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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 articleSeo GY, Min SK, Lee D, et al., 2025,
Hourly extreme rainfall projections over South Korea using convection permitting climate simulations
, Npj Climate and Atmospheric Science, Vol: 8This study analyzes the impact of climate change on the summertime hourly extreme rainfall event (HER) over South Korea. The UKESM-forced regional climate model is utilized to simulate HER over South Korea in the historical (2001–2005) and future periods (2091–2095) under the SSP1-2.6 and SSP5-8.5 scenarios at a convection-permitting resolution (2.5 km). A significant increase in future HER intensity and frequency appears in July, with the frequency increases about two times for SSP1-2.6 and about 3.7 times for SSP5-8.5 scenarios. The month of maximum HER frequency is also projected to shift from August to July. When clustering the HERs into six representative weather patterns, SSP5-8.5 scenarios show a predominant increase in weather patterns characterized by a frontal boundary between low and high pressure in July. Our results suggest that the future sub-seasonal evolution of HER over South Korea may change with the intensification of subtropical high and the deepening of mid-level trough according to different future scenarios.
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Journal articleWilson LB, Mitchell JG, Szabo A, et al., 2025,
Large-amplitude Whistler Precursors and >MeV Particles Observed at a Weak Interplanetary Shock by Parker Solar Probe
, Astrophysical Journal, Vol: 987, ISSN: 0004-637XWe report observations of an interplanetary (IP) shock observed by Parker Solar Probe (PSP) on 2024 September 29 at ∼07:50:29 UTC. PSP was only ∼17.07 R<inf>s</inf> from the Sun, making this one of the closest observed IP shocks to date. The IP shock was a weak (M<inf>f</inf> ∼ 1.2), quasi-perpendicular (θ<inf>Bn</inf> ∼ 50°), and of moderate speed (V<inf>shn</inf> ∼ 465 km s<sup>−1</sup>). The standard shock acceleration mechanisms (e.g., Fermi acceleration) predict that such an unremarkable shock cannot generate energetic particles (i.e., over 4 orders of magnitude above thermal energies), which is supported by decades of IP shock observations near 1 au. However, ∼MeV energy protons with an inverse velocity arrival and synchrotron radiation (due to ∼MeV energy electrons) were observed upstream. This raised the question of what was different about this shock. One observation was that of a fast/magnetosonic-whistler precursor with peak-to-peak magnetic field amplitudes >700 nT, electric fields >2000 mV m<sup>−1</sup>, and Poynting fluxes >230 mW m<sup>−2</sup>. These are 2 orders of magnitude larger than any previously observed whistler precursor. To put the amplitudes in context, the lower bound Poynting flux estimates are >200 times what is necessary to drive the terrestrial aurora. Note that the normalized wave parameters (e.g., frequency) were found to be consistent with previous studies near 1 au. Thus, the precursors cannot likely generate a larger fraction of energetic particles than similar precursors near 1 au. However, the much larger amplitudes would allow for higher maximum energies. This raises important questions about inaccessible shocks in more extreme astrophysical environments and what potential energization they may have in light of these observations.
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Journal articleRen T, Yang P, Brindley HE, et al., 2025,
Temperature-Dependent Optical Properties of Ice Crystals in the Far-Infrared Regime
, Geophysical Research Letters, Vol: 52, ISSN: 0094-8276A database of temperature-dependent hexagonal ice aggregate optical properties in the far-infrared (FIR) spectrum is developed to support FIR missions, particularly the current Polar Radiant Energy in the Far InfraRed Experiment and the upcoming Far-infrared-Outgoing-Radiation Understanding and Monitoring. Based on this data set, simulations of the brightness temperatures (BTs) in the 100–667 cm<sup>−1</sup> FIR region are conducted for an anvil-like ice cloud in a tropical atmosphere. The results show nonnegligible impact of ice cloud temperature on simulated BTs, which can be as large as 3 K due to the difference between fixed 160 or 270 K cloud temperature and the benchmark counterpart, varying in accordance with the ambient temperature profile for a cloud residing between 249.6 and 199.6 K. To enhance the accuracy of FIR radiative transfer modeling, it is recommended to incorporate temperature-dependent optical properties of ice clouds.
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Journal articleGoodwin P, Williams RG, Ceppi P, et al., 2025,
Climate Feedbacks Derived From Spatial Gradients in Recent Climatology
, Journal of Geophysical Research Atmospheres, Vol: 130, ISSN: 2169-897XClimate feedbacks, including Planck, surface albedo, water vapor-lapse rate (WVLR) and cloud feedbacks, determine how much surface temperatures will eventually warm to balance anthropogenic radiative forcing. Climate feedbacks remain difficult to constrain directly from temporal variation in observed surface warming and radiation budgets due to the pattern effect and low signal-to-noise ratio, with only order 1°C historic rise in surface temperatures and high uncertainty in aerosol radiative forcing. This study presents a new method to analyze climate feedbacks from observations by empirically fitting simplified reduced-physics relations for outgoing radiation at the top of the atmosphere (TOA) to observed spatial variation in climate properties and radiation budgets. Spatial variations in TOA outgoing radiation are dominated by the dependence on surface temperature: around 91% of the spatial variation in clear sky albedo, and 77% of spatial variation in clear sky TOA outgoing longwave radiation, is functionally explained by variation in surface temperatures. These simplified and observationally constrained relations are then differentiated with respect to spatial contrasts in surface temperature to reveal the Planck, fixed-cloud albedo ((Formula presented.)) and WVLR ((Formula presented.)) climate feedbacks spatially for both clear sky and all sky conditions. The resulting global all sky climate feedback values are (Formula presented.) = 1.28 (1.13–1.45 at 66%) Wm<sup>−2</sup>K<sup>−1</sup>, and (Formula presented.) = 0.64 (0.53–0.74) Wm<sup>−2</sup> for the period 2003–2023, reducing to 0.35 (0.29–0.41) Wm<sup>−2</sup>K<sup>−1</sup> under 4°C warming after cryosphere retreat. Our findings agree well with complex Earth system model evaluations based on temporal climate perturbations, and our approach is complementary.
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Journal articleTurc L, Archer MO, Zhou H, et al., 2025,
Interplay between a foreshock bubble and a hot flow anomaly forming along the same rotational discontinuity
, Geophysical Research Letters, Vol: 52, ISSN: 0094-8276Solar wind directional discontinuities can generate transient mesoscale structures such as foreshock bubbles and hot flow anomalies (HFAs) upstream of Earth's bow shock. These structures can have a global impact on near-Earth space, so understanding their formation conditions is essential. We investigate foreshock transient generation at a rotational discontinuity using a global 2D hybrid-Vlasov simulation. As expected, a foreshock bubble forms on the sunward side of the discontinuity. Later, when the discontinuity reaches the shock, new structures identified as HFAs develop, despite the initial discontinuity not being favorable to HFA formation. We demonstrate that the foreshock bubble provides the necessary conditions for their generation. We then investigate the evolution of the transient structures and the large-scale bow shock deformation they induