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Journal articlePayne DS, Swisdak M, Eastwood JP, et al., 2025,
In-situ observations of the magnetothermodynamic evolution of electron-only reconnection
, Communications Physics, Vol: 8Field-particle energy exchange is important to the magnetic reconnection process, but uncertainties regarding the time evolution of this exchange remain. We investigate the temporal dynamics of field-particle energy exchange during magnetic reconnection, using Magnetospheric Multiscale mission observations of an electron-only reconnection event in the magnetosheath. The electron energy is in local minimum at the x-line due to a density depletion, while the magnetic energy is in local maximum due to a guide field enhancement. The electromagnetic energy transport comes almost entirely from guide field contributions and is confined within the reconnection plane, while the most significant contribution to electron energy transport is independent of the drift velocity with additional out-of-plane signatures. Multi-spacecraft analysis suggests that the guide field energy is decreasing while the electron density is increasing, both evolving such that the system is moving toward a more uniform distribution of magnetic and thermal energy.
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Journal articleZhang J, Chen YS, Gryspeerdt E, et al., 2025,
Radiative forcing from the 2020 shipping fuel regulation is large but hard to detect
, Communications Earth and Environment, Vol: 6Reduction in aerosol cooling unmasks greenhouse gas warming, exacerbating the rate of future warming. The strict sulfur regulation on shipping fuel implemented in 2020 (IMO2020) presents an opportunity to assess the potential impacts of such emission regulations and the detectability of deliberate aerosol perturbations for climate intervention. Here we employ machine learning to capture cloud natural variability and estimate a radiative forcing of +0.074 ±0.005 W m−2 related to IMO2020 associated with changes in shortwave cloud radiative effect over three low-cloud regions where shipping routes prevail. We find low detectability of the cloud radiative effect of this event, attributed to strong natural variability in cloud albedo and cloud cover. Regionally, detectability is higher for the southeastern Atlantic stratocumulus deck. These results raise concerns that future reductions in aerosol emissions will accelerate warming and that proposed deliberate aerosol perturbations such as marine cloud brightening will need to be substantial in order to overcome the low detectability.
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Journal articleDeca J, Divin A, Stephenson P, et al., 2025,
A fully kinetic perspective on weakly active comets: asymmetric outgassing
, Planetary and Space Science, Vol: 258, ISSN: 0032-0633The European Space Agency’s Rosetta mission measured the complex plasma environment surrounding comet 67P/Churyumov-Gerasimenko for more than two years. In this work, the collisionless dynamics of the plasma interaction during the comet’s weakly outgassing phases is investigated through a fully kinetic semi-implicit particle-in-cell approach. The effects of an asymmetric outgassing profile with respect to the upstream plasma conditions are compared with a spherically symmetric Haser model. The three-dimensional shape of the plasma density and the parallel acceleration potential are used as primary measures. It is found that the four-fluid coupled system is not majorly distorted. The different components of the potential structure can be associated with the large-scale behavior and density profiles of the four simulated plasma species. The implications for the acceleration and cooling of electrons within the cometary plasma environment are identified by contrasting the differences in the shape of the acceleration potential between the distinct asymmetric outgassing models. The analysis provides a detailed overview that can help interpret past Rosetta plasma measurements and could be key to help disentangle the physical drivers active in the plasma environment of comets visited by future exploration missions.
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Journal articleFujita R, Graven H, Zazzeri G, et al., 2025,
Global Fossil Methane Emissions Constrained by Multi-Isotopic Atmospheric Methane Histories
, Journal of Geophysical Research: Atmospheres, Vol: 130, ISSN: 2169-897XThe global CH4 budget of sources and sinks is highly uncertain, particularly the emissions from specific sources such as fossil fuels (FF) or agriculture. Here, we estimate plausible global CH4 source and sink scenarios using historical observations and simulations of atmospheric CH4 mole fraction and its stable isotopic (δ13C-CH4, δD-CH4) and radiocarbon (Δ14C-CH4) composition, combining constraints from all these tracers for the first time. We employ a one-box model along with a Monte Carlo particle filter technique, explicitly exploring the impact of each isotopic constraints and uncertainties in prior CH4 source and sink parameters on posterior sectorial source fractions. We find our posterior anthropogenic FF emissions at the global scale are 30% lower than previous isotope-based studies. Our analysis suggests previous δ13C-CH4-based studies are potentially biased because the current database-derived estimate of the global mean biogenic δ13C-CH4 source signature is too low and/or current sink-weighted total carbon kinetic isotope effect is underestimated. We find modern atmospheric Δ14C-CH4 data constrains lower global FF emissions after 1980s, which is contrary to the most recent finding that utilized atmospheric Δ14C-CH4 data, but supported by an independent estimate of global nuclear 14CH4 emissions. Our multi-isotopic constraints align with CH4-only inversion results, while reducing their uncertainties with greater robustness against different prior emission scenarios. We find strong constraints not only on FF emissions but also other key sources and sinks, showing that long-term multi-isotopic observations are critical for refining the global CH4 budget and developing effective CH4 emission mitigation strategies.
