Zhongwei Yang

Improving predictions of the geomagnetic impact of coronal mass ejections (CMEs) requires understanding how solar source properties relate to in situ measurements at Earth. However, major geomagnetic storms frequently arise from interacting CMEs, complicating the link back to their solar origins. We analyze a CME interaction event that caused a major geomagnetic storm in 2024 October 10–11 ( D _st ∼ −333 nT). Multiviewpoint observations reveal that the storm was related to a sympathetic eruption involving a quiescent filament and an active-region CME. The coronagraph on board the Advanced Space-based Solar Observatory clearly shows that this sympathetic eruption resulted in two distinct CMEs. Due to the overlap of the CMEs in the coronagraph field of view (FOV), a spheroid shock model was used to fit the observed shock. Kinematic analysis indicates that the interacting CMEs had completed their impulsive acceleration phase before entering the coronagraph FOV, with a slow deceleration continuing beyond 100 R _⊙ . In situ measurements indicate that the enhanced southward magnetic fields, arising from compression during CME interactions, were the primary driver of the storm. Compared to photospheric fields, the in situ magnetic fields suggest that the trailing CME maintained flux-rope-like signatures consistent with the source region. In contrast, the compressed leading CME displayed varying magnetic configurations between Wind and STEREO-A, featuring distorted flux-rope signatures and inconsistent inferred axis orientations. Our study bridges solar source dynamics to in situ multipoint measurements, providing key insights for space weather prediction. Nevertheless, the direct linkage between source-region magnetic field configurations and these measurements remains tentative and requires further investigation.

Magnetic reconnection is one of the most fundamental processes governing energy conversion and particle acceleration in collisionless space plasmas. Observations have revealed the occurrence of magnetic reconnection (Phan et al., 2018) and transient structures such as high-speed jets (HSJs; Hietala et al., 2009) in planetary magnetosheaths. Statistical studies based on Cluster and MMS measurements have shown that most HSJs are preferentially located downstream of the quasi-parallel bow shock (Escoubet et al., 2020). In recent years, global hybrid simulations have been extensively employed to investigate the three-dimensional global distribution of HSJs and their associated ion kinetic properties (Palmroth et al., 2021; Yang et al., 2023; Guo et al., 2024; Fatemi et al., 2024). In this study, we perform full particle-in-cell (PIC) simulations spanning spatial scales of several Earth radii and, for the first time, demonstrate an “all-in-one” multiscale kinetic scenario linking foreshock ultra low frequency (ULF) wave, non-stationary shock front (Lembege & Savoini, 1992), downstream high-speed jet (Hietala et al., 2009) and bow wave (Liu et al., 2020) formation, and the subsequent triggering of magnetic reconnections. The simulations illustrate how high dynamic-pressure structures embedded in foreshock low-frequency waves can traverse a self-reforming shock, in good agreement with MMS observations reported by Raptis et al. (2022). Furthermore, the spatial relationships among HSJs, turbulent filamentary current sheets, and reconnection sites are identified. Using the guiding-center framework commonly applied to adiabatic electron acceleration in reconnection, we quantify the relative contributions of parallel electric fields, betatron acceleration, and Fermi processes to electron energization at different stages of HSJ-driven reconnection evolution. Finally, based on our simulation results, we present a preparatory investigation for the upcoming SMILE mission (launch scheduled for 2026), discussing the penetration depth of HSJs and their induced magnetopause deformation, and providing corresponding soft X-ray images.

High-speed jets are transient structures in the magnetosheath characterized by high dynamic pressure. Their compressed magnetic field lines at the leading edge can generate bow waves, which are believed to accelerate particles and enhance energy dissipation in the magnetosheath. In this study, we analyzed a typical event within the magnetosheath, using observations from the Magnetospheric Multiscale (MMS) mission. Results reveal that during the MMS traversal of the magnetosheath, it captured for the first time a complete spatiotemporal co-occurrence of three structures: the high-speed jet, bow wave, and magnetic reconnection. Notably, the reconnection took place at the leading edge of the high-speed jet and bow wave, suggesting a potential mechanism for magnetosheath reconnection: high-speed jets propel bow waves, which then compress the pre-existing, curved magnetic field lines at the leading edge, thereby triggering reconnection. Concurrently, within the reconnection region, we observed distinct electron acceleration and heating signatures, including enhanced plasma flow, increased energy flux, and Joule dissipation. The electron characteristics exhibited significant differences between the two sides within the current sheet: on the left, the high-energy electron energy flux spectrum and pitch angle enhancements appeared only in the anti-parallel direction, whereas on the right, enhancements were observed in both parallel and anti-parallel directions. Furthermore, the electron velocity distribution function aligns with the distribution of local trapping mechanisms. These results suggest the potential existence of two different electron acceleration mechanisms during reconnection. This study reveals the coupling properties between high-speed jets and magnetosheath reconnection, providing new observational evidence for understanding how high-speed jets act as energy drivers influencing the energy transport and conversion in the magnetosheath.

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.

Kelvin–Helmholtz (KH) vortices are widely observed in astrophysics and heliophysics, including at Jovian and terrestrial magnetopauses, the Martian sheath–ionosphere boundary, the heliopause, and within stellar accretion disks. These vortices play a critical role in transporting mass, momentum, and energy across boundary layers. Magnetized planets such as Earth exhibit a higher incidence of fully rolled-up, nonlinear KH vortices compared to nonmagnetized planets like Mars. In contrast to previous magnetohydrodynamic studies, this work adopts a kinetic point of view to quantify ion mixing rates using 3D global hybrid simulations, with Earth as a representative case. This approach enables automated identification of the KH-modulated, corrugated magnetopause. For the first time, we provide a quantitative assessment of how solar wind conditions control solar wind entry and subsequent mixing with magnetospheric ions via KH waves. We find that under northward interplanetary magnetic field (IMF) conditions, the flux of particles crossing the dayside magnetopause increases with solar wind dynamic pressure and peaks in the KH region. Notably, the KH-modulated low-latitude boundary layer thins as the dynamic pressure increases. Under southward IMF conditions, coupled reconnection and KH structures further enhance solar wind injection and boost magnetospheric ion escape in the dayside, especially near the subsolar point, where reconnection intensifies this exchange. These results also shed light on the evolution of space environments and mass transport at magnetized planets in the heliosphere and beyond.

