The presented work examines the extreme geomagnetic storm that occurred during May 10–12, 2024, following solar flares on May 8–9, 2024, hence named the Victory Day Storm. This event, marked as the most intense geomagnetic storm of the 21st century to date, caused significant disturbances not only in the auroral zone but also in the subauroral and mid-latitude ionosphere. Using data from satellites, ground-based ionosondes, Global Navigation Satellite System (GNSS) receivers, and all-sky cameras located in the Kaliningrad region, this research tracks how the coronal mass ejection from the Sun led to substantial changes in ionospheric plasma density, structure, and dynamics. Notably, auroras were observed in the subauroral and mid-latitudes, which is a rare phenomenon at these latitudes, providing valuable information on the ionospheric response to extreme geomagnetic activity. Swarm and DMSP satellite data identified polarization jet/SAID as U-shaped structures on ionograms, while Strong Thermal Emission Velocity Enhancements (STEVE) was observed by an all-sky camera along with increased Rate of Total Electron Content Index (ROTI). A diffuse aurora with a moving omega structure, as well as ray and corona auroral features, were observed, accompanied by a significant ROTI increase and enhanced scattering of the auroral Es layer on ionograms.

Abstract Auroral substorms that move from auroral (<70°) to polar (>70°) magnetic latitudes (MLAT) are known to occur preferentially when a high‐speed solar wind stream passes by Earth. We report here on observations that occurred during a ∼75‐min interval with high‐speed solar wind on 28 November 2022 during which auroral arcs and very large geomagnetic disturbances (GMDs), also known as magnetic perturbation events (MPEs), with amplitude >9 nT/s = 540 nT/min moved progressively poleward at eight stations spanning a large region near and north of Hudson Bay, Canada shortly before midnight local time. Sustained GMD activity with amplitudes >3 nT/s appeared at each station for durations from 13 to 25 min. Spherical Elementary Currents Systems maps showed the poleward movement of a large‐scale westward electrojet as well as mesoscale electrojet structures and highly localized up/down pairs of vertical currents near these stations when the largest GMDs were observed. This study is consistent with other recent studies showing that very large poleward‐progressing GMDs can occur under high Vsw conditions, but is the first to document the sustained occurrence of large GMDs over such a wide high‐latitude region.

Abstract Interchange instability is a macroscopic instability that commonly develops when the centrifugal acceleration opposes the acceleration induced by the density gradient at the interface between two regions. Over the past two decades, extensive studies have focused on this instability, particularly at dipolarization fronts. However, due to the similar physical properties of these two boundary layers, it has also been implicated that this instability may develop at the magnetopause (W. D. Fu, Fu, Cao, et al., 2025, https://doi.org/10.1029/2025ja033633). In this work, we analyze data from the Magnetospheric Multiscale (MMS) mission to identify a series of quasi‐periodic magnetic field disturbances during a subsolar magnetopause crossing event. Alongside these magnetic field disturbances, the magnetospheric plasma population alternated with the magnetosheath population. By examining solar wind conditions and performing the timing analysis, we confirmed that these observations were not due to temporal variations from inward or outward motions of the magnetopause, but rather corresponded to spatial magnetic field structures. We further demonstrate that these structures do not meet the criterion for mirror mode, but instead fulfill the unstable condition for the interchange mode, revealing that such structures were formed by the interchange instability. This discovery offers new insights into the plasma exchange between the magnetosphere and solar wind, and opens promising avenues for further exploration with the upcoming Solar‐Wind‐Magnetosphere‐Ionosphere Link Explorer (SMILE) mission through its global‐scale imaging.

Abstract The dipolarization front (DF), as the leading edge of bursty bulk flows, is typically seen as the boundary between the cold‐dense current sheet plasma and the hot‐tenuous reconnection outflow plasma. This interface plays an analogous role to the magnetopause, which separates the cold‐dense magnetosheath plasma from the hot‐tenuous magnetosphere plasma. In this study, we compare the typical characteristics of these two interfaces from the Magnetospheric Multiscale mission observations, revealing several similarities in their plasma environments, ion‐scale properties, and kinetic processes. These similarities implicate that some other MHD processes, such as interchange instability, may also develop at the subsolar magnetopause, similar to their occurrence at the leading edge of the DF. Furthermore, the flanks of the DF may be susceptible to Kelvin–Helmholtz instabilities, similar to those observed at the magnetopause flanks. These implications present promising opportunities for further investigation with the upcoming Solar‐Wind‐Magnetosphere‐Ionosphere Link Explorer mission through its global‐scale imaging.