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Journal articleSimpson IR, Shaw TA, Ceppi P, et al., 2025,
Confronting Earth System Model trends with observations.
, Sci Adv, Vol: 11Anthropogenically forced climate change signals are emerging from the noise of internal variability in observations, and the impacts on society are growing. For decades, Climate or Earth System Models have been predicting how these climate change signals will unfold. While challenges remain, given the growing forced trends and the lengthening observational record, the climate science community is now in a position to confront the signals, as represented by historical trends, in models with observations. This review covers the state of the science on the ability of models to represent historical trends in the climate system. It also outlines robust procedures that should be used when comparing modeled and observed trends and how to move beyond quantification into understanding. Finally, this review discusses cutting-edge methods for identifying sources of discrepancies and the importance of future confrontations.
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Journal articleDriver O, Stettler MEJ, Gryspeerdt E, 2025,
Factors limiting contrail detection in satellite imagery
, Atmospheric Measurement Techniques, ISSN: 1867-1381 -
Journal articleMasters A, Modolo R, Roussos E, et al., 2025,
Magnetosphere and Plasma Science with the Jupiter Icy Moons Explorer
, Space Science Reviews, ISSN: 0038-6308 -
Journal articleTrotta D, Dimmock A, Hietala H, et al., 2025,
An Overview of Solar Orbiter Observations of Interplanetary Shocks in Solar Cycle 25
, Astrophysical Journal, Supplement Series, Vol: 277, ISSN: 0067-0049Interplanetary (IP) shocks are fundamental constituents of the heliosphere, where they form as a result of solar activity. We use previously unavailable measurements of IP shocks in the inner heliosphere provided by Solar Orbiter, and present a survey of the first 100 shocks observed in situ at different heliocentric distances during the rising phase of solar cycle 25. The fundamental shock parameters (shock normals, shock normal angles, shock speeds, compression ratios, Mach numbers) have been estimated and studied as a function of heliocentric distance, revealing a rich scenario of configurations. Comparison with large surveys of shocks at 1 au shows that shocks in the quasi-parallel regime and with high speed are more commonly observed in the inner heliosphere. The wave environment of the shocks has also been addressed, with about 50% of the events exhibiting clear shock-induced upstream fluctuations. We characterize energetic particle responses to the passage of IP shocks at different energies, often revealing complex features arising from the interaction between IP shocks and preexisting fluctuations, including solar wind structures being processed upon shock crossing. Finally, we give details and guidance on the access use of the present survey, available on the EU-project “Solar Energetic Particle Analysis Platform for the Inner Heliosphere” website. The algorithm used to identify shocks in large data sets, now publicly available, is also described.
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Journal articleLee D, Sparrow SN, Willeit M, et al., 2025,
Quantifying CO₂ and non‐CO₂ contributions to climate change under 1.5°C and 2°C adaptive emission scenarios
, Earth's Future, Vol: 13, ISSN: 2328-4277The individual contributions of various human-induced forcings under scenarios compatible with the Paris Agreement targets are highly uncertain. To quantify this uncertainty, we analyze three types of models with physical parameter perturbed large ensembles under global warming levels of 1.5 and 2.0°C. The scenarios use adaptive CO2 emissions, while non-CO2 emissions are prescribed. The residual emission budgets in the scenarios are measured in terms of CO2 forcing equivalent (CO2-fe). Our simulations quantify approximately 0.8 (0.2–1.3 for a 90% confidence interval) and 1.9 (0.9–3.0) TtCO2-fe for the 1.5 and 2.0°C targets by the end of the 21st century. About 37.5% (73.7%) of the budget for 1.5°C (2.0°C) originates from the CO2 emission pathways, highlighting the importance of non-CO2 forcings. Aerosols dominate the uncertainty in non-CO2 contributions to global responses in both temperature and precipitation. Our modeling results underline the need to constrain the response to each climate forcing, particularly aerosol, to build an accurate mitigation and adaptation plan under the pledges of the Paris Agreement. Moreover, we demonstrate robust differences in global and regional temperature and precipitation responses between the higher and lower CO2 emission scenarios, highlighting the significance of carbon neutrality.