The Jovian magnetosheath provides a unique environment for examining the radial evolution of magnetosheath turbulence due to its large spatial extent. Utilizing magnetic field measurements from the Juno spacecraft, this study examines the radial evolution of magnetic field turbulence on the flanks of the Jovian magnetosheath. We find that turbulence on the dawn flank evolves significantly after crossing the bow shock. In contrast, the dusk flank exhibits a flattening of the power spectrum at MHD scales, attributed to the presence of mirror modes. Wave analysis based on the singular value decomposition method confirms the role of mirror modes in causing spectral flattening. Statistical results reinforce the connection between mirror modes and spectral flattening and reveal a dawn–dusk asymmetry in the distribution of mirror modes.

Pickup ions (PUIs) often experience acceleration and heating as they traverse interplanetary shocks, leading to the formation of a distinct suprathermal tail in their energy spectra downstream of the shock. Combining in situ observations and numerical simulations, we investigate how interplanetary shocks shape the energy spectra of PUIs in the outer heliosphere. In this study, we propose a PUI velocity distribution model by incorporating a power-law tail to account for suprathermal ions. By analyzing 18 shock events observed by New Horizons between 20 au and 45 au, we find that, after crossing the shock, the power-law index η of the suprathermal PUI energy spectrum decreases, and this decrease is positively correlated with the shock compression ratio r _c and the downstream subadiabatic index β _d . To explore the acceleration mechanism of PUIs, we conduct numerical simulations of the shock transport equation, which incorporates the three acceleration-related mechanisms (shock drift acceleration, diffusive shock acceleration, and stochastic acceleration). Our simulations show that when the perpendicular mean free path of PUIs is within 10⁻³ ∼ 10⁻² au and the velocity diffusion coefficient is within 10⁻⁹ ∼ 10⁻⁸ s⁻¹, the shock transport model can reproduce energy spectra consistent with observations. Both the observed and simulated suprathermal power-law spectra exhibit a steeper spectral profile than predictions from first-order Fermi shock acceleration theory. Most PUIs cross the shock less than three times, resulting in low acceleration efficiency, mainly due to weak spatial and velocity diffusion.

A universal method is proposed to quantify plasma exchange across the planetary magnetopause layer using the mixing rate, previously validated in local kinetic simulations of Kelvin–Helmholtz (KH) boundaries. When KH waves, magnetic reconnection, and magnetosteath jets distort the magnetopause, stationary models and the streamline method struggle to define the magnetopause surface. Using three-dimensional global hybrid simulations, we trace the solar wind and planetary ions to calculate their respective mixing rates and identify their peak distributions. A distorted magnetopause is then reconstructed through triangulation, from which local fluxes are computed across each surface element. This method supports quantitative analysis of plasma entry and escape under varying solar wind conditions and is applicable to both magnetized and unmagnetized planets.

The Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) is a joint mission of the European Space Agency (ESA) and the Chinese Academy of Sciences (CAS). Its primary objective is to investigate the Earth's magnetosphere's dynamic response to solar wind (SW) impacts through simultaneous in situ measurements of magnetosheath plasma and magnetic fields, X-ray imaging of the magnetosheath and magnetic cusps, and UV imaging of global auroral distributions. In this study, extremely magnetopause deformations associated with Hot Flow Anomalies (HFAs) are examined using a three-dimensional (3-D) global hybrid simulation. Nonuniform grids are used to enhance the resolution of the magnetosheath. Considering the parameters of SMILE's Soft X-ray Imager, we analyze the integrated soft X-ray intensity along the line-of-sight (LOS) over durations ranging from less than one minute to approximately five minutes. The simulation results demonstrate that: (1) high-speed jets (HSJs) at the leading and trailing edges of the HFA can generate X-ray intensities an order of magnitude stronger than the background magnetosheath, whereas the core region of the HFA corresponds to an X-ray dimming area; (2) a mature HFA can cause the magnetopause to expand outward by several Earth radii, exposing magnetospheric material to the solar wind ahead of the bow shock; (3) in minute-scale integrations, the HFA structure, moving from the northern to the southern hemisphere, can be discerned in the integral images within a duration of less than five minutes, while integrations lasting five minutes or longer smooth out the signal entirely. This study serves as a pre-study for the SMILE mission.

Shock drift acceleration (SDA) plays an important role in generating high-energy electrons at quasi-perpendicular shocks, but its efficiency in low-beta plasmas is questionable. In this article, we perform a two-dimensional particle-in-cell simulation of a low-Mach-number, low-plasma-beta quasi-perpendicular shock, and find that the electron cyclotron drift instability is unstable at the leading edge of the shock foot, which is excited by the relative drift between the shock-reflected ions and the incident electrons. The electrostatic waves triggered by the electron cyclotron drift instability can scatter and heat the incident electrons, which facilitates their escape from the shock’s loss cone. These electrons are then reflected by the shock and energized by SDA. In this way, the acceleration efficiency of SDA at low-plasma-beta quasi-perpendicular shocks is highly enhanced.