Scientific publications

2026

• Active chromospheric fibril singularity
  
  • Joshi Reetika
  • Rouppe van der Voort Luc
  • Aulanier Guillaume
  • Danilovic Sanja
  • Prasad Avijeet
  • Díaz Baso Carlos
  • Nóbrega-Siverio Daniel
  • Poirier Nicolas
  • Calchetti Daniele
  Astronomy & Astrophysics - A&A, EDP Sciences, 2026, 706, pp.A369. Context. The fine structures of the solar chromosphere, driven by photospheric motions, play a crucial role in the dynamics of solar magnetic fields. Many such structures have already been identified, such as fibrils, filament feet, and arch filament systems. Nevertheless, high-resolution observations show a wealth of structures whose nature remains elusive. Aims. We observed a puzzling, unprecedented chromospheric fibril singularity in the close vicinity of a blow-out solar jet and a flaring loop. We aim to understand the magnetic nature of this singularity and the cause of its activity using coordinated high-resolution, multi-wavelength observations. Methods. We aligned datasets from Solar Orbiter, SST, IRIS, and SDO. We re-projected the Solar Orbiter datasets to match the perspective of the Earth-based instruments and performed potential field extrapolations from Solar Orbiter/PHI data. We analysed the spatial and temporal evolution of the plasma structures and their link with the surface magnetic field. This led us to derive a model and scenario for the observed structures, which we explain in a general schematic representation. Results. We have discovered a new feature: a singularity in the chromospheric fibril pattern. It forms in a weak magnetic-field corridor between two flux concentrations of equal sign, at the base of a vertically inverted-Y-shaped field-line pattern. In this specific case, some activity develops along the structure: first, a flaring loop at one end, and second, a blow-out jet at the other end, where a coronal null point was present and associated with a chromospheric saddle point located on the fibril singularity. The observations suggest that both active phenomena are initiated by converging photospheric moat flows that exert pressure on this fibril singularity. (10.1051/0004-6361/202556666)
  DOI : 10.1051/0004-6361/202556666
• Flux rope formation through flux cancellation of sheared coronal arcades in a 3D convectively driven MHD simulation
  
  • Furuseth S.
  • Aulanier Guillaume
  Astronomy & Astrophysics - A&A, EDP Sciences, 2026, 706, pp.A350. Context. Space weather and its potential negative consequences for life on Earth have received increasing scientific attention in recent decades. In particular, predicting the onset of coronal mass ejections (CMEs) has become important from a security perspective. To predict CMEs, one must first understand the dynamics leading to preeruptive magnetic field configurations, which in many theories include a flux rope. Aims. In this study, we investigate the realistic formation of coronal flux ropes above the solar photosphere. The aim is to find out if and how flux ropes can form there, and how the formation is related to flux cancellation at the photosphere. Previously, such formation has been shown in smooth boundary-driven line-tied simulations and in idealized non-convective and symmetric flux-emergence simulations. Methods. We ran a convective nonsymmetric 3D radiative magnetohydrodynamic (MHD) simulation with the code Bifrost . Within the simulation box of 24 Mm × 24 Mm horizontal extent, a linear force-free field with sheared coronal arcades was slowly inserted. Following the insertion, the self-consistent stochastic plasma flows of the convection zone drove several small-scale flux cancellations and magnetic reconnection, without external influence. Lagrangian markers called corks were used to track the dynamic evolution of the magnetic field. Results. Over a period of 2.5 h, a flux rope was generated with photospheric footpoints separated by up to 12 Mm. The flux rope was gradually formed through several individual events, such as slipping reconnection, U-loop emergence, and thick-photosphere tether-cutting reconnection. Conclusions. Flux ropes, which can lead to CMEs, can be formed in the solar atmosphere solely driven by convection and flux cancellations at the photosphere. However, not all flux cancellations contribute to the buildup of the flux rope, and some coronal reconnection events that do are not clearly related to flux cancellation. The formation process of flux ropes from coronal sheared arcades driven by convection is therefore more complex than in the original smooth flux cancellation model. However, the end result is qualitatively the same. Flux cancellation works. A flux rope is formed. (10.1051/0004-6361/202554242)
  DOI : 10.1051/0004-6361/202554242
• Formation of gradients of atomic oxygen in nanosecond plasma for plasma-assisted detonation: experimental and numerical study
  
  • Lafaurie Victor
  • Shu Zhan
  • Zhang B
  • Terentjeviene M
  • Billeau Jean-Baptiste
  • Orel Inna
  • Hoyos Aristizabal Samuel
  • Vidal Pierre
  • Starikovskaia Svetlana
  Plasma Sources Science and Technology, IOP Publishing, 2026, 35 (2), pp.025022. This work aims at producing a gradient of atomic oxygen on a scale of 10 cm in a plane-to-plane nanosecond discharge in 150 mbar of air with a varying gap size for applications in combustion and ignition of detonation waves. Local measurements of atomic oxygen density along the discharge span, at varying heights between high-voltage and grounded electrode, are performed with Xe calibrated O-TALIF and validated by 2D numerical modelling. They both show existence of a gradient of atomic density of oxygen along the span. Reduced electric field is measured with two experimental techniques: optical emission spectroscopy by a spectral band intensity ratio of the first negative system and the second positive system of nitrogen, and E-FISH. It is also compared with numerical modelling. All techniques show existence of a gradient of reduced electric field along the span. This distribution of reduced electric field, in combination with the non-uniform energy deposition in the plasma, is shown to explain the measured gradient of density of atomic oxygen. (10.1088/1361-6595/ae3f53)
  DOI : 10.1088/1361-6595/ae3f53
• Spectral Properties and Energy Injection in Mercury's Magnetotail Current Sheet
  