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Journal articleMuro GD, Cohen CMS, Xu Z, et al., 2025,
Radial Dependence of Ion Fluences in the 2023 July 17 Solar Energetic Particle Event from Parker Solar Probe to STEREO and ACE
, Astrophysical Journal, Vol: 981, ISSN: 0004-637XIn the latter moments of 2023 July 17, the solar active region (AR) 13363, near the southwestern face of the Sun, was undergoing considerable evolution, which resulted in a significant solar energetic particle (SEP) event measured by Parker Solar Probe’s Integrated Science Investigation of the Sun (ISeIS) and near-Earth spacecraft. Remote observations from GOES and CHASE captured two M5.0+ solar flares that peaked at 23:34 and 00:06 UT from the source region. In tandem, STEREO COR2 first recorded a small, narrow coronal mass ejection (CME) emerging at 22:54 UT and then saw a major halo CME emerge at 23:43 UT with a bright, rapidly expanding core and CME-driven magnetic shock with an estimated speed of ∼1400 km s−1. Parker Solar Probe was positioned at 0.65 au, near-perfectly on the nominal Parker spiral magnetic field line, which connected Earth and the AR for a 537 km s−1 ambient solar wind speed at L1. This fortuitous alignment provided the opportunity to examine how the SEP velocity dispersion, energy spectra, elemental composition, and fluence varied from 0.65 to 1 au along a shared magnetic connection to the Sun. We find a strong radial gradient, which is best characterized for H and He as r−4.0, and most surprisingly, is stronger for O and Fe, which is better described by r−5.7
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Journal articleDrake JF, Antiochos SK, Bale SD, et al., 2025,
Magnetic Reconnection in Solar Flares and the Near-Sun Solar Wind
, Space Science Reviews, Vol: 221, ISSN: 0038-6308An overview is presented of our current understanding and open questions related to magnetic reconnection in solar flares and the near-sun (within around 20Rs) solar wind. The solar-flare-related topics include the mechanisms that facilitate fast energy release and that control flare onset, electron energization, ion energization and abundance enhancement, electron and ion transport, and flare-driven heating. Recent observations and models suggesting that interchange reconnection of multipolar magnetic fields within coronal holes could provide the energy required to drive the fast solar wind are also discussed. Recent in situ observations that reconnection in the heliospheric current sheet close to the sun drives energetic ions are also presented. The implications of in situ observations of reconnection in the Earth space environment for understanding flares are highlighted. Finally, the impact of emerging computational and observational tools for understanding flare dynamics are discussed.
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Journal articleBeth A, Galand M, Modolo R, et al., 2025,
Ionosphere of Ganymede: Galileo observations versus test particle simulation
, Monthly Notices of the Royal Astronomical Society, ISSN: 0035-8711 -
Journal articleGrimmich N, Pöppelwerth A, Archer MO, et al., 2025,
Investigation of the occurrence of significant deviations in the magnetopause location: solar-wind and foreshock effects
, Annales Geophysicae, Vol: 43, Pages: 151-173, ISSN: 0992-7689Common magnetopause models can predict the location of the magnetopause with respect to upstream conditions from different sets of input parameters, including solarwind pressure and the interplanetary magnetic field. However, recent studies have shown that some effects of upstream conditions may still be poorly understood since deviations between models and in situ observations beyond the expected scatter due to constant magnetopause motion are quite common. Using data from the three most recent multi-spacecraft missions to near-Earth space (Cluster, THEMIS, and MMS), we investigate the occurrence of these large deviations in observed magnetopause crossings from common empirical models. By comparing the results from different models, we find that the occurrence of these events appears to be model independent, suggesting that some physical processes may be missing from the models. To find these processes, we test whether the deviant magnetopause crossings are statistically associated with foreshocks and/or different solar-wind types and show that, in at least 40% of cases, the foreshock can be responsible for the large deviations in the magnetopause's location. In the case where the foreshock is unlikely to be responsible, two distinct classes of solar wind are found to occur more frequently in association with the occurrence of magnetopause deviations: the "fast"solar wind and the solarwind plasma associated with transients such as interplanetary coronal mass ejections. Therefore, the plasma conditions associated with these solar-wind classes could be responsible for the occurrence of deviant magnetopause observations. Our results may help to develop new and more accurate models of the magnetopause, which will be needed, for example, to accurately interpret the results of the upcoming SolarWind Magnetosphere Ionosphere Link Explorer (SMILE) mission.
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Journal articleSharan S, Dougherty M, Masters A, et al., 2025,
Viability of the early JUICE flyby trajectories to confirm ocean existence at Ganymede
, The Planetary Science Journal, ISSN: 2632-3338 -
Journal articlePanditharatne S, Brindley H, Cox C, et al., 2025,
Retrievals of water vapour and temperature exploiting the far-infrared: application to aircraft observations in preparation for the FORUM mission
, Atmospheric Measurement Techniques, Vol: 18, Pages: 717-735<jats:p>Abstract. We present the extension of the Rutherford Appleton Laboratory (RAL) Infrared Microwave Sounding (IMS) optimal estimation retrieval scheme to include the use of far-infrared channels in preparation for the upcoming Far-infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission. The IMS code has been previously applied to mid-infrared spectral radiances measured by the Infrared Atmospheric Sounding Instrument (IASI) to retrieve temperature and water vapour. Given this, the evolution and evaluation of the extended scheme is performed in two steps. First, clear-sky retrievals of temperature and water vapour are performed on IASI and FORUM simulations. Comparable retrieval biases are observed for retrievals of temperature and water vapour; however, there is an increase of ∼ 1 degree of freedom for water vapour and temperature for the FORUM configuration. Secondly, radiances observed from an aircraft flight in the upper troposphere are modified to match the FORUM spectral characteristics. Retrievals from these radiances using the modified code show a strong agreement with contemporaneous in situ measurements of the atmospheric state, reducing the root-mean-square error (RMSE) by 18 % for water vapour from the a priori, giving confidence in its performance. The extended IMS scheme is now available for use on FORUM observations and can be easily adapted to other far- and mid-infrared instrument configurations. </jats:p>
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Journal articleLiu Y-H, Hesse M, Genestreti K, et al., 2025,
Ohm's Law, the Reconnection Rate, and Energy Conversion in Collisionless Magnetic Reconnection
, Space Science Reviews -
Journal articleRivera YJ, Badman ST, Verniero JL, et al., 2025,
Differentiating the Acceleration Mechanisms in the Slow and Alfvénic Slow Solar Wind
, Astrophysical Journal, Vol: 980, ISSN: 0004-637XIn the corona, plasma is accelerated to hundreds of kilometers per second and heated to temperatures hundreds of times hotter than the Sun's surface before it escapes to form the solar wind. Decades of space-based experiments have shown that the energization process does not stop after it escapes. Instead, the solar wind continues to accelerate, and it cools far more slowly than a freely expanding adiabatic gas. Recent work suggests that fast solar wind requires additional momentum beyond what can be provided by the observed thermal pressure gradients alone, whereas it is sufficient for the slowest wind. The additional acceleration for fast wind can be provided through an Alfvén wave pressure gradient. Beyond this fast/slow categorization, however, a subset of slow solar wind exhibits high Alfvénicity that suggests that Alfvén waves could play a larger role in its acceleration compared to conventional slow wind outflows. Through a well-timed conjunction between Solar Orbiter and Parker Solar Probe (PSP), we trace the energetics of slow wind to compare with a neighboring Alfvénic slow solar wind stream. An analysis that integrates remote and heliospheric properties and modeling of the two distinct solar wind streams finds that Alfvénic slow solar wind behaves like fast wind, where a wave pressure gradient is required to reconcile its full acceleration, while non-Alfvénic slow wind can be driven by its nonadiabatic electron and proton thermal pressure gradients. Derived coronal conditions of the source region indicate good model compatibility, but extended coronal observations are required to effectively trace solar wind energetics below PSP's orbit.
