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Journal articleLewis H, Eastwood J, Phan T, et al., 2026,
Parker solar probe observations of a flux rope embedded in a near-sun heliospheric current sheet magnetic reconnection exhaust
, The Astrophysical Journal (ApJ), Vol: 1002, ISSN: 0004-637XIn situ observations by Parker Solar Probe (PSP) suggest that the heliospheric current sheet (HCS) undergoes near-continuous magnetic reconnection close to the Sun, in stark contrast to scarce observations of this phenomenon in the HCS at 1 AU. Situated at the boundary between sectors of opposite interplanetary magnetic field (IMF) polarity, reconnection in the HCS has important consequences for magnetic topology and plasma dynamics in the slow solar wind. We report observations of a reconnection outflow in theHCS near the Alfv´en transition region in PSP’s 17th solar encounter, featuring plasma jetting, proton temperature enhancement, and electron heat flux dropout. Embedded within the exhaust is a non-force-free flux rope plasmoid exhibiting counterstreaming strahl electrons, indicating connection at both ends to the Sun in an otherwise disconnected region of magnetic field. The flux rope features diminished isotropic protontemperature and lower bulk speed compared to the remainder of the HCS exhaust. Its oblique orientation and different plasma properties imply the flux rope originates from a different reconnection site to the HCS exhaust, suggesting PSP has intercepteda flux-rope-like streamer blob produced at the helmet streamer. Remote observations show several comparable blobs travelling in a distant coronal ray, demonstrating the possibility that the in situ flux rope is a streamer blob. The combination of in situ andremote observations demonstrate the role of magnetic reconnection in HCS dynamics, contributing to a growing understanding of this fundamental mechanism and its impact on the young solar wind.
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Journal articleHorne RB, Angling MJ, Attrill GDR, et al., 2026,
The May 2024 geomagnetic storm: UK experience and perspective
, Royal Society Open Science, Vol: 13, ISSN: 2054-5703The May 2024 geomagnetic storm was the largest for over 20 years. The storm was categorized as a ‘low-level’ G5, where G5 is the highest on the National Oceanic and Atmospheric Administration (NOAA) scale for geomagnetic storms, yet the individual solar eruptive events were not particularly severe, and the observed impacts were relatively minor. The impacts that were observed were due to the combined and sustained effect of five successive earthward-directed coronal mass ejections (CMEs) which drove the storm. The event exposed the weakness of the current storm classification system which does not discriminate between low impact and high impact G5 events; it exercised the UK Met Office forecasting system, communications and UK preparedness; and it highlighted key areas that need to be addressed, particularly relating to national power supplies, space traffic management, aviation, forecasting and data gaps. Here, we set out what happened, record some of the key impacts, discuss what went well and what needs to be improved. We make 14 recommendations relevant to four government departments, so that the UK can be better prepared for a low-probability, high-impact space weather event described in the reasonable worst-case scenario that informs the national risk register.
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Journal articleKelly H, Archer M, Eastwood J, et al.,
Superposition of doppler-shifting magnetopause Kelvin-Helmholtz modes through dynamic mode decomposition of a global MHD simulation
, Geophysical Research Letters, ISSN: 0094-8276 -
Journal articleErgun RE, Vo T, Qi Y, et al., 2026,
Evidence of a Subkinetic Spectral Break in a Strongly Turbulent Collisionless Plasma
, Astrophysical Journal, Vol: 1001, ISSN: 0004-637XWe investigate the magnetic (B) and electric (E) field spectra in the dissipation range of strong turbulence of a collisionless plasma. This investigation, which is relevant to turbulence studies in many astrophysical settings, is enabled by high-resolution measurements from the four-spacecraft Magnetospheric Multiscale (MMS) mission in the Earth’s magnetotail. B and E spectra are derived as a function of the product of the wave number and electron skin depth (|k| d<inf>e</inf>) using a novel technique that employs time-delay analysis on multiple intervals of B and E. Using the MMS tetrahedral formation with close (several d<inf>e </inf>) spacing, velocities of B and E signals can be derived so that native frequency-based spectra can be accurately translated to k spectra. The most important finding is a mathematically significant break in the B spectral index that appears at |k| d<inf>e</inf> ≈ 1. In the subion range, which spans from the ion inertial length (d<inf>ι </inf>) to d<inf>e </inf>, the B spectral index is −2.35, then steepens to − 3.13 at sub-d<inf>e </inf> scales. As expected from previously derived frequency spectra, E has a particularly shallow spectral index (−0.67) in the subion range. At scales smaller than d<inf>e </inf> and/or the electron thermal gyroradius (ρ<inf>e </inf>), the E spectral index steepens to −2.73. Spectral breaks in both B and E in the dissipation range indicate a change in the physical dissipation processes from ion to electron domination at |k| d<inf>e</inf> ≈ 1. We also confirm that at |k| ρ<inf>e</inf> > ~ 2, the energy density of B and E approaches equipartition, suggesting that energy transfer is near complete.
