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Journal articleKretzschmar M, Vecchio A, Krasnoselskikh V, et al., 2026,
First in Situ Detection of the Magnetic Component of a Solar Type III Radio Wave
, Astrophysical Journal Letters, Vol: 1001, ISSN: 2041-8205Solar radio bursts, and astrophysical radio emissions in general, are observed either in space or on the ground by measuring their fluctuating electric field. Here, we report the first measurement of the magnetic component of a solar radio wave, observed simultaneously by the Solar Orbiter and Parker Solar Probe missions. The observations were made during the type III radio burst on 2021 October 28. The analysis of the wave polarization and magnetic and electric field amplitudes allows us to estimate the refractive index and put constraints on the direction of the wave. The wave is found to be consistent with an ordinary-mode wave and with a source near the southeast limb of the Sun. These results pave the way for future observations and analyses of the magnetic field of radio waves, in particular, for solar radio bursts.
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Journal articleMöstl C, Davies EE, Weiler E, et al., 2026,
On the Magnetic Field Evolution of Interplanetary Coronal Mass Ejections from 0.07 to 5.4 au
, Astrophysical Journal, Vol: 1001, ISSN: 0004-637XA central question for understanding interplanetary coronal mass ejection (ICME) physics and improving space weather forecasting is how ICMEs evolve in interplanetary space. We have updated one of the most comprehensive in situ ICME catalogs to date, which now includes 1976 events from 11 space missions covering over 34 yr, from 1990 December to 2025 August. We have combined existing catalogs including magnetic obstacles (MOs) and identified and added boundaries of an additional 807 (40.8%) events. With this catalog, we demonstrate the most extensive analysis to date of total ICME magnetic field values as a function of heliocentric distance. Parker Solar Probe has observed six ICMEs at <0.23 au (until 2025 April), and Solar Orbiter and BepiColombo have added more events near 0.3 au, bridging the major observational gap towards the solar corona. Our main result is that a single power law can describe the evolution of the mean total magnetic field (exponent value of k = −1.57) and maximum field (k = −1.53) for ICMEs with MOs, from 0.07 to 5.4 au. Extending the power law to the solar photosphere reveals a strong inconsistency with magnetic field magnitudes observed in the quiet Sun and active regions by 2 and 4 orders of magnitude, respectively. We introduce a multipole-type power law with two exponents, k <inf>1</inf> = −1.57, and k <inf>2</inf> = −6, relating the ICME magnetic field magnitude to an average solar active region field strength. These results present important observational constraints for the evolution of ICMEs from the Sun to the heliosphere.
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Journal articleStrucka J, Sterbentz DM, Lukic B, et al., 2026,
Passive freeze-out of the Richtmyer-Meshkov instability
, Physical Review Letters, Vol: 136, ISSN: 0031-9007<jats:p>The Richtmyer-Meshkov instability (RMI) poses a major challenge in inertial confinement fusion (ICF) due to its role in mixing and performance degradation. We report the first experimental observation of passive freeze-out of RMI in a low-pressure surrogate regime, an instability stagnation effect induced without modifying the driving pressure pulse or the target surface geometry. Using additively manufactured subsurface voids in a sinusoidal target, we convert a single shock into a sequence of weaker shocks that suppress instability growth upstream of the surface by over 70%. High-speed x-ray imaging and hydrodynamic simulations suggest that this suppression arises primarily from temporal shaping, with lesser contributions from spatial curvature and shock weakening. Our results demonstrate a driver-independent pathway for controlling shock-driven hydrodynamic instabilities relevant to ICF and other high energy density systems.</jats:p>
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Journal articleWojciechowska I, Gryspeerdt E, 2026,
Reconstructing albedo from mean cloud properties
, Atmospheric Chemistry and Physics, Vol: 26, Pages: 4571-4582, ISSN: 1680-7316Liquid marine clouds exert a substantial control on the Earth-atmosphere energy system through their large global coverage and high reflectivity of shortwave radiation, resulting in overall negative radiative impact. Previous studies showed that the two dominant factors determining their albedo are cloud fraction (CF) and liquid water path (LWP), but this relationship varies in regions of high aerosol loading. In this work, a simplified kernel was built to assess how well the top of atmosphere (TOA) all-sky albedo (α) can be estimated from the given properties of marine liquid clouds: CF, LWP and cloud droplet number concentration (<inf>Nd</inf>), and to what extent this approach applies globally. The study uses data retrieved from MODIS and CERES instruments for a near-global ocean domain (60° S–60° N) covering the period 2003–2021. The results showed that the albedo is only reconstructed to within 10 % in less than 40 % of cases. Several modifications of investigated method were tested for the improvement in albedo reconstructions. It was found that the number of biases decreases when the maximum solar zenith angle is considered, as well as if the CF–LWP–<inf>Nd</inf>–α kernel is calculated on a higher spatial resolution grid. The findings show that the relationship between the TOA albedo of a scene of clouds and the retrieved mean cloud properties is not universal and while accounting for regional variation is one way to address this, a better understanding of this effect is still needed to reduce uncertainty in aerosol-cloud interactions.