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Journal articleMitchell JG, Christian ER, de Nolfo GA, et al., 2025,
Delay of Near-relativistic Electrons with Respect to Type III Radio Bursts throughout the Inner Heliosphere
, Astrophysical Journal, Vol: 980, ISSN: 0004-637XEnergetic electrons accelerated by solar eruptive events are frequently observed to have inferred injection times that appear significantly delayed with respect to electromagnetic emission including type III radio bursts. This is noteworthy because type III radio emission is produced by streaming suprathermal electrons, and thus this observed delay implies either a delayed injection/release of higher-energy electrons, compared with the suprathermal population, and/or a delay of the electrons observed in situ in transit through the interplanetary medium. A number of studies have investigated these delays with spacecraft located at 1 au. In this study, we examine energetic electron onsets and type III radio bursts observed by the Integrated Science Investigation of the Sun (IS⊙IS) and the FIELDS Radio Frequency Spectrometer instrument on Parker Solar Probe at a variety of heliocentric distances. With these observations, we can uniquely decouple the effects of acceleration and transport and shed light on the source of these delays. We present a survey of electron events observed by IS⊙IS within the first ∼6 yr of the mission, including their delays with respect to type III emission between ∼0.1 and 0.8 au. These results suggest that energetic electron delays with respect to type III radio bursts are not purely produced by a delayed injection/release as has been suggested, implying that transport processes play a role.
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Journal articleAmes F, Ferreira D, Czaja A, et al., 2025,
Ocean stratification impedes particulate transport to the plumes of Enceladus
, Nature Communications, ISSN: 2041-1723 -
Journal articleKokkola H, Tonttila J, Calderón SM, et al., 2025,
Model analysis of biases in the satellite-diagnosed aerosol effect on the cloud liquid water path
, Atmospheric Chemistry and Physics, Vol: 25, Pages: 1533-1543, ISSN: 1680-7316The response in cloud water content to changes in cloud condensation nuclei remains one of the major uncertainties in determining how aerosols can perturb cloud properties. In this study, we used an ensemble of large eddy simulations of marine stratocumulus clouds to investigate the correlation between cloud liquid water path (LWP) and the amount of cloud condensation nuclei. We compare this correlation directly from the model to the correlation derived using equations which are used to retrieve liquid water path from satellite observations. Our comparison shows that spatial variability in cloud properties and instrumental noise in satellite retrievals of cloud optical depth and cloud effective radii results in bias in the satellite-derived liquid water path. In-depth investigation of high-resolution model data shows that in large part of a cloud, the assumption of adiabaticity does not hold, which results in a similar bias in the LWP-CDNC (cloud droplet number concentration) relationship as seen in satellite data. In addition, our analysis shows a significant positive bias of between 18 % and 40 % in satellite-derived cloud droplet number concentration. However, for the individual ensemble members, the correlation between the cloud condensation nuclei and the mean of the liquid water path was very similar between the methods. This suggests that if cloud cases are carefully chosen for similar meteorological conditions and it is ensured that cloud condensation nuclei concentrations are well-defined, changes in liquid water can be confidently determined using satellite data.
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Journal articleKrämer E, Koller F, Suni J, et al., 2025,
Jets Downstream of Collisionless Shocks: Recent Discoveries and Challenges
, Space Science Reviews, Vol: 221, ISSN: 0038-6308Plasma flows with enhanced dynamic pressure, known as magnetosheath jets, are often found downstream of collisionless shocks. As they propagate through the magnetosheath, they interact with the surrounding plasma, shaping its properties, and potentially becoming geoeffective upon reaching the magnetopause. In recent years (since 2016), new research has produced vital results that have significantly enhanced our understanding on many aspects of jets. In this review, we summarise and discuss these findings. Spacecraft and ground-based observations, as well as global and local simulations, have contributed greatly to our understanding of the causes and effects of magnetosheath jets. First, we discuss recent findings on jet occurrence and formation, including in other planetary environments. New insights into jet properties and evolution are then examined using observations and simulations. Finally, we review the impact of jets upon interaction with the magnetopause and subsequent consequences for the magnetosphere-ionosphere system. We conclude with an outlook and assessment on future challenges. This includes an overview on future space missions that may prove crucial in tackling the outstanding open questions on jets in the terrestrial magnetosheath as well as other planetary and shock environments.
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Journal articleChitta LP, Huang Z, D'Amicis R, et al., 2025,
Coronal hole picoflare jets are progenitors of both fast and Alfvénic slow solar wind
, Astronomy and Astrophysics, Vol: 694, ISSN: 0004-6361Solar wind, classified by its bulk speed and the Alfvénic nature of its fluctuations, generates the heliosphere. The elusive physical processes responsible for the generation of the different types of this wind are a topic of active debate. Recent observations reveal intermittent jets, with kinetic energy in the picoflare range, emerging from dark areas of a polar coronal hole threaded by open magnetic field lines. These could substantially contribute to solar wind. However, their ubiquity and direct links to solar wind have not been established. Here, we report a unique set of remote-sensing and in situ observations from the Solar Orbiter spacecraft that establish a unified picture of fast and Alfvénic slow wind, connected to the similar widespread picoflare jet activity in two coronal holes. Radial expansion of coronal holes ultimately regulates the speed of the emerging wind.