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Journal articleGuo J, Xie X, Myhre G, et al., 2026,
Distinct drivers of recent seasonal precipitation increase over Central Asia: roles of anthropogenic aerosols and greenhouse gases
, Atmospheric Chemistry and Physics, Vol: 26, Pages: 5169-5184, ISSN: 1680-7316Observational evidence reveals a pronounced wetting trend over Central Asia in recent decades, with the most substantial increases occurring during winter and summer. Yet the extent to which the drivers of these changes differ seasonally remains unknown. Here, we use single-forcing experiments from the Precipitation Driver and Response Model Intercomparison Project (PDRMIP) to examine the effects of various external forcings on winter and summer precipitation across Central Asia and to explore the physical mechanisms underlying seasonal precipitation changes. We find that greenhouse gas (GHG) forcing mainly increases winter precipitation by enhancing atmospheric moisture content through warming. In contrast, in summer, Asian sulfate aerosols enhance precipitation by modulating the westerly jet, which strengthens atmospheric moisture transport into the region. Asian black carbon exerts an opposing influence that partially offsets the sulfate-induced effect. Further attribution analysis based on CMIP6 simulations reinforces these sensitivity results and shows that GHG forcing is the primary driver of winter precipitation increases whereas anthropogenic aerosols dominate summer trends. Future CMIP6 projections suggest that under moderate- to high-emission scenarios, winter precipitation will continue to rise due to increasing GHG concentrations, while summer precipitation may decline across much of Central Asia as a result of reduced aerosol emissions following Asian clean air policies. These findings highlight a distinct seasonality in the drivers of recent precipitation increase and suggest a plausible divergence in future winter and summer precipitation trends.
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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 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 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 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 articleZelinka MD, Myers TA, Qin Y, et al., 2026,
Recent cloud trends and extremes reaffirm established bounds on cloud feedback and aerosol-cloud interactions
, Communications Earth & Environment -
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 articleDing M, Darvariu V-A, Ryabtsev AN, et al., 2026,
Accelerating atomic fine structure determination with graph reinforcement learning
, Communications Physics<jats:title>Abstract</jats:title> <jats:p> Atomic data determined by analysis of observed atomic spectra are essential for plasma diagnostics. For each low-ionisation open d- and f-subshell atomic species, around 10 <jats:sup>3</jats:sup> fine structure energy levels can be determined through years of analysis of 10 <jats:sup>4</jats:sup> observable spectral lines. We propose a partial automation of this task by casting the analysis procedure as a Markov decision process and solving it by graph reinforcement learning using reward functions partly learned on historical human decisions. In our evaluations on existing spectral line lists and theoretical calculations for Co II, Nd II and Nd III, hundreds of energy levels were identified and determined in hours, agreeing with published values in 95% of cases for Co II and 54–87% for Nd II and Nd III. As the current efficiency in atomic fine structure determination struggles to meet growing atomic data demands, our artificial intelligence approach sets the stage for closing this gap. </jats:p>
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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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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 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 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 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, Pages: 194-194, ISSN: 0004-637X<jats:title>Abstract</jats:title> <jats:p>We 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.</jats:p>
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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 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 (Formula presented.) % 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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Journal articleHorbury T, 2026,
The IMAP magnetometer
, Space Science Reviews, ISSN: 0038-6308The magnetometer (MAG) is one of the ten scientific instruments on the Interstellar Mapping and Acceleration Probe (IMAP), which will take in situ and remote measurements from a Sun- Earth L1 halo orbit. MAG contributes to IMAP science goals of investigating the acceleration and propagation of energetic particles, as well as providing real-time space weather monitoringdata. The magnetometer is a conventional dual sensor fluxgate instrument with a noise floor under 10 pT at 1 Hz, taking science measurements continuously at 2 vectors/s as well as a burst mode of 64 vectors/s for at least 8 hours per day. It also provides a real-time space weathermonitoring product at 4 second cadence. We describe the requirements, design and performance of the instrument, including a novel lossless compression algorithm. Data products, processing and calibration plans are presented.
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Journal articleWivell L, Dougherty MK, Masters A, 2026,
Inductive response of Enceladus' ice shell and potentially stratified ocean
, Earth and Space Science, Vol: 13, ISSN: 2333-5084Saturn's moon Enceladus harbors a global subsurface ocean beneath its icy crust. Understanding the structure and composition of this ocean and ice is critical to assessing its potential habitability. Modern electromagnetic (EM) sounding techniques, which measure a celestial body's induced response to external electromagnetic fields, offer a powerful tool for probing internal structures. These techniques are well-established for Earth and the Moon, modeled for Europa, and here evaluated for Enceladus. By modeling higher frequency range (1 mHz−1 kHz), which sound to shallower depths than lower frequencies, this study shows that induction can provide a constraint on ice composition. The induced response also gives insight into other ice-shell properties, including potential water layers, as well as different stratified ocean conditions. The findings of this study highlight the potential for future missions to use EM sounding to constrain properties of the ice-shell, including composition, as well as identifying potential ocean stratification.
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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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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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