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Journal articleDesai MI, Drake JF, Swisdak M, et al., 2026,
Proton and Heavy Ion Acceleration by Magnetic Reconnection at the Near-Sun Heliospheric Current Sheet
, Astrophysical Journal, Vol: 1000, ISSN: 0004-637XMagnetic reconnection at the near-Sun heliospheric current sheet (HCS) dissipates the Parker spiral and converts magnetic energy into plasma kinetic energy. During Encounter 14 at a radial distance of ∼16.25 R <inf>⊙</inf>, Parker Solar Probe observed an HCS crossing where reconnection-driven acceleration—likely facilitated by merging large-scale flux tubes—energized protons up to ∼400 keV. This energy gain is ≈1000 times greater than the available magnetic energy per particle. We present here a comprehensive analysis of pitch-angle distributions and differential energy spectra for protons and heavy ions (He, O, and Fe) in conjunction with local wave activity during this crossing. Our results provide the first direct in situ observations of simultaneous proton and heavy-ion energization during HCS reconnection. Crucially, we find that heavy-ion power-law spectral indices differ significantly from those of protons, contradicting previous simulations that predict species-independent slopes. We further demonstrate that ion beams and anisotropies produced during reconnection drive waves in the ion cyclotron range of frequencies. Finally, we show that proton pitch-angle scattering is stronger than that of heavy ions, which may account for the flatter spectra or harder spectral indices observed in the heavy-ion populations. These observations provide definitive evidence for in situ reconnection-driven acceleration at the near-Sun HCS and necessitate the inclusion of species-dependent transport and acceleration efficiencies in contemporary reconnection-based particle energization models.
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Journal articleKim K, Modolo R, Edberg NJT, et al., 2026,
Plasma Dynamics and Structure of Titan's Induced Magnetosphere From Wave, Magnetic Field, and Plasma Measurements
, Journal of Geophysical Research Space Physics, Vol: 131, ISSN: 2169-9380In this study, we combine Cassini fields and particle observations to investigate Titan's induced magnetosphere from the TA to T82 flybys, including flybys from the Cassini prime, equinox, and part of the solstice mission, to investigate the average location and the shape of Titan's induced magnetosphere. Although earlier studies have provided valuable information on Titan's induced magnetosphere, they were largely based on separate analyses of fields and particle data. We provide an integrated map of electron density and temperature in Titan's near plasma environment to outline the external boundary of the induced magnetosphere. We identify a dense ionospheric region and an extended plasma wake with electron densities ranging between (Formula presented.) and (Formula presented.) c (Formula presented.). In addition, we systematize the spatial distribution of pick-up ions at Titan with respect to the background convective electric field. We indicate that pickup ions are found in the positive hemisphere of the Kronian plasma convective electric field. The mass of the observed pickup corresponds to methane group ions, (Formula presented.) ions as well as protons and molecular hydrogen ions. The Kronian background electric field progressively accelerates these ions, and we estimate its intensity by reconstructing the radial energy gain of this population in response to the convective electric field. We find the estimated from the pickup ions electric field values within 0.05 mV (Formula presented.) and 1.92 mV (Formula presented.) range, which is consistent with an estimate of 0.61 mV (Formula presented.) deduced from (Formula presented.) computation.
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Journal articleOka M, Russell AJB, Harada Y, et al., 2026,
Universality of the Scaling Law for Particle Energization in Collisionless Plasmas
, Astrophysical Journal, Vol: 1000, ISSN: 0004-637XParticles are energized—heated and accelerated to nonthermal energies—in laboratory, space, solar, and astrophysical plasmas. In collisionless plasmas, ion and electron temperatures are often unequal and cannot be fully understood within the framework of magnetohydrodynamics (MHD). In this context, a relation, Δϵ<inf>s</inf> = q<inf>s</inf>VBL<inf>s</inf>, for each species can be useful, where Δϵ<inf>s</inf> is the energy gain for species s, measured in the plasma rest frame, relative to the upstream region of shocks and magnetic reconnection; q<inf>s</inf> is the charge; V is the plasma bulk flow speed; B is the magnetic field strength; and L<inf>s</inf> is a characteristic length scale of energization. From this relation, we recently derived semiempirical scalings for ion and electron temperature increases across shocks and magnetic reconnection in Earth’s plasma environment. However, it remains unclear how broadly these scalings apply. Here we show that the same scalings explain temperature increases in other plasma environments such as laboratory experiments, planetary magnetospheres, solar flares, and supernova remnant shocks. Combined with another recent report that the maximum energy of particles in various plasma environments follows the same relation when L<inf>s</inf> is taken as the system size, our results indicate that Δϵ<inf>s</inf> = q<inf>s</inf>VBL<inf>s</inf> provides a novel framework that universally captures particle energization—both heating and acceleration to nonthermal energies. Additionally, the scaling captures the essential MHD trends while revealing systematic deviations that point to kinetic effects beyond fluid models, highlighting promising directions for theoretical and simulation studies.