  • Li Xinmin
  • Dong Chuanfei
  • Wang Liang
  • Aizawa Sae
  • Hadid L. Z.
  • Zhang Chi
  • Zhou Hongyang
  • Slavin James
  • Gao Jiawei
  • Stumpo Mirko
  • Zhang Wei
  Geophysical Research Letters, American Geophysical Union, 2026, 53 (4). Abstract Mercury's magnetotail hosts a thin and highly dynamic current sheet (CS), where magnetic reconnection and strong fluctuations frequently occur. Here, we statistically analyze magnetic field power spectra across 370 magnetotail CSs observed by MESSENGER. About 20% of the events are quasi‐laminar, showing single power‐law spectra, whereas ∼80% are turbulent, exhibiting a spectral break separating inertial and kinetic ranges. A dawn–dusk asymmetry is identified: inertial‐range slopes are systematically shallower on the dawnside, whereas kinetic‐range slopes are steeper, indicating more developed turbulence there, consistent with the higher occurrence of reconnection‐related processes on the dawnside. Component analysis shows that the transverse components, orthogonal to the tail‐aligned principal field ( B X ), display shallow slopes near −1 in the inertial range, suggesting energy injection at ion scales rather than a classical inertial range. These results demonstrate that Mercury's unique plasma environment fundamentally reshapes the initiation of turbulence and the redistribution of energy in the magnetotail. (10.1029/2025GL120144)
  DOI : 10.1029/2025GL120144
• Benchmark for two-dimensional large scale coherent structures in partially magnetized E × B plasmas—community collaboration & lessons learned
  
  • Powis Andrew T
  • Ahedo Eduardo
  • Álvarez Laguna Alejandro
  • Barléon Nicolas
  • Bello-Benítez Enrique
  • Beving Lucas
  • Boeuf Jean-Pierre
  • Bogopolsky Guillaume
  • Bourdon Anne
  • Cichocki Filippo
  • Cuenot Bénédicte
  • Denig Andrew
  • Donkó Zoltán
  • Elias Paul-Quentin
  • Encinar Miguel
  • Eremin Denis
  • Fajardo Pablo
  • Faraji Farbod
  • Fubiani Gwenael
  • Garrigues Laurent
  • Hara Kentaro
  • Hartmann Peter
  • Hopkins Matthew
  • Kaganovich Igor D
  • Knoll Aaron
  • Lapenta Giovanni
  • Magin Thierry
  • Marín-Cebrián Alberto
  • Merino Mario
  • Minelli Pierpaolo
  • Papahn Zadeh Mina
  • Parodi Pietro
  • Petronio Federico
  • Reza Maryam
  • Smolyakov Andrei I
  • Sydorenko Dmytro
  • Taccogna Francesco
  • Turner Miles M
  • Vermorel Olivier
  • Villafana Willca
  • Xu Liang
  Plasma Sources Science and Technology, IOP Publishing, 2026, 35 (2), pp.025002. Abstract Low-temperature plasmas (LTPs) are essential to both fundamental scientific research and critical industrial applications. As in many areas of science, numerical simulations have become a vital tool for uncovering new physical phenomena and guiding technological development. Code benchmarking remains crucial for verifying implementations and evaluating performance. This work continues the Landmark benchmark initiative, a series specifically designed to support the verification of LTP codes. In this study, seventeen simulation codes from a collaborative community of nineteen international institutions modeled a partially magnetized E × B Penning discharge. The emergence of large scale coherent structures, or rotating plasma spokes, endows this configuration with an enormous range of time scales, making it particularly challenging to simulate. The codes showed excellent agreement on the rotation frequency of the spoke as well as key plasma properties, including time-averaged ion density, plasma potential, and electron temperature profiles. Achieving this level of agreement came with challenges, and we share lessons learned on how to conduct future benchmarking campaigns. Comparing code implementations, computational hardware, and simulation runtimes also revealed interesting trends, which are summarized with the aim of guiding future plasma simulation software development. (10.1088/1361-6595/ae3985)
  DOI : 10.1088/1361-6595/ae3985
• Cold atmospheric plasma promotes migration persistence, through induced H2O2 and electric field
  
  • Labérie Benjamin
  • Saugé Louis
  • Polesskaya Anna
  • Rousseau Antoine
  • Gautreau Alexis M
  Biophysical Journal, Biophysical Society, 2026, 125 (3), pp.697-708. Cold atmospheric plasma (CAP) generates various products, including radiation, electrons, ions, an electric field, and reactive oxygen and nitrogen species. CAP promotes wound healing and has been implemented in several medical devices to treat acute or chronic wounds. Beyond the closure of the epidermal monolayer of keratinocytes, wound healing requires migration of dermal fibroblasts. The effect of CAP on fibroblast migration has been insufficiently characterized. Here, we show, using primary human dermal fibroblasts, that a 10-s exposure to CAP suffices to increase Arp2/3-dependent lamellipodium formation and migration persistence for several hours. In an attempt to identify the specific CAP-generated products involved in this activity, we found that reactive oxygen species and the electric field induced by plasma were critical for enhanced and sustained migration persistence. Taken separately, these two stimuli were only partially active in inducing migration persistence at the dose that CAP generates. However, their combination was sufficient to recapitulate the full enhancement of migration persistence obtained with CAP exposure, indicating that these two stimuli act in synergy and that they likely represent the active components of CAP to activate migration of dermal fibroblasts during wound healing. (10.1016/j.bpj.2025.11.2685)
  DOI : 10.1016/j.bpj.2025.11.2685
• Evidence of an Extended Alfvén Wing System at Enceladus: Cassini's Multi‐Instrument Observations
  
