the auroral electrojet current westward component SML. On average, the HILDCAA‐related FAC variation is delayed from the Alfvén wave interplanetary magnetic field B _z component fluctuations by ∼28 ± 17 min. The HILDCAA onset is marked by a sharp increase in average FAC intensity temporal profile, peaking ∼14 hr after the HILDCAA onset time. The HILDCAA‐related FAC intensification is found to be associated with enhanced magnetic flux opening and energy transfer at the dayside magnetopause. The results are consistent with FAC relationships with solar wind variations and geomagnetic conditions reported previously for geomagnetic storms and substorms.

Flux ropes (FRs), ubiquitous helical magnetic structures in solar system plasmas, are important to energy and particle transport. At Mars, where global intrinsic magnetic fields are absent, FRs form through magnetic reconnection (MR) and magnetospheric or ionospheric boundary wave instabilities (BWIs), but their role in ion escape remains controversial. Here, we first present the global distribution of MR‐ and BWI‐FRs from Martian ionosphere to magnetosheath, utilizing 4,012 FR events identified from 5‐year observations by the Mars Atmosphere and Volatile EvolutioN (MAVEN) satellite. We find that the global occurrence rate of FRs associated with BWIs is comparable with those from MR. Enhanced oxygen ion outflow fluxes and densities within most nightside BWI‐FRs suggest they predominantly originate from the dayside ionosphere/magnetosphere. These BWI‐FRs have sufficient magnetic field intensity to carry oxygen ions beyond escape energies, suggesting their potential role in facilitating global ion escape from Mars via magnetotail transport.