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Journal articleKim TK, Reisenfeld DB, Wilson RJ, et al., 2026,
Comprehensive characterization of water group ion composition and distributions in Saturn's magnetosphere with Cassini plasma spectrometer data
, Journal of Geophysical Research (JGR): Space Physics, Vol: 131, ISSN: 2169-9380Saturn's magnetosphere is continuously supplied with neutrals from the Enceladus plume and the icy rings, which undergo ionization and charge-exchange to form a complex water-group plasma environment. While the Cassini Plasma Spectrometer (CAPS) instrument has provided extensive compositional information, detailed separation of individual water-group ion species in time-of-flight (TOF) data has not previously been achieved. In this study, we perform forward modeling of CAPS-IMS energy-per-charge (E/Q) and TOF spectra obtained between 2004 and 2012 to resolve O+, OH+, H2O+, and H3O+ and to characterize their plasma properties, including number density, temperature, and thermodynamic κ. Our results demonstrate that O+ is the dominant thermal ion species throughout Saturn's magnetosphere, comprising up to ∼70% of the total ion population beyond ∼5 Saturn radii (RS). In contrast, molecular ions such as OH+, H2O+, and H3O+ dominate closer to Enceladus but rapidly dissociate into atomic ions between ∼5 and 10 RS. This radial region is also characterized by the steepest increase in plasma flow speed, which rises from ∼40% to ∼80% of rigid corotation. Simultaneously, ion velocity distributions approach Maxwell–Boltzmann equilibrium, as indicated by high kappa values. These findings provide new constraints on the ion–neutral chemistry that regulates the balance between molecular and atomic ions in Saturn's magnetosphere. They also emphasize the critical role of the 5–10 RS region as a transition zone for both plasma composition and dynamics. Our results refine previous CAPS-based studies and underscore the need to incorporate seasonal variability and ionospheric coupling into future global models of Saturn's plasma environment.
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Journal articleRecchiuti D, Franci L, Matteini L, et al., 2026,
Evolution of ion distribution functions in ionospheric plasmas perturbed by Alfvén waves
, Journal of Plasma Physics, Vol: 92, ISSN: 0022-3778This study investigates ion kinetic effects during the parametric decay instability (PDI) of parallel-propagating Alfvén waves under plasma conditions characteristic of the Earth’s ionosphere. By using a series of hybrid particle-in-cell simulations, we examine the evolution of ion velocity distribution functions (VDFs) in ultra-low-beta plasmas. Our numerical campaign systematically explores the dependence on key parameters (plasma beta, pump-wave amplitude and polarisation, and ion composition). To emphasise the role of kinetic effects, we choose to trigger the PDI with a dispersive mother wave with wavelength comparable to the ion characteristic inertial length. Our results reveal pronounced non-thermal VDF modifications, including parallel heating and the formation of secondary ion beams, linked to the nonlinear evolution of parametric decay instability. By varying the plasma beta and the pump-wave amplitude, we identify a critical regime where rapid and complete broadening of the velocity distribution function is observed, triggering bidirectional ion acceleration. Notably, simulations modelling realistic ionospheric conditions demonstrate that even low-amplitude Alfvénic perturbations can induce significant VDF spreading and ion beam generation, with hydrogen ions exhibiting stronger effects than oxygen. These non-thermal microscopic processes offer a plausible mechanism for particle precipitation in space weather events. This work represents the first comprehensive study with hybrid simulations of PDI-driven ion kinetics in ultra-low-beta plasmas, providing quantitative estimates for the time delay between electromagnetic wave impact and ion VDF modification, and new insights into wave–particle interactions that may contribute to ion acceleration, precipitation processes and space plasma dynamics.