  • Hadid Lina Z.
  • Chust Thomas
  • Wahlund Jan-Erik
  • Morooka Michiko W
  • Roussos Elias
  • Witasse Olivier
  • Rabia Jonas
  • Pisa David
  • Kim Konstantin
  • Edberg Niklas J T
  • Rymer Abigail M
  • Lamy Laurent
  • Kotsiaros Stavros
  • Aizawa Sae
  • Jeandet Alexis
  • Modolo Ronan
  • André Nicolas
  • Canu Patrick
  • Bowers Charles F
  • Jia Xianzhe
  • Coates Andrew J
  • Jones Geraint H
  • Parsec‐wallis Anna
  • Agiwal Omakshi
  • Holmberg Mika K G
  • Nénon Quentin
  • Cao Hao
  • Kurth William S
  • Dougherty Michele K
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2026, 131 (2). We report in situ evidence for Enceladus' Alfvén wing system and its coupling with Saturn's ionosphere, based on multi-instrument observations from the Cassini spacecraft. Analysis of 36 events, including 13 from non-flyby paths, confirms the existence of a Main Alfvén Wing (MAW) current system generated at Enceladus, and associated Reflected Alfvén Wings (RAWs) occurring both at Saturn's ionosphere and on the density gradient of Enceladus' plasma torus, extending longitudinally to at least ∼ 120°(∼2,000 moon radii) downstream of the moon. Additionally, the observations reveal the systematic existence of a filamentation process of these large-scale Alfvénic perturbations (MAW and RAWs) during their propagation at any distance from their source. These findings demonstrate a more extensive electrodynamic coupling than previously reported for Enceladus and more generally for any moon-magnetosphere interaction. Moreover, the observation of energetic electron depletions and water-group ion signatures at longitudes even further from the moon supports the interpretation of an extended and persistent interaction region. These results highlight Enceladus' role in shaping Saturn's magnetospheric environment and underscore the importance of future missions to exhaustively analyze this type of complex interaction between a moon and a planet. Plain Language Summary Saturn's small icy moon Enceladus interacts with the planet's magnetic field, generating intermittent aurora in Saturn's upper atmosphere and electromagnetic waves that travel along invisible magnetic connections between them. During its 13-year mission, the Cassini spacecraft repeatedly crossed these magnetic field lines linked to Enceladus. We used data from several Cassini instruments to study how energy and particles move between the moon and Saturn. We detected wave activity characteristic of Alfvén waves (similar to vibrations on a string), forming as Saturn's magnetic field flows past Enceladus. Due to a complex system of reflection at both Saturn's ionosphere and the boundary of Enceladus' torus, these waves were found not only near the moon but also trailing far behind it, extending more than 504,000 km (over 2,000 times the moon's radius) behind it. This is the first time that Alfvén waves have been observed to be directly linked to the charged particles associated with Enceladus. This shows that Enceladus plays a much bigger role in shaping Saturn's space environment than previously thought, and reveals how moons can influence their host planet across vast distances. (10.1029/2025ja034657)
  DOI : 10.1029/2025ja034657
• High-order moment closure for nonmagnetized electrons in partially ionized plasmas
  
  • Alvarez Laguna A.
  • Hara K.
  Physical Review E, American Physical Society (APS), 2026, 113 (2), pp.025207. Linearized moment equations are often used to derive closure models for the hydrodynamic equations of multi-component plasmas near thermodynamic equilibrium. However, the linearized transport equations lose their validity in rarefied conditions or in the presence of strong electric fields, when the velocity distribution functions (VDFs) of the different species are non-Maxwellian and the drift between the species, i.e., the Mach number of the relative motion, becomes large. In this paper, we develop a nonlinear, high-order moment model for nonmagnetized electrons in partially ionized plasmas. We present a fourteen-moment model using a Hermitian expansion of the VDF that considers density, momentum, anisotropic pressure tensor, contracted heat flux vector, and contracted scalar kurtosis. We consider the relevant collisional processes in partially ionized plasmas, such as elastic and inelastic electron-neutral, electron-impact ionization, electron-electron Coulomb, and electron-ion Coulomb collisions. The collisional terms in the electron moment equations are integrated analytically for finite Mach numbers and accounting for the nonlinear terms in the Boltzmann operator, which are often neglected in linearized closure models. The proposed closure presents novel cross-coupling effects between moments of different tensorial nature within the collisional terms. The present nonlinear fourteen-moment model is benchmarked against a Monte Carlo simulation under a spatially homogeneous configuration, showing good agreement for a wide range of reduced electric field (e.g., up to 1000 Td) before runaway electrons occur, improving the results of a linear fourteen-moment model. (10.1103/lm1z-bzt3)
  DOI : 10.1103/lm1z-bzt3
• Magnetic reversals in a geodynamo model with a stably–stratified layer
  
  • Müller Nicolás P
  • Gissinger Christophe
  • Pétrélis François
  Physics of the Earth and Planetary Interiors, Elsevier, 2026, 371, pp.107502. We study the process of magnetic reversals in the presence of a stably-stratified layer below the core-mantle boundary using direct numerical simulations of the incompressible magnetohydrodynamics equations under the Boussinesq approximation in a spherical shell. We show that the dipolar-multipolar transition shifts to larger Rayleigh numbers in the presence of a stably-stratified layer, and that the dipolar strength of the magnetic field at the core-mantle boundary increases due to the skin effect. By imposing an heterogeneous heat flux at the outer boundary, we break the equatorial symmetry of the flow, and show that different heat flux patterns can trigger different dynamo solutions, such as hemispheric dynamos and polarity reversals. Using kinematic dynamo simulations, we show that the stably-stratified layer leads to similar growth rates of the dipole and quadrupole components of the magnetic field, playing the role of a conducting boundary layer, favouring magnetic reversals, and a dynamics predicted by low-dimensional models. (10.1016/j.pepi.2026.107502)
  DOI : 10.1016/j.pepi.2026.107502
• Shock-induced magnetic reconnection driving Ellerman bomb emission and a spicule
  
  • Sand Mats Ola
  • Noraz Quentin
  • Aulanier Guillaume
  • Martínez-Sykora Juan
  • Carlsson Mats
  • Rouppe van der Voort Luc
  Astronomy & Astrophysics - A&A, EDP Sciences, 2026, 705, pp.A205. Context. The formation mechanism for the dynamic type II spicules has remained elusive for many years. Their dynamical behaviour has long been linked to magnetic reconnection, yet no conclusive evidence has been provided. However, one recent observational study found signs of magnetic reconnection, as traced by Ellerman bombs (EBs), at the footpoints of many spicules. The triggering of EBs is generally linked to magnetic reconnection due to flux emergence and convective motions in the photosphere. Aims. We aim to explore whether we can connect EBs to type II spicules, and determine to what extent we can use EBs as an observational proxy to probe magnetic reconnection in this dynamic. We also aim to provide further insight into the mechanisms that trigger EBs. Methods. We used a simulation run with the radiative magnetohydrodynamics code Bifrost to track spicules and study the physical processes underlying their formation. To detect EBs and classify the spicules, we synthesised the chromospheric H α spectral line using the multilevel radiative transfer code RH1.5D. We also traced shocks and current sheets to decipher the origin of EBs and spicules. We selected one type II spicule with a strong EB near its footpoint and studied their formation in detail. Results. A magnetoacoustic shock advects the magnetic field lines towards an oppositely directed ambient field, creating a current sheet. The current sheet accelerates dense plasma via a whiplash effect generated by magnetic reconnection into the inclined ambient field, launching the spicule. Several EB profiles trace shock- and magnetic-reconnection-induced dynamics during this process at the spicule footpoint. Conclusions. We present a new EB triggering mechanism in which a shock-induced current sheet reconnects, triggering an EB in the lower solar atmosphere. The shock-induced current sheet generates the upwards propagation of a type II spicule via reconnection outflows. These results provide a plausible physical origin for the recently observed connection between EBs and spicules. (10.1051/0004-6361/202557602)
  DOI : 10.1051/0004-6361/202557602
• Chromosphere of the quiet sun: I. Shock and current-sheet dynamics and heating
  