Abstract Over the past 6 decades, Kelvin–Helmholtz (K–H) vortices, arising from quasi‐viscous flow velocity shear on the flanks of the magnetopause, have been extensively studied and are recognized as a key pathway for solar wind entry into the magnetosphere. Recent research by W. D. Fu et al. (2025a, (https://doi.org/10.1029/2025ja033633), 2025b), (https://doi.org/10.1029/2025ja033894) has shown that the magnetopause and dipolarization front share many similar characteristics, implying that such instabilities could also be triggered on the flanks of dipolarization fronts. Here, we report a DF crossing event observed by the Magnetospheric Multiscale (MMS) mission, during which the spacecraft traversed from the dawnside flank of the front. Electron flow vortices were detected at the boundary, which are confirmed to result from electron K–H instability, developed by velocity shear in the electron flows. Using the FOTE‐V method, we reconstruct the local velocity topology and identify a vortex with a characteristic scale of ∼6 de, in agreement with theoretical predictions. These results provide direct evidence for electron K–H instability at the DF flanks, unveiling a new layer of complexity in boundary dynamics and offering a powerful window for studying these fundamental instabilities across different scales.

Abstract 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 < VA), and super‐Alfvénic (V ≥ VA). Our key findings reveal: (a) Anisotropy Transition: Magnetic field anisotropy reverses with increasing flow speed, shifting from near‐isotropic values (ΔB∥/ΔB⊥ ≈ 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 (ET) spectrum, along with the co‐evolution of thermal (HT) and kinetic (HV) 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.

Future planetary exploration missions will rely heavily on efficient human-robot interaction to ensure astronaut safety and maximize scientific return. In this context, digital twins offer a promising tool for planning, simulating, and optimizing extravehicular activities. This study presents the development and evaluation of a digital twin for the AMADEE-24 analog Mars mission, organized by the Austrian Space Forum and conducted in Armenia in March 2024. Alternative local positioning methods were evaluated to enhance the system's utility in Global Navigation Satellite System (GNSS)-denied environments. The digital twin integrates telemetry from the Aouda space suit simulators, inertial measurement unit motion capture (IMU-MoCap), and sensor data from the Intuitive Rover Operation and Collecting Samples (iROCS) rover. All nine experiment runs were reconstructed successfully by the developed digital twin. A comparative analysis of localization methods found that Simultaneous Localization and Mapping (SLAM)-based rover positioning and IMU-MoCap localization of the astronaut matched Global Positioning System (GPS) performance. Adaptive Cluster Detection showed significantly higher deviations compared to the previous GNSS alternatives. However, the IMU-MoCap method was limited by discontinuous segment-wise measurements, which required intermittent GPS recalibration. Despite these limitations, the results highlight the potential of alternative localization techniques for digital twin integration.

We investigate small-scale magnetic energy generation in a turbulent conducting flow using two different approaches. One is based on the Kazantsev-Kraichnan (KK) model, developed for a random velocity field with short time correlations, and the other uses the shell magnetohydrodynamic (MHD) method, which describes a turbulent energy cascade on a finite number of spectral shells. We consider only the kinematic (linear) regime and show an exponential growth of magnetic energy for sufficiently large magnetic Reynolds numbers (Rm) in both approaches. By comparing the dependencies of the growth rates at different Rm, we try to answer the question how the model assumptions-of short time correlations or of finite spectral shells-affect the turbulent dynamo possibility and the position of the Rm threshold at which this generation starts. We analyze the generation behavior at different Reynolds and magnetic Prandtl numbers, which are not explicitly included in the KK model but taken into account in the shell approach. Based on the obtained results, we try to discuss why the small-scale generation has not been observed in real MHD dynamo experiments so far.

Abstract We present multiband observations and analysis of EP240801a, a low-energy, extremely soft gamma-ray burst (GRB) discovered on 2024 August 1 by the Einstein Probe (EP) satellite with a weak contemporaneous signal also detected by the Fermi Gamma-ray Burst Monitor (GBM). Optical spectroscopy of the afterglow, obtained by Gran Telescopio Canarias and Keck, identified the redshift of z = 1.6734. EP240801a exhibits a burst duration of 148 s in X-rays and 22.3 s in gamma rays, with X-rays leading by 80.61 s. Spectral lag analysis indicates that the gamma-ray signal arrived 8.3 s earlier than the X-rays. Joint spectral fitting of EP Wide-field X-ray Telescope and Fermi/GBM data yields an isotropic energy E γ , iso = ( 5.5 7 − 0.50 + 0.54 ) × 1 0 51 erg , a peak energy E peak = 14.9 0 − 4.71 + 7.08 keV , and a fluence ratio S(25–50 keV)/S ( 50 – 100 keV ) = 1.6 7 − 0.46 + 0.74 , classifying EP240801a as an X-ray flash (XRF). The host-galaxy continuum spectrum, inferred using Prospector, was used to correct its contribution for the observed outburst optical data. Unusual early R-band behavior and EP Follow-up X-ray Telescope observations suggest multiple components in the afterglow. Three models are considered: a two-component jet model, a forward-reverse shock model, and a forward shock model with energy injection. All three provide reasonable explanations. The two-component jet model and the energy injection model imply a relatively small initial energy and velocity of the jet in the line of sight, while the forward-reverse shock model remains typical. Under the two-component jet model, EP240801a may resemble GRB 221009A (BOAT) if the bright narrow beam is viewed on-axis. Therefore, EP240801a can be interpreted as an off-beam (narrow) jet or an intrinsically weak GRB jet. Our findings provide crucial clues for uncovering the origin of XRFs.