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Journal articleLopez-Marti F, Czaja A, Messori G, et al., 2026,
Modulation of North Atlantic atmospheric rivers by the Gulf Stream
, Quarterly Journal of the Royal Meteorological Society, Vol: 152, ISSN: 0035-9009Extreme precipitation and wind events in Western Europe are often driven by atmospheric rivers (ARs) developing over the North Atlantic Ocean. Even though research has explored AR variability in relation to large-scale atmospheric dynamics and the North Atlantic Storm Track, gaps remain in understanding how oceanic variability influences AR activity, particularly within the eddy-rich environment of the Gulf Stream extension. The enhanced ocean heat transport and mesoscale eddy activity associated with this western boundary current can influence large-scale dynamics, modulate moisture availability in the lower atmosphere, and potentially control the AR activity downstream. In this study, we evaluated ocean mesoscale features, oceanic heat supply, and surface heat fluxes in the Gulf Stream extension region at monthly time-scales. We assessed their downstream impact on AR activity using state-of-the-art observational datasets. Our analysis identified winter and spring as the key seasons for interactions between Gulf Stream conditions and ARs. Higher ocean heat transport and mesoscale sea-surface height (SSH) meandering were associated with a northward shift in downstream AR activity and a positive North Atlantic Oscillation (NAO) pattern, although the atmospheric response is weaker in the latter case. In contrast, stronger than average surface heat fluxes in the Gulf Stream were linked to a southward shift of ARs and a strong negative NAO pattern, suggesting a dominant atmospheric influence that enhanced moisture availability and modulated North Atlantic dynamics. These results show that the Gulf Stream plays an important role in controlling the latitudinal variability of ARs over the Euro-Atlantic sector during winter and spring.
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Journal articleWang S, Yang P, Brindley HE, et al., 2026,
Enhanced Full Spectral Temperature-Dependent Refractive Index of Liquid Water From Supercooled to Ambient Conditions
, Geophysical Research Letters, Vol: 53, ISSN: 0094-8276A new compilation of the complex refractive index of liquid water is presented, spanning temperatures from (Formula presented.) (near homogeneous freezing) to (Formula presented.) K and wavelengths from (Formula presented.) μm to 10 m. The real part of the refractive index is derived using the Kramers–Kronig relation, where the imaginary part is constrained by measurements reported in literature and validated through the f-sum rule. The result reveals a significant temperature dependence, especially at wavelengths beyond the near-infrared. Sensitivity analyses in the infrared split-window and microwave spectral regime demonstrate substantial differences in bulk optical properties between supercooled and ambient conditions. These findings manifest the importance of accounting for temperature-dependent refractive indices in optical radiative transfer and simulations.
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Journal articleCeppi P, Wilson Kemsley S, Andersen H, et al., 2026,
Emerging low-cloud feedback and adjustment in global satellite observations
, Atmospheric Chemistry and Physics (ACP), Vol: 26, Pages: 4153-4171, ISSN: 1680-7316From mid-2003 to mid-2024, a global decrease in low-cloud amount enhanced the absorption ofsolar radiation by 0.22±0.07Wm−2 per decade (±1σ range), accelerating the energy imbalance trend duringthat period (0.44Wm−2 per decade). Through controlling factor analysis, here we show that the low-cloudtrend is due to a combination of cloud feedback and adjustments to greenhouse gases and aerosols (respectively 0.09±0.02, 0.05±0.03, and 0.03±0.03Wm−2 per decade), which jointly account for 74% of the trend. The contribution of natural climate variability is weak but uncertain (0.01±0.08Wm−2 per decade), owing to apoorly constrained trend in boundary-layer inversion strength. Importantly, the observed low-cloud radiativetrend lies well within the range of values simulated by contemporary global climate models under conditionsclose to present day. Any systematic model error in the representation of present-day global energy imbalancetrends is thus likely to originate in processes unrelated to low clouds.
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Journal articleNair V, Gryspeerdt E, Arola A, et al., 2026,
Observing the role of wind-driven processes in the evolution of warm marine cloud properties
, Atmospheric Chemistry and Physics, Vol: 26, Pages: 4049-4066, ISSN: 1680-7316The cloud droplet effective radius is a key variable when evaluating the interactions between aerosols and clouds. The activation of fine-sized sea salt from the ocean results in the formation of more but smaller cloud droplets (reducing the effective radius) in marine stratocumulus. Coarse sea spray aerosols are generated for high surface wind speeds and act as giant cloud condensation nuclei, which activate to form larger droplets. This increases the effective radius and initiates precipitation. These high wind speeds also lead to enhanced moisture fluxes from the ocean surface. Although the opposing impacts of wind-driven fine and coarse marine sea spray aerosols have been documented, their observations have been limited to instantaneous satellite images. In this work, a novel framework is introduced that uses short-timescale observations of the temporal evolution of clouds to identify, isolate, and extract the process fingerprints of marine sea-salt and surface fluxes on stratocumulus cloud properties. This method shows that changes in droplet size previously attributed to aerosol are actually due to increases in evaporation from the ocean surface due to high surface wind speeds. However, when this is accounted for, a clear impact of giant cloud condensation nuclei is observed, reducing cloud droplet number concentrations by initiating precipitation in polluted clouds. By isolating the causal aerosol impact on clouds from confounding factors, this method provides a pathway to improved constraints on the human forcing of the climate, whilst also demonstrating how marine aerosols limit the effectiveness of anthropogenic aerosol perturbations.