  • Noraz Q.
  • Carlsson M.
  • Aulanier Guillaume
  Astronomy & Astrophysics - A&A, EDP Sciences, 2026, 705, pp.A86. Context. The solar chromosphere is a dynamic and crucial interface between the solar interior and its interplanetary environment, regulating how energy is locally deposited into heat and transported into the upper atmospheric layers. Despite significant observational and theoretical progress, the dominant processes responsible for chromospheric heating remain debated, particularly under quiet-Sun (QS) conditions. Aims. We aim to disentangle and quantify the respective roles of shocks and current sheets (CSs) in QS chromospheric modelling. Methods. We use a convection-zone-to-corona simulation performed with the radiation-magnetohydrodynamics code Bifrost . In order to identify shocks and CS events across space and time, we develop and apply physics-based criteria, allowing us to describe their dynamics and evaluate their contributions to both dissipative (viscous and ohmic) and mechanical (including compressive work) heating. Results. Shocks are found to dominate the energy deposition in the lower chromosphere (1 ≲ z ≲ 1.5 Mm), accounting for up to 59% of the mechanical heating rate near z = 1.2 Mm. In contrast, CSs become the primary contributor in the upper chromosphere (1.5 ≲ z ≲ 2.5 Mm), as both plasma β and Mach number Ma drop. Overall, 66% of the mechanical chromospheric heating is powered by the combined action of shocks and CSs, with 13% emerging from regions where shocks and CSs overlap, underscoring the pivotal role of dynamic coupling in the chromosphere. Conclusions. These results support a multi-process view of chromospheric heating in the QS, dominated by shocks, CSs, and non-steep gradient dynamics. In addition to viscous and ohmic dissipation, compressive heating can play a major role locally in the model, particularly in chromospheric shock structures, where it non-reversibly offsets cooling from expansion and radiation, and therefore constitutes a key heating contribution to consider in the energy budget. This study further highlights the need for next-generation observations to resolve the intermittent and small-scale nature of chromospheric dynamics, in order to bring new constraints on the coupling between the different layers of the solar atmosphere. (10.1051/0004-6361/202556375)
  DOI : 10.1051/0004-6361/202556375
• Cold atmospheric plasma mediates antibiofilm activity and sensitization to further plasma and antibiotic challenges against Staphylococcus aureus
  
  • Capuzzo Elena
  • Mas Fiol Guillem
  • Cayet Nadège
  • Varet Hugo
  • Pizarro-Cerda Javier
  • Frescaline Nadira
  • Rousseau Antoine
  • Dussurget Olivier
  FEMS Microbes, Oxford University Press, 2026, 7, pp.xtag039. Staphylococcus aureus biofilms pose significant challenges in clinical settings due to their growing resistance to conventional antibiotics. While cold atmospheric plasma (CAP) is known for its bactericidal effects, its impact on biofilm architecture and physiology, and subsequent antimicrobial susceptibility remains poorly understood. This study investigates the effects of CAP treatment on S. aureus biofilms. We demonstrate that CAP not only reduces biofilm but also disrupts biofilm architecture and alters bacterial cell morphology. Transcriptomic analysis reveals distinct gene expression profiles following treatments with CAP and hydrogen peroxide, one of its active components, highlighting unique stress responses. We further show that CAP treatment of S. aureus grown on agar plates sensitizes bacteria to additional CAP exposure and induces genomic alterations involved in cell envelope integrity, defence mechanisms and DNA replication, recombination, and repair. Importantly, CAP treatment enhances bacterial susceptibility to the topical antibiotic for wound care mupirocin. These findings provide novel insights into the mechanisms underlying CAP-mediated biofilm control and offer a promising strategy to potentiate existing antimicrobial therapies. (10.1093/femsmc/xtag039)
  DOI : 10.1093/femsmc/xtag039
• Electron temperatures in the ionosphere of Venus from Solar Orbiter/Radio and Plasma Waves instrument
  
  • Vecchio A.
  • Maksimovic M.
  • Galand M. I. F.
  • Bonnin X.
  • Astier P.-L.
  • Edberg N. J. T.
  • Píša D.
  • Boldú J. J.
  • Matteini L.
  • Chust T.
  • Hadid L. Z.
  • Kretzschmar Matthieu
  • Khotyaintsev Yu. V.
  • Souček J.
  • Horbury T.
  • Bale S. D.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2026, 709. Context. On February 18, 2025, Solar Orbiter (SO) completed its fourth gravity assist maneuver of Venus (VGAM4) and reached an unprecedented proximity coming within 378 km of the planet. This flyby was necessary to steer the spacecraft into an orbit outside the plane of the ecliptic. Near the closest approach, only the Radio and Plasma Wave (RPW) and Magnetometer (MAG) instruments were operational; this enabled high-cadence measurements to be taken to investigate the plasma properties of the Venusian ionosphere. Aims. The main goal of this study is to derive the electron density and temperature in the ionosphere of Venus using electric potential measurements from RPW, and to characterize them. Methods. During approximately five minutes around the closest approach, the High Frequency Receiver of RPW detected radio emissions of a type naturally generated by planetary ionospheres whose frequency can be related to the electron density. Using quasithermal noise spectroscopy, we inferred the electron temperature at discrete altitudes and solar zenith angles. Results. Solar Orbiter measured an average density and electron temperature in the ionosphere of Venus of 12 385 ± 148 cm⁻³ and 0.43 ± 0.05 eV, respectively. These values are in agreement with in-situ measurements by Pioneer Venus Orbiter (PVO) obtained at the solar maximum. Binned magnetic fields and temperatures are anticorrelated, which suggests that the magnetic flux ropes, observed in the Venus ionosphere, are more likely non-force-free structures. Conclusions. The findings presented in this paper, together with the measurement from the Parker Solar Probe (PSP) during the third gravity assist, support the conclusion that the plasma density in the Venusian ionosphere above 350 km varies with solar activity, whereas the electron temperature shows a much weaker dependence. Notably, the electron temperature remains consistent across the three missions (SO, PSP, and PVO), despite varying levels of solar activity. This suggests that, over the altitude and solar zenith regions probed, the thermal structure of the Venusian ionosphere is not driven by solar extreme ultraviolet (EUV) heating alone, but is also shaped by external heat sources near the ionopause. Processes such as the damping of whistler mode waves, solar wind ion heating, and thermal conduction from the hot ionosheath appear to play a major role. (10.1051/0004-6361/202557868)
  DOI : 10.1051/0004-6361/202557868
• Climatology of Plasma Irregularities Using ROTI Index From 2008 to 2023 in East West Asia
  