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Journal articleWahlund J-E, Bergman JES, Ahlen L, et al., 2025,
The Radio & Plasma Wave Investigation (RPWI) for the JUpiter ICy moons Explorer (JUICE)
, Space Science Reviews, Vol: 221, ISSN: 0038-6308The Radio & Plasma Wave Investigation (RPWI) onboard the ESA JUpiter ICy moons Explorer (JUICE) is described in detail. The RPWI provides an elaborate set of state-of-the-art electromagnetic fields and cold plasma instrumentation, including active sounding with the mutual impedance and Langmuir probe sweep techniques, where several different types of sensors will sample the thermal plasma properties, including electron and ion densities, electron temperature, plasma drift speed, the near DC electric fields, and electric and magnetic signals from various types of phenomena, e.g., radio and plasma waves, electrostatic acceleration structures, induction fields etc. A full wave vector, waveform, polarization, and Poynting flux determination will be achieved. RPWI will enable characterization of the Jovian radio emissions (including goniopolarimetry) up to 45 MHz, has the capability to carry out passive radio sounding of the ionospheric densities of icy moons and employ passive sub-surface radar measurements of the icy crust of these moons. RPWI can also detect micrometeorite impacts, estimate dust charging, monitor the spacecraft potential as well as the integrated EUV flux. The sensors consist of four 10 cm diameter Langmuir probes each mounted on the tip of 3 m long booms, a triaxial search coil magnetometer and a triaxial radio antenna system both mounted on the 10.6 m long MAG boom, each with radiation resistant pre-amplifiers near the sensors. There are three receiver boards, two Digital Processing Units (DPU) and two Low Voltage Power Supply (LVPS) boards in a box within a radiation vault at the centre of the JUICE spacecraft. Together, the integrated RPWI system can carry out an ambitious planetary science investigation in and around the Galilean icy moons and the Jovian space environment. Some of the most important science objectives and instrument capabilities are described here. RPWI focuses, apart from cold plasma studies, on the understanding of how, thr
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Journal articleFlegrová M, Brindley H, 2025,
Two Decades of Fire-Induced Albedo Change and Associated Short-Wave Radiative Effect Over Sub-Saharan Africa
, Journal of Geophysical Research: Atmospheres, Vol: 130, ISSN: 2169-897XWe present an analysis of 20 years of fire and albedo data in Africa. We show that, in the mean, the sub-Saharan Africa post-fire surface albedo anomaly can be parameterized using an exponential recovery function, recovering from a decrease of (Formula presented.) immediately after a fire with a time constant of (Formula presented.) days. Although the magnitude of albedo changes shows large spatial and temporal variations and a strong land cover type (LCT) dependency, exponential recovery is observed in the majority of LCTs. We show that fires cause long-term surface brightening, with an Africa-wide albedo increase of (Formula presented.) 10 months after a fire, but we find this is driven almost exclusively by slow vegetation recovery in the Kalahari region, confirming previous findings. Using downward surface shortwave flux (DSSF) estimates, we calculate the fire-induced surface radiative forcing (RF), peaking at (Formula presented.) Wm−2 in the burn areas, albeit with a significantly smaller effect when averaged temporally and spatially. We find that the long-term RF in months 5–10 after a burn averaged over the continent is negative because of the brightening observed. Despite a well-documented reduction in burning in Africa in the recent decades, our temporal analysis does not indicate a decrease in the overall fire-induced RF likely due to large interannual variability in albedo anomaly and DSSF data. However, we observe a decline in the short-term RF in southern hemisphere Africa, driven by both a reduction in fires and changes in LCT distributions.