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Journal articleSnodgrass C, Epifani EM, Tubiana C, et al., 2026,
Considerations on the process of target selection for the Comet Interceptor mission
, Icarus, Vol: 447, ISSN: 0019-1035Comet Interceptor is an ESA science mission with payload contributions from ESA Member States and with an international participation by JAXA. It is the first mission that is being designed, built, and potentially launched before its target is known. This approach will enable the spacecraft to perform the first mission to a Long Period Comet from the Oort Cloud, as these comets have fleeting visits to the inner Solar System lasting only months to years from first discovery, too short for the usual process of mission development to be followed. In this paper we describe a number of factors that need to be considered in selecting a target for the mission, including scientific, orbital, spacecraft and instrument constraints, and discussion of different prioritisation strategies. We find that, in the case where we have a choice of targets, our decisions will mostly be driven by orbital information, which we will have relatively early on, with information on the activity level of the comet an important but secondary consideration. As cometary activity levels are notoriously hard to predict based on early observations alone, this prioritisation / decision approach based more on orbits gives us confidence that a good comet that is compatible with the spacecraft constraints will be selectable with sufficient warning time to allow the mission to intercept it.
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Conference paperGryspeerdt E, Driver OGA, Marjani S, et al., 2026,
Aircraft as a natural experiment on ice clouds
<jats:p>Aerosol impacts on ice clouds remain a highly uncertain component of the effective radiative forcing from aerosol-cloud interactions, with models simulating a wide range of responses. Developing observational constraints for these aerosol-cloud effects is challenging. The low aerosol concentrations involved hinder their direct observation and the meteorological conditions that affect cloud properties (such as temperature and updraught speed) also impact ice crystal number, limiting its use for inferring information about aerosol. Variations in meteorological conditions can also impact cloud and aerosol properties together, obscuring the causal impact of aerosol on cloud.Similar to the use of ship emitted aerosol and the resulting 'shiptrack' cloud perturbation to understand aerosol-cloud interactions in liquid clouds, here we use aircraft to understand the response of ice clouds to aerosol perturbations. Aircraft release water, aerosol and heat into the atmosphere as they fly, creating contrails in clear sky if conditions are suitable and perturbing existing clouds they fly through. The perturbation sizes vary with aircraft type, allowing a more detailed assessment of cloud responses.Using a range of satellite data and ground-based radar observations, we composite contrails and aircraft impacts on existing clouds under a variety of conditions from a range of different aircraft types. We see that contrails formed from different aircraft types have varying lifetimes, consistent with an aerosol effect that increases cloud lifetime. Impacts on existing clouds vary significantly with time since the perturbation and meteorological conditions, highlighting the importance of the background cloud conditions. We also demonstrate how non-aerosol effects can be isolated and removed, to better constrain the impact of aerosols and aircraft on ice clouds and climate. </jats:p>
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Conference paperMaruhashi J, Marjani S, Driver O, et al., 2026,
Success and failure of contrail models: a flight-by-flight investigation using satellite observations
<jats:p>A realistic quantification of aviation’s net global climate impact depends on how well models represent aviation-induced aerosols (e.g., soot and sulfate) and their dual role: contributing to net warming through the formation of persistent ice clouds (contrails) and contributing to cooling by altering the microphysical properties of existing liquid clouds. Here, we focus on the warming pathway. Persistent contrails are estimated to produce warming over a year comparable to the warming from aviation CO₂ accumulated over several decades [1] and may account for ~2% of the total anthropogenic surface temperature increase since pre-industrial times [2]. Given their importance, contrails must be modelled both accurately and efficiently to support operational mitigation and to track aviation’s climate impact.The Contrail Cirrus Prediction (CoCiP) tool is a widely used Lagrangian model that predicts contrail formation and evolution on a flight-by-flight basis. CoCiP is integrated into the Non-CO₂ Aviation Effects Tracking System (NEATS), which supports compliance with recent European reporting requirements for non-CO₂ aviation effects. Despite its broad adoption, CoCiP has been shown to underestimate lifetime-integrated optical depth relative to higher-fidelity models [3], motivating further evaluation against observations.We analyze ~500 flights from 2025 that flew through the UK and surrounding region (approximately 48°N-63°N, 20°W-4°E) that have been contrail-matched using detections from the Earth Cloud Aerosol and Radiation Explorer (EarthCARE) mission. For each flight, we run CoCiP and compare its output at the advected waypoint closest to the satellite-detected contrail at the detection time. We find that CoCiP fails to predict a contrail for roughly half of the cases. For ~20% of flights, contrail formation is not expected based on the Schmidt–Appleman criterion, which depends on both atmospheric and aircraft character
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Conference paperSteinwand V, Stephenson P, Lewis Z, et al., 2026,
Cometary ion dynamics under weakly outgassing conditions
, EGU General Assembly 2026, Publisher: European Geosciences Union -
Journal articleHuang Z, Velli M, Panasenco O, et al., 2026,
Evidence of 5 minute Oscillations from Parker Solar Probe
, Astrophysical Journal Letters, Vol: 999, ISSN: 2041-8205The Sun’s surface vibrates in characteristic 5 minute oscillations, known as p-modes, generated by sound waves trapped within the convection zone. Although these oscillations have long been hypothesized to reach into the solar wind, direct in situ evidence has remained elusive, even during previous close encounters by Parker Solar Probe (PSP). Here, we present strong in situ evidence of 5 minute oscillations in the upper solar corona, based on observations from PSP’s three closest perihelia. In two events at 9.9 solar radii (R<inf>⊙</inf>), we identify statistically significant (∼6σ) 3.1–3.2 mHz peaks in the magnetic field power spectrum, each appearing as a large-amplitude, spherically polarized Alfvénic wave train lasting approximately 35 minutes. These results demonstrate that global solar oscillations can reach the solar wind.