  • Drabindra Pandit
  • Rolland Fleury
  • Christine Amory‐mazaudier
  Space Weather: The International Journal of Research and Applications, American Geophysical Union (AGU), 2026, 24 (4), pp.e2025SW004759. This study investigates characteristics of ionospheric irregularities over the East–West Asian equatorial region using the Rate of TEC Index (ROTI) derived from Global Navigation Satellite System (GNSS) measurements. Data from four stations (GUAM, PIMO, CUSV, and IISC) were analyzed for 2008–2023, covering solar cycle (SC) 24 and the ascending phase of SC 25. While our findings are generally aligned with previous research, this work presents new insights into the complex behavior of ionospheric scintillation in this sector. A key finding is the significant spatial variability in irregularity occurrence, with stations at similar magnetic dip (11–13°) exhibiting varying activity levels. Notable longitudinal asymmetries were also identified, particularly at GUAM, which shows reduced autumnal activity, likely due to local differences in Pre‐Reversal Enhancement (PRE) and magnetic declination. Our study shows a clear daily pattern: scintillation begins after sunset (18:00–19:00 LT), peaks in the late evening (20:00–21:30 LT), and declines by early morning. A slight increase in ROTI is consistently observed just before sunrise at all locations. Temporally, results show dependence on the 11‐year SC and a distinct seasonal pattern, with activity concentrated in equinoctial months. The spring maximum is generally stronger than the autumn one across stations. Finally, although the long‐term trend follows the SC, the relationship is non‐linear. Outliers, such as anomalous activity in 2019, demonstrate that while the Sunspot Number (SSN) is a primary long‐term driver, scintillation is also modulated by short‐term geophysical phenomena. (10.1029/2025SW004759)
  DOI : 10.1029/2025SW004759
• Mercury’s Low‐Latitude Boundary Layer: Identification of Distinct Proton Populations Using MESSENGER Spacecraft Data
  
  • Wang X.
  • Hadid L. Z.
  • Aizawa S.
  • Sahraoui F.
  • Raines J M
  • Lavraud B.
  Journal of Geophysical Research. Planets, Wiley-Blackwell, 2026, 131 (5), pp.e2025JE009617. We have performed a comprehensive analysis of Mercury's Low-Latitude Boundary Layer (LLBL) using data from the MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft during its orbital phase. Using combined magnetic field and ion measurements, we identified 202 LLBL events and categorized them into three distinct types based on proton energy distributions: single-population, double-population, and energy-shifted LLBLs. While the first two types have been observed at Earth, the third is reported here for the first time in a planetary magnetosphere. Each type exhibits unique ion characteristics and distinct local time distribution: (a) single-population LLBLs show magnetosheath-like energy spectra; (b) double-population LLBLs contain two coexisting components with energy similar to that of the magnetosheath and magnetosphere; and (c) energy-shifted LLBLs exhibit a smooth energy increase from the magnetosheath level to the magnetospheric level. These types are clearly separated in local time, with singlepopulation LLBLs near the subsolar region, double-population LLBLs extending to dusk, and energy-shifted LLBLs on the dawnside, reflecting distinct plasma transport and energization processes. Energy-shifted LLBLs exhibit significant perpendicular energization in the dawn region, where magnetosheath ions entering the magnetosphere drift dawnward and are further energized by cross-field potential drops. Mercury's smaller geometric radius and magnetic field curvature, which lead to stronger ion drift, likely make this drift-driven energization more pronounced than at Earth. These results offer new insight into plasma transport across Mercury's magnetopause and lay the foundation for future BepiColombo investigations, which will provide higher temporal and energy resolution multi-point observations of Mercury's magnetospheric dynamics.</p><p>Plain Language Summary Mercury, the smallest and closest planet to the Sun in our Solar System, has a magnetic field that interacts with the solar wind, a fast stream of charged particles from the Sun. At this interaction region, a boundary layer forms that affects how solar wind particles enter the magnetosphere. Understanding the formation of this boundary helps us learn how Mercury's space environment works and how it differs from Earth's. Using observations from NASA's MESSENGER spacecraft, we examined more than 200 events in this boundary region at low latitudes. We found that the energy distribution of particles falls into three categories, each showing different energy patterns and occurring at different local times around the planet. One category, where particle energies gradually increase as they move inward, has never been reported at any planet before. These findings offer new clues to how particles and energy are transported in Mercury's magnetic environment and will help interpret upcoming measurements from the BepiColombo mission (10.1029/2025je009617)
  DOI : 10.1029/2025je009617
• Determination of the accuracy of actinometry and line ratio techniques in an O2 glow discharge: I. Comparison of absolute oxygen atom densities with CRDS measurements
  