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Conference paperMurray-Watson R, Gryspeerdt E, 2025,
Air mass history linked to the development of Arctic mixed-phase clouds
<jats:p>The development of clouds during marine cold-air outbreaks (MCAOs) represent a complex phenomenon, transitioning from stratocumulus decks near ice edges to cumuliform fields downwind. This change cloud morphology changes the radiative properties of the cloud, and therefore is of importance to the surface energy budget. Therefore, it is crucial to understand the factors which may drive transition to a broken cloud field. Previous in situ and modelling studies suggest the formation of ice may enhance precipitation and therefore accelerate break-up. However, little is known about the development of mixed-phase clouds in MCAOs.&#160;This study uses pseudo-Lagrangian trajectories and satellite data to analyze this mixed-phase cloud development. We observe a rapid transition from liquid to ice phases in MCAO clouds, contrasting with similar cloud formations outside MCAO conditions. These mixed-phase clouds initially form at temperatures below -20&#176;C near ice edges but can dominate even at -13&#176;C further into outbreaks. This temperature shift suggests a significant role for biological ice nucleating particles (INPs), which increase in prevalence as air masses age over marine environments. The study also notes the influence of the air mass's history over snow- and ice-covered surfaces, which may be low in INPs, on cloud evolution. This link helps explain seasonal variations in Arctic cloud development, both during and outside of MCAOs. Our findings emphasize the importance of understanding local marine aerosol sources and the broader INP distribution in the Arctic for accurate cloud phase modeling in the region.&#160;</jats:p>
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Journal articleBeth A, Galand M, Modolo R, et al., 2025,
Ionospheric environment of Ganymede during the Galileo flybys
<jats:p>The Galileo spacecraft flew by Ganymede, down to 0.1 RG from the surface for the closest, six times giving us insight into its plasma environment. Its ionosphere, made of ions born from the ionisation of neutrals present in Ganymede&#8217;s exosphere, represents the bulk of the plasma near the moon around closest approach. As it has been revealed by Galileo and Juno, near closest approach the ion population is dominated by low-energy ions from the water ion group (O+, HO+, H2O+) and O2+. However, little is known about their density, spatial distribution, and effect on the surface weathering of the moon itself. Galileo G2 flyby has been extensively studied. Based on a comparison between observations and 3D test-particle simulations, Carnielli et al. (2020a and 2020b) confirmed the ion composition (debated at the time), highlighted the inconsistency between the assumed exospheric densities and the observed ionospheric densities, and derived the contribution of ionospheric ions as an exospheric source. However, other flybys of Ganymede are also available (e.g. G1, G7, G8, G28, and G29) providing in-situ measurements at different phases of Ganymede around Jupiter or jovian magnetospheric conditions at the moon. We extend the original study by Carnielli et al. to other flybys, and compare our modelled ion moments (ion number density, velocity, and energy distribution) with Galileo in-situ data. We discuss our results and contrast them with those obtained for the G2 flyby.&#160;&#160;</jats:p>
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Conference paperLewis Z, Beth A, Galand M, et al., 2025,
Constraining ion transport in the diamagnetic cavity of comet 67P
<jats:p>Comets are small icy bodies originating from the outer solar system that produce an increasingly dense gas coma through sublimation as they approach perihelion. Photoionisation of this gas results in a cometary ionosphere, which interacts with the impinging solar wind, leading to large scale plasma structures. One such structure is the diamagnetic cavity: the magnetic field-free inner region that the solar wind cannot penetrate. This region was encountered many times by the ESA Rosetta mission, which escorted comet 67P/Churyumov-Gerasimenko for a two-year section of its orbit.Within the diamagnetic cavity, high ion bulk velocities have been observed by the Rosetta Plasma Consortium (RPC) instruments. The fast ions are thought to have been accelerated by an ambipolar electric field, but the nature and strength of this field are difficult to determine analytically. Our study therefore aims to model the impact of various electric field profiles on the ionospheric density profile and ion composition. The 1D numerical model we have developed includes three key ion species (H2O+, H3O+, and NH4+) in order to assess the sensitivity of each to the timescale of plasma loss through transport. NH4+ is of particular interest, as it has been previously shown to be the dominant ion species at low cometocentric distances near perihelion. It is only produced through the protonation of NH3, a minor component of the neutral gas, and we show that this makes it particularly sensitive to the electric field.We also compare the simulated electron density to RPC datasets, to find the electric field strength and profile which best recreate the plasma densities measured inside the diamagnetic cavity near perihelion. From this, we also constrain the radial bulk ion speed that is required to explain the observations with the model.</jats:p>
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Journal articleKaweeyanun N, Masters A, 2025,
Three-dimensional modelling of Ganymede’s Chapman–Ferraro magnetic field and its role in subsurface ocean induction
, Icarus, Vol: 426, ISSN: 0019-1035In April 2023, the Jupiter Icy Moons Explorer (Juice) began its journey to orbit Jupiter’s largest and only magnetic moon, Ganymede. Part of the mission’s objectives aim to verify existence of the moon’s subsurface ocean and determine its structure through its induced response to external excitation by periodically varying magnetic field. Known contributions to the excitation are those from Jupiter’s dipole (at synodic period) and quadrupole (at half-synodic period) variations, and Ganymede’s inclined eccentric orbit around Jupiter (at orbital period). We propose that Ganymede’s magnetopause, where the Chapman–Ferraro (C–F) magnetic field arises from local currents, also contributes to subsurface ocean induction. This article introduces the first three-dimensional model of the C–F field and its outputs at Ganymede’s subsurface ocean and larger magnetosphere. The field is shown to be non-uniform — strongest near upstream Ganymede’s subflow region and gradually weakening away from it. Magnetopause asymmetry due to the Jovian guide field results in largely synodic variation of the C–F field, with exceptions near Ganymede’s equator and subflow meridian where asymmetry effects are minimal and the variations are half-synodic. The C–F field amplitude is of general order ∼50 nT, which is significant relative to excitation from the Jovian field. Comparisons to Galileo data and magnetohydrodynamic simulation results suggest the model is useful, therefore the magnetopause effects must be considered in future induction modeling of Ganymede’s subsurface ocean ahead of the Juice mission.
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Journal articleWang JH, Horbury TS, Matteini L, et al., 2025,
Alpha–proton relative drift: implications for the origins and dynamics of the solar wind
, Letters of the Astrophysical Journal, Vol: 978, ISSN: 2041-8205Helium nuclei (alpha particles) strongly influence the momentum and energy balance in the solar wind, comprising up to 20% of the solar wind mass density. In fast Alfvénic wind at heliocentric distances greater than 0.3 au, the alpha particles' bulk flow speed is systematically different to that of the protons. This relative drift speed is of unknown origin and is often close to the local Alfvén wave speed. Novel Parker Solar Probe measurements of the solar wind below 0.3 au show that, closer to the Sun, the alpha–proton drift speed remains on the order of 100–200 km s−1, even where the Alfvén speed is greater than 600 km s−1. This relative speed is quantitatively similar to oxygen–hydrogen drift speeds observed in the transition region by remote sensing, suggesting similar selective acceleration processes in the corona. Due to the relative speed of the Alfvén wave to each particle population close to the Sun, the alphas fluctuate with velocity amplitudes comparable to those of the protons, altering the energy balance of the wave. As a result, alpha particles carry a significant fraction of the total kinetic energy in Alfvénic fluctuations in the near-Sun solar wind. The alpha–proton drift speed is comparable to the proton speed in the near-Sun wind, making the bulk flow of the alpha particles a significant contribution to the kinetic energy flux. These heavy-ion dynamics provide new observational constraints on quantifying the energy budget of the solar wind and the magnetic field evolution through the heliosphere.
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Journal articleLow J, Teoh R, Ponsonby J, et al., 2025,
Ground-based contrail observations: Comparisons with reanalysis weather data and contrail model simulations
, Atmospheric Measurement Techniques, Vol: 18, Pages: 37-56, ISSN: 1867-1381Observations of contrails are vital for improving our understanding of the contrail formation and life cycle, informing models, and assessing mitigation strategies. Here, we developed a methodology that utilises ground-based cameras for tracking and analysing young contrails (< 35 min) formed under clear-sky conditions, comparing these observations against reanalysis meteorology and simulations from the contrail cirrus prediction model (CoCiP) with actual flight trajectories. Our observations consist of 14 h of video footage recorded over 5 different days in Central London, capturing 1582 flight waypoints from 281 flights. The simulation correctly predicted contrail formation and absence for around 75 % of these waypoints, with incorrect contrail predictions occurring at warmer temperatures than those with true-positive predictions (7.8 K vs. 12.8 K below the Schmidt-Appleman criterion threshold temperature). When evaluating contrails with observed lifetimes of at least 2 min, the simulation's correct prediction rate for contrail formation increases to over 85 %. Among all waypoints with contrail observations, 78 % of short-lived contrails (observed lifetimes < 2 min) formed under ice-subsaturated conditions, whereas 75 % of persistent contrails (observed lifetimes > 10 min) formed under ice-supersaturated conditions. On average, the simulated contrail geometric width was around 100 m smaller than the observed (visible) width over its observed lifetime, with the mean underestimation reaching up to 280 m within the first 5 min. Discrepancies between the observed and simulated contrail formation, lifetime, and width can be associated with uncertainties in reanalysis meteorology due to known model limitations and sub-grid-scale variabilities, contrail model simplifications, uncertainties in aircraft performance estimates, and observational challenges, among other possible factors. Overall, this study demonstrates the potential of ground-based cameras to create
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