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Journal articleSchwartz SJ, Trattner KJ, Raptis S, et al., 2026,
Energy Partition at a Collisionless Supercritical Quasi-Parallel Shock
, Journal of Geophysical Research Space Physics, Vol: 131, ISSN: 2169-9380Shocks in collisionless astrophysical plasmas redistribute some of the incident flow energy into both thermal and non-thermal energy. Quantifying the partition of that energy amongst various particle species or their sub-populations, and electromagnetic energy, represents a fundamental goal of shock physics. It embodies the role of the equation of state for the system. Here we apply a framework to assess all the incident and downstream energy fluxes at a crossing of Earth's bow shock for which the upstream magnetic field was roughly aligned with the shock normal direction. Such quasi-parallel shocks are known to be non-steady and to produce significant populations of suprathermal particles. We quantify the evolution of all the important carriers of energy flux through the shock region. We sub-divide the proton population into thermal, suprathermal, and energetic components in order to investigate the shock's efficiency in energizing the nonthermal particles. While the largest energy fluxes are found in the incident proton ram energy and downstream proton thermal enthalpy fluxes, a significant suprathermal population pervades the regions both up- and downstream. We also evaluate the energy fluxes attributable to fluctuations in the fluid and field parameters.
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Journal articleZhao J, Bowen TA, Bale SD, et al., 2026,
Observations of Transition from Imbalanced to Balanced Kinetic Alfvénic Turbulence
, Astrophysical Journal Letters, Vol: 999, ISSN: 2041-8205We report observations of solar wind turbulence derived from measurements by the Parker Solar Probe. Our findings reveal the emergence of finite magnetic helicity within the transition range of the turbulence, aligning with signatures of kinetic Alfvén waves (KAWs). Notably, as the wave scale transitions from superion to subion scales, the ratio between KAWs with opposite signs of magnetic helicity initially increases from approximately one to 6.5, before decreasing back to one. This observation provides, for the first time, compelling evidence for the transition from imbalanced to balanced kinetic Alfvénic turbulence.
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Journal articleWivell L, Dougherty MK, Masters A, 2026,
The dynamic inducing magnetic field signal at Triton
, Geophysical Research Letters, Vol: 53, ISSN: 0094-8276Triton, Neptune's largest moon, is suspected of harboring a subsurface ocean. Detecting sub-surface oceans requires measuring the ocean's induced magnetic field, typically exploiting common frequencies at which the field environment of the moon changes, in this case Triton's path through Neptune's magnetosphere. Triton's orbit around Neptune, whilst nearly completely circular, is highly inclined, with an inclination of approximately 157° to Neptune's equator. This results in a rotation signal strength and frequency which has significant orbital dependence, unlike at other ocean worlds. The work conducted in this study highlights how the inducing signal at Triton is dynamic in both power and frequency caused by Triton's high inclination. This means that there is a richer set of frequency signals than previously thought, that may be useful for induction studies. This work quantifies the effect that Triton's inclination has on the inducing signal, and rules out other potential sources of signal disruption.