  • Baratte Edmond
  • Kuijpers Lex
  • Silva Tiago
  • Guerra Vasco
  • van de Sanden M C M
  • Booth Jean-Paul J-P
  • Guaitella Olivier
  Plasma Sources Science and Technology, IOP Publishing, 2026, 35 (1), pp.015009. The accuracy of oxygen atom density measurements in plasmas by optical emission actinometry was tested by comparison to simultaneous direct absorption measurements on the 1 D 2 -&gt; 3 P 2 transition by cavity ringdown spectroscopy (CRDS). The accuracy of the latter technique depends only on the accuracy to which the transition probability is known. Measurements were performed on a glow discharge in O 2 operating between 0.5 and 5 Torr, and using both Ar and Xe as the actinometer gas. The rate constants for electron impact excitation, and thus the actinometry calibration factors, were calculated from the (measured) reduced electric field using a Boltzmann equation solver (Loki-B). Several sets of cross-section were tested for the EEDF calculation and for the electron impact excitation to the specific levels of O, Ar and Xe used for actinometry. The best results were obtained with the IST Lisbon cross-section set for O 2 and O, and the BSR500 excitation cross-sections for Ar and Xe. Good agreement with the CRDS trends and absolute values was observed when using Xe as the actinometer gas, whereas with Ar the trends were well reproduced but it was necessary to increase the electron impact cross-section of the transition Ar( 1 S 0-&gt; 2p 1 ) of the BSR500 database by a factor of 3˘0.3 to reproduce the absolute values. (10.1088/1361-6595/ae24a9)
  DOI : 10.1088/1361-6595/ae24a9
• Towards Gravitational Wave Turbulence within the Hadad-Zakharov metric
  
  • Gay Benoît
  • Babichev Eugeny
  • Galtier Sébastien
  • Noui Karim
  Physical Review D, American Physical Society, 2026, 113 (12), pp.124074. The theory of gravitational wave turbulence describes the long-term statistical behaviour of a set of weakly nonlinear interacting waves. In this paper, we aim to study aspects of gravitational turbulence within the framework of general relativity using the Hadad-Zakharov (HZ) metric. The latter is parameterised by four functions (the coefficients of a diagonal metric) that must satisfy seven non-trivial Einstein equations, six of which are independent. The issue of their mutual compatibility is therefore essential, yet it has so far been overlooked. In this work, we argue that these equations can be compatible in the weakly nonlinear regime under specific conditions. Our analytical investigation is complemented by direct numerical simulations performed with a new GPU-based code, TIGER. A comparative analysis of the evolution of the Ricci and Kretschmann scalars indicates that gravitational wave turbulence corresponds to the propagation of a genuine physical degree of freedom. These numerical findings, however, must be interpreted with caution, given the difficulty of satisfying all seven Einstein equations simultaneously with sufficient accuracy. On the other hand, our simulations reproduce well the expected properties of the wave turbulence regime, with the emergence of a dual cascade of energy and wave action, and for the latter the observation of the Kolmogorov-Zakharov spectrum. In addition, our analysis reveals that the canonical variables of the problem evolve towards a nearly Gaussian statistical distribution punctuated by intermittent coherent (spatially localised and long-living) structures. In contrast to the canonical variables, the structure functions of the gauge-invariant metric components exhibit monofractal behaviour, which is a classical property of wave turbulence. (10.1103/vc5p-c3w8)
  DOI : 10.1103/vc5p-c3w8
• Plasma plume symmetrization by electron rotation and ion detachment properties in a diverging magnetic nozzle
  
  • Pioch Romain
  • Chabert Pascal
  • Désangles Victor
  Physical Review E, American Physical Society (APS), 2026, 113 (3), pp.035209. The ion flux direction in a rapidly diverging magnetic field and the role of Earth's magnetic field in plasma dynamics are investigated experimentally using a low power electron cyclotron resonance thruster. The comparison between ion trajectories measured with a directional Faraday cup and the magnetic field geometry allows us to assess some of the ion flow properties. The results show that the ion trajectories follow the magnetic field lines in the center part of the plasma plume but not on its edges, defining the detachment location. Once detached, ions follow straight line trajectories, and their detachment has a divergent nature. The effect of the thruster operating condition on these properties is explored. Plasma potential measurements carried out with an emissive probe reveal the presence of a large radial electric field, pointing outward at the detachment point, that explains the divergent nature of the ion detachment. The amplitude of the induced E × B drift rotation of the electrons in the nozzle damps the disymmetrizing influence of Earth's magnetic field on the electron dynamics and leads to an axisymmetric plasma plume. This mechanism is demonstrated using single particle simulations. (10.1103/3twz-bcvk)
  DOI : 10.1103/3twz-bcvk
• Laser induced fluorescence of singly ionized atomic iodine: Measurements in the plasma source of an electric propulsion device
  
  • Pioch Romain
  • Sagnimorte Marie-Alix
  • Esteves Benjamin
  • Drag Cyril
  Physical Review E, American Physical Society (APS), 2026, 114 (3), pp.035201. A laser induced fluorescence (LIF) scheme is investigated to probe singly ionized iodine ions (I⁺) in electric propulsion devices. The transition 6s⁵S$_2^o$ → 6p⁵P₃ at 516.261 nm is considered and the theoretical computation of the weights and positions of the hyperfine structure is carried out. First, the measurement of the fluorescence signal is performed in the ionization chamber of an rf gridded ion engine, the PEGASES thruster, demonstrating that the chosen LIF scheme is well suited for the study of electric propulsion devices operating with iodine. Second, spatial measurements of the temperature, velocity, and density are taken in this plasma source for several conditions of iodine pressure from 0.5 to 10 mTorr. First, an increase of the temperature of the ionic excited population close to the antenna is observed. Second, the analysis of the Doppler shift of the LIF profile shows the acceleration of the ions in the source. Third, the comparison of the measured LIF profiles with previous measurements shows that the density of the probed lower excited state is proportional to that of the ground state in the conditions of the experiment. (10.1103/jmh3-hwd8)
  DOI : 10.1103/jmh3-hwd8
• Equatorial ionospheric plasma bubbles during intense geomagnetic storms of Solar Cycle 25
  
  • Imtiaz Nadia
  • Calabia Andres
  • Anoruo Chukwuma
  • Zahid Aqsa
  • Amory-Mazaudier Christine
  • Adhikari Binod
  Annales Geophysicae, European Geosciences Union, 2026, 44 (1), pp.489-509. This study examines the low-latitude ionospheric response to four intense geomagnetic storms during Solar Cycle 25 (March, April, November 2023, and May 2024), focusing on Equatorial Ionization Anomaly (EIA) variations and post-sunset plasma irregularities. We used the Weimer (2005) model for Joule Heating (JH), Madrigal total electron content (TEC) maps, and GNSS-derived ROTI to analyze storm-time changes in EIA structure and equatorial plasma bubbles (EPBs). The May 2024 storm exhibited the strongest post-sunset JH, particularly near the June solstice, while March and April storms showed moderate JH and November the lowest. Equinox storms produced nearly symmetric JH patterns, while solstice storms revealed interhemispheric asymmetries. Following JH thresholds are used for the classification of storms: weak (20–30 mW m−2, November), moderate (30–50 mW m−2, March/April) and strong (&gt;50 mW m−2, May). JH, together with storm-time electric fields and equatorial meridional winds, influence the location, strength, hemispheric asymmetry, and the generation or suppression of plasma irregularities of the EIA crest. The generation of ionospheric plasma irregularities and their geographical distribution strongly depend on EIA's density gradients and general structure. Well-developed double-crest EIAs with steep density gradients favor post-sunset irregularities, while single-crest or merged EIAs are less favorable. Fluctuations in the IMF Bz drive east-west prompt penetration electric fields that dynamically modulate the F region, altering the plasma fountain effect, the EIA structure, and the distribution of plasma bubbles after sunset. These results suggest that during geomagnetic storms, the combined effects of storm-driven electrodynamics and neutral winds modulate low-latitude ionospheric variability, influencing EIA dynamics and the formation of plasma irregularities. (10.5194/angeo-44-489-2026)
  DOI : 10.5194/angeo-44-489-2026
• Dynamics of switchback-like magnetic deflection induced by a propagating coronal jet
  
  • Touresse J.
  • Pariat E.
  • Froment C.
  • Wyper P.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2026, 714 (A282). The Parker Solar Probe (PSP) mission revealed the ubiquity of switchbacks (SBs), sharp and localised magnetic deflections, in the nascent solar wind. This finding has sparked significant interest in their origin and formation mechanisms. Among the proposed scenarios, a solar origin associated with solar jets has emerged. Solar jets are collimated, impulsive, and sharp-edged features associated with magnetic reconnection and they generate an Alfvénic torsional wavefront propagating into the heliosphere. In this study, we investigate whether a realistic spacecraft sampling of a propagating solar jet can produce synthetic in situ signatures consistent with PSP-observed SBs. We also characterise the three-dimensional (3D) magnetic topology of the underlying structure and assess how the magnitude of the magnetic deflection evolves with the surrounding environment. We performed a 3D magnetohydrodynamic simulation of a solar jet propagating into the ambient solar wind. A virtual spacecraft trajectory, constructed from the actual PSP orbit during its 22 nd perihelion, was embedded within the simulation to generate synthetic in situ measurements. The simulation reproduces SB-like magnetic signatures with durations and profiles consistent with PSP observations, confirming earlier results obtained using simplified trajectories. For the first time, we directly visualised the fully 3D magnetic topology of a jet-driven SB region. Two distinct families of magnetic field lines are identified: one exhibiting a single magnetic deflection, and another showing two sequential deflections propagating along the same field line. In both configurations, the deflections act as outward-propagating Alfvénic structures. The magnitude of the magnetic deflection is strongly modulated by the background plasma β, with significant amplification in low-β regions and a more moderate evolution where β ∼ 1. These results demonstrate that propagating solar jets can naturally produce Alfvénic, SB-like structures when sampled along realistic in situ trajectories. The magnetic topology of SB regions is inherently 3D and structurally diverse. Their evolution depends on the surrounding plasma β, with complete magnetic reversals requiring longer residence times in low-β environments. This study supports the interpretation that at least a fraction of the SBs observed by PSP may have a solar origin and it provides new constraints for interpreting PSP measurements in terms of their underlying magnetic structure. (10.1051/0004-6361/202659513)
  DOI : 10.1051/0004-6361/202659513
• Oxygen atom density and kinetics in intermediate-pressure radiofrequency capacitively-coupled plasmas in pure O2
  
  • Zhang Shu
  • Volynets Andrey
  • Curley Garrett A
  • Booth Jean-Paul
  Plasma Sources Science and Technology, IOP Publishing, 2026, 35 (6), pp.065010. We have studied radiofrequency (13.56 MHz) capacitively-coupled plasmas in pure O2 at intermediate pressures (67–800 Pa) using single-mode laser cavity ring-down spectroscopy (CRDS) of oxygen atoms at 630 nm. The absolute atom densities and translational temperatures (from Doppler broadening) in continuous plasma were determined over a range of pressures and RF power (50–900 W). At higher pressures (267–800 Pa), the O-atom mole-fraction increases with RF power and decreases with pressure, reaching a maximum of 15%. However, at lower pressures (67–133 Pa) it passes through a distinct maximum with power before decreasing significantly. The atom recombination processes were probed by time-resolved measurements in the afterglow of pulse-modulated plasmas. At 67 and 133 Pa the atom loss is dominated by surface recombination, and we see clear evidence that this rate is increased by energetic ion bombardment. However, this effect only partially explains the observed decrease in dissociation at high RF power. At higher pressures gas phase recombination mechanisms dominate oxygen atom loss, although gas convection driven by gas cooling in the afterglow complicates quantitative analysis of the time-resolved data. Time-resolved CRDS measurements of the continuum absorption adjacent to the O atom resonance allow the O− negative ion density to be determined, as well as indicating the creation of ozone in the afterglow. At 133 Pa, the trends with RF power of the O2 dissociation, O- density and gas temperature suggest a transition to a plasma mode at high power which has fewer electrons at energies capable of dissociating O2. (10.1088/1361-6595/ae7634)
  DOI : 10.1088/1361-6595/ae7634
• Anisotropic truncation for turbulent transport and zonal flows in the Hasegawa–Wakatani system
  