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Journal articleMa B, Chen L, Wu D, et al., 2026,
The Spectral Features of Single-band Type III-like Radio Bursts Observed by PSP during Its First Nine Orbital Encounters
, Astrophysical Journal, Vol: 998, ISSN: 0004-637XThe spectral features of 1122 single-band type III-like radio bursts were analyzed statistically using data from the Parker Solar Probe (PSP) during the first nine orbital encounters. After excluding overlapping events, 923 bursts were classified into 706 complete-spectrum (CS) bursts and 217 incomplete-spectrum (IS) bursts depending on radiation completeness. The distribution of start frequency f<inf>st</inf> for IS events (20–54 MHz) was predicted by a lognormal fit. The higher cutoff frequency (f<inf>lo</inf> ∼ 1.2–1.6 MHz) than previous results may be attributed to the limitation of exciting conditions or the radial expansion of guiding magnetic flux tubes. Short durations (1–4 minutes) and low peak fluxes (∼10<sup>3</sup> sfu) indicate that most events are short-time weak bursts. The spectral index of duration versus frequency is near −1, which reflects the influence of velocity dispersion and radio-wave scattering. For the denoised spectra of CS events, the peak frequency of maximal flux (∼4.5 MHz) is obviously higher than those from STEREO (∼1 MHz) and WIND (∼ 2 MHz). This implies that the radiation may be the second or third harmonic wave rather than the fundamental wave. Statistical frequency drift rates follow the classical power-law relation (D<inf>abs</inf> ∝ f<sup>1.84</sup>) and are consistent with simulation results of typical type III radio bursts. CS and IS bursts show similarities in f<inf>lo</inf>, duration, and drift features, but obviously differ in the peak frequency of maximal flux. These results can provide a useful reference for further exploring the emission mechanisms of single-band type III-like radio bursts and the associated energetic electron acceleration processes.
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Journal articleLario D, Hu J, Balmaceda LA, et al., 2026,
The Major Solar Energetic Particle Event on 2024 May 20: Multispacecraft Observations of a Long-lasting Energetic Particle Reservoir
, Astrophysical Journal, Vol: 998, ISSN: 0004-637XThe fleet of spacecraft distributed across the inner heliosphere during 2024 May–June provided a unique opportunity to analyze, over a broad range of heliolongitudes, the effects produced by the complex sunspot group associated with Active Region 13664. The intense solar activity from 2024 May 8 to 2024 June 21 produced unusually elevated solar energetic particle (SEP) intensities observed at heliocentric distances ≲1 au by Solar Orbiter, Parker Solar Probe, STEREO-A, and near-Earth spacecraft. This activity resulted in a >40 day period of enhanced ≲10 MeV proton intensities spanning at least ∼170° in longitude. Among these events, the 2024 May 20 SEP event was remarkable for its high intensity and wide spatial extent. It was associated with a fast (≳1500 km s<sup>−1</sup>) halo coronal mass ejection (CME) and an X16.5 solar flare located ∼171° in longitude from Earth. Near Earth, the event produced a long-lasting ∼100 MeV proton intensity enhancement with energy spectra flattening between 30 and 80 MeV. It also led to the formation of an energetic particle reservoir that persisted for ∼2 weeks and extended across at least ∼170° in longitude. Several mechanisms contributed to the broad longitudinal spread of SEPs and formation of the energetic particle reservoir, including acceleration at an extended CME-driven shock, particle drifts along the heliospheric current sheet, particle reflection and redistribution caused by the merging of preceding CMEs beyond 1 au, and predominantly cross-field particle transport processes.
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Journal articleJia H, Quaas J, Kroese W, et al., 2026,
Optimal choice of proxy for cloud condensation nuclei reduces uncertainty in aerosol-cloud-climate forcing
, Science Advances, Vol: 12, ISSN: 2375-2548Aerosol-cloud interactions (ACI) remain the largest uncertainty in anthropogenic climate forcings. Observation-based estimates of instantaneous radiative forcing from ACI (RFaci; the Twomey effect) rely on the choice of aerosol quantities as proxies for cloud condensation nuclei (CCN) concentrations, which differ in their ability to represent cloud-base CCN and data accuracy. Using diverse observations and aerosol-climate models, we evaluate the utility of different proxies with two independent approaches. Both approaches reveal that surface CCN exhibits the smallest bias in predicting RFaci (+5%), followed by aerosol index, surface sulfate and column CCN with similar biases of +25%, while aerosol optical depth and column sulfate show the largest biases (−60% and +92%). Constraining RFaci with the optimal proxy reduces uncertainty from 66 to 43%, yielding a less negative RFaci (−1.0 W m−2) than the unconstrained case (−1.2 W m−2). Our findings highlight the crucial role of proxy constraint in reconciling and improving RFaci estimates.
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Journal articleBianco JS, Tenerani A, Gonzalez C, et al., 2026,
Evolution of an Alfvén wave–driven proton beam in the expanding solar wind
, The Astrophysical Journal, Vol: 998, ISSN: 0004-637XWe investigate the self-consistent formation and long-term evolution of proton beams in the expanding solar wind using an ensemble of one-dimensional hybrid expanding box simulations. Initial conditions are chosen to represent a range of plasma states observed by the Helios spacecraft at 0.3 au, including an amplitude-modulated Alfvén wave that nonlinearly drives a proton beam aligned with the magnetic field. We compare simulation results with solar wind data out to 1.5 au and show that our model reproduces key observed features of proton beams on average, such as the radial evolution of the drift and the relative core-to-beam density ratio. These findings support the theory that the observed evolution of the proton beam drift in the solar wind is determined by kinetic instabilities. More broadly, our results indicate that the interplay between nonlinear Alfvén wave dynamics, expansion effects, and kinetic instabilities plays a fundamental role in solar wind dynamics, with implications for interpreting solar wind heating rate estimates.
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Journal articleWilson Kemsley S, Nowack P, Ceppi P, 2026,
Recent cloud controlling factor analyses indicate higher climate sensitivity
, Geophysical Research Letters, Vol: 53, ISSN: 0094-8276Cloud feedback is a dominant source of uncertainty in climate model estimates of equilibrium climate sensitivity (ECS). Cloud controlling factor analysis can observationally constrain cloud feedback. For the first time, we use separate rather than unified frameworks to assess high- and low-cloud feedbacks and constrain the net cloud feedback and subsequently, the ECS. We find a robustly positive cloud feedback (i.e., a negative feedback is <0.5% probable), indicating that clouds amplify global warming. We assess the individual and combined impacts of our cloud feedback constraints on ECS using three approaches. Two indicate an upward ECS shift with reduced uncertainty, preserving ECS–feedback correlations but using cloud feedback as a single line of evidence. The third, a Bayesian framework combining multiple lines of evidence, also suggests a higher ECS but with a smaller increase and broader confidence range.
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Conference paperWalach MT, Lam MM, Themens DR, et al., 2026,
Challenges for ionosphere-thermosphere science
, Pages: 36-42, ISSN: 1366-8781Report on the RAS Specialist Discussion Meeting about one of the grand challenges for Earth system scientists.
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Journal articleFargette N, Eastwood JP, Phan TD, et al., 2026,
Fluid and kinetic properties of the near-sun heliospheric current sheet
, The Astrophysical Journal, Vol: 997, ISSN: 0004-637XThe heliospheric current sheet (HCS) is an important large-scale structure of the heliosphere, and, for the first time, the Parker Solar Probe (PSP) mission enables us to study its properties statistically, close to the Sun. We visually identify the 39 HCS crossings measured by PSP below 50 R⊙ during encounters 6–21, and investigate the occurrence and properties of magnetic reconnection, the behavior of the spectral properties of the turbulent energy cascade, and the occurrence of kinetic instabilities at the HCS. We find that 82% of the HCS crossings present signatures of reconnection jets, showing that the HCS is continuously reconnecting close to the Sun. The proportion of inward and outward jets depends on heliocentric distance, and the main HCS reconnection X-line has a higher probability of being located close to the Alfvén surface. We also observe a radial asymmetry in jet acceleration, where inward jets do not reach the local Alfvén speed, contrary to outward jets. We find that turbulence levels are enhanced in the ion kinetic range, consistent with the triggering of an inverse cascade by magnetic reconnection. Finally, we highlight the ubiquity of magnetic hole trains in the high-β environment of the HCS, showing that the mirror mode instability plays a key role in regulating the ion temperature anisotropy in HCS reconnection. Our findings shed new light on the properties of magnetic reconnection in the high-β plasma environment of the HCS, its interplay with the turbulent cascade, and the role of the mirror mode instability.
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Journal articleClear CP, Uylings P, Raassen T, 2026,
Calculated oscillator strengths and transition probabilities of singly ionised nickel (Ni II)
, Astronomy and Astrophysics (A & A), Vol: 706, ISSN: 0004-6361Aims. This work reports calculated transition probabilities for spectral lines of singly ionised nickel (Ni II) incorporating newly determined experimental energy levels, addressing critical gaps in atomic data required for astrophysical spectroscopy and plasma diagnostics.Methods. Transition probabilities of Ni II were calculated using the semi-empirical orthogonal operator method for both odd and even energy levels. Calculated eigenvalues were fine-tuned to experimental energy levels, determined using Fourier transform spectroscopy, further increasing the accuracy of these calculated transition probabilities.Results. In total, transition probabilities have been calculated for nearly 118 000 electric dipole transitions between 361 even and 735 odd levels. The resulting transition probabilities show strong agreement with existing experimental and semi-empirical data, while offering improved consistency and coverage across a wide range of line strengths. The calculated transitions span the far-infrared to the vacuum ultraviolet spectral regions, providing extensive coverage for astrophysical applications. This dataset significantly enhances the calculated atomic data available for Ni II and represents a critical contribution to the advancement of our understanding of astrophysical phenomena through improved spectroscopic analysis.
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Journal articleHadid LZ, Chust T, Wahlund JE, et al., 2026,
Evidence of an Extended Alfvén Wing System at Enceladus: Cassini's Multi-Instrument Observations
, Journal of Geophysical Research Space Physics, Vol: 131, ISSN: 2169-9380We 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 (Formula presented.) ((Formula presented.) 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.
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