  • Guillon P
  • Angles R
  • Sarazin Yanick
  • Gürcan Ö
  Plasma Physics and Controlled Fusion, IOP Publishing, 2026, 68 (8), pp.085022. Reduced models based on an anisotropic truncation of the Fourier space, retaining only a few poloidal wave-numbers while keeping the full radial resolution, are developed and first applied to the Hasegawa–Wakatani system. The impact of the truncation is studied first by considering the fixed-gradient formulation, and by comparing to direct numerical simulations (DNSs). The turbulent particle flux, and the transition from quasi-two dimensional turbulence to the zonal flow (ZF) dominated state, are used as the main criteria for validation. It is found that at least 4 poloidal modes, distributed around the most unstable mode, are needed to observe a sharp transition, and that about 10 modes are needed to reproduce each transport regime. Then, similar reduced models are developed in a flux-driven formulation and compared to the DNS, focusing on two cases far from the nonlinear threshold of the transition from turbulence to zonal dominated states of the fixed gradient formulation. In that case, using 10 modes allows to match the probability distribution function of the particle flux of the DNS approximately. Considering the role played by different poloidal scales in the turbulent cascade, it is observed that in the turbulent state, an inverse energy cascade in radial wave-numbers takes place at large poloidal scales, while a forward enstrophy cascade in radial wave-numbers is observed to occur at smaller poloidal scales. Moreover, when they form, ZFs feed on poloidal scales that are around and slightly smaller than the injection scale, while giving their energy to the larger poloidal scales. In that case, there is an anisotropic inverse energy transfer, akin to inverse cascade, from the energy injection to the large poloidal scales through ZFs, while the forward enstrophy cascade seems to stay isotropic. (10.1088/1361-6587/ae92b2)
  DOI : 10.1088/1361-6587/ae92b2
• Response of Ionospheric Parameters at Low‐Latitude and Mid‐Latitude Stations to Geomagnetic Storms of March and April 2025
  
  • Ojo Olakunle L
  • Amory‐mazaudier C
  • Abe Oladipo Emmanuel
  • Kashcheyev A
  • Nava B
  • Olumodimu Olugbenga
  • Canning R
  • Ajiboye Yinka
  • da Silva M V
  • Nel A
  • Giday M N
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2026, 131 (8), pp.e2026JA035402. This study investigates ionospheric responses to geomagnetic storms of 21-24 March and 15-17 April 2025 using GNSS-derived total electron content (TEC), magnetometer observations, and thermospheric O/N 2 measurements at low and mid-latitudes across the Northern Hemisphere of the Europe-Africa sector. The March storm reached a SYM-H minimum of -72 nT, driven by a CME with a brief southward IMF-Bz interval followed by a high-speed stream (HSS). Low-latitude African stations recorded night-time TEC enhancements of +85% to +168%, attributed to prompt penetration electric fields (PPEFs) driving night-time upward E × B plasma transport, while mid-latitude European stations exhibited mixed deviations. Elevated daytime O/N 2 ratios indicate reduced molecular recombination in the F region during the daytime, consistent with positive daytime ionospheric responses at low latitudes. The April storm reached a SYM-H minimum of -150 nT, from a compound CME-HSS interaction sustaining southward IMF-Bz conditions. During 16-17 April, mid-latitude European stations experienced TEC reductions of -52% to -69% in the main phase, while low-latitude stations displayed alternating responses. O/N 2 ratios decreased to 0.6-0.8 across the sector, consistent with enhanced molecular recombination and negative ionospheric responses at mid-latitudes. Magnetometer observations revealed storm-time perturbations after sudden commencement, consistent with prompt penetration electric fields, followed by latitudinal disturbances during late main and recovery phases. Magnetic signatures for disturbed ionospheric currents Diono, negative at low latitudes and positive at mid-latitudes, agree with the polarity predicted by the disturbance dynamo model of Blanc and Richmond (1980, https://doi.org/10.1029/ja 085ia04p01669). These results demonstrate how storm evolution and solar-wind forcing shape ionospheric variability within the Europe-Africa sector. (10.1029/2026ja035402)
  DOI : 10.1029/2026ja035402
• Mutual impedance experiments in a laboratory plasma: Experimental validation of numerical modeling
  
  • Dazzi P.
  • Henri P.
  • Bucciantini L.
  • Briaud E.
  • Brochot J. Y.
  • de Keyser J.
  • Edberg N. J. T.
  • Issautier K.
  • Kretzschmar Matthieu
  • Lecas T.
  • Revillet C.
  • Souffi H.
  • Vengeons G.
  • Wattieaux G.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2026, 707. Context. In situ measurements of space plasma are necessary to explore heliospheric and planetary ionized environments. Mutual impedance experiments are an active plasma diagnostic technique used to measure the properties of space plasmas, including the plasma density and the electron temperature. Although various models have been developed for unmagnetized space plasmas, they fail to describe the instrument behavior in magnetized plasmas, such as the ionosphere and magnetosphere of magnetized planets and moons. A quantitative instrument model of the mutual impedance experiment is required, however, for current and future space missions, including ESA/JAXA BepiColombo and ESA JUICE, which will both conduct mutual impedance experiments (PWI/AM2P and RPWI/MIME, respectively). Aims. We develop an instrument model for exploring and quantitatively characterizing mutual impedance experiment measurements performed in planetary plasmas, with the goal of providing in situ diagnostics of the plasma density and electron temperature. Methods. To reach this goal, we combined numerical investigation and laboratory experiments. We investigated the experimental regime of high magnetization for the first time, where the electron gyrofrequency is higher than the plasma frequency, both experimentally and numerically. On the experimental side, we built a setup composed of a plasma chamber, a mutual impedance experiment, and a Langmuir probe. With this, we achieved a controlled plasma environment representative of magnetized space plasmas, which we diagnosed with two independent plasma instruments. On the numerical side, we developed a model for magnetized mutual impedance experiments that took the geometry of the mutual impedance antennas and the plasma chamber into account and that employed a kinetic linear description of the plasma electrons. Results. First, we characterized the plasma environment generated in the plasma chamber: the achievable plasma parameters, the stability, and the repeatability of the plasma conditions. Second, we validated the instrument model by comparing the numerical model predictions to the measurements obtained in the plasma chamber. Third, we extracted the plasma density and temperature from in situ mutual impedance measurements using our new numerical instrument model, and we validated them using the independent in situ measurements from the Langmuir probe. Conclusions. This work (i) proves that mutual impedance experiments are able to provide robust plasma diagnostics in a magnetized space plasma environment, and (ii) develops a methodological framework that will be used for the planetary space missions BepiColombo and JUICE to perform both the in-flight calibration and the exploitation of the measurements from PWI/AM2P and RPWI/MIME, respectively, in the magnetospheres of Mercury, Jupiter, and Ganymede. (10.1051/0004-6361/202554409)
  DOI : 10.1051/0004-6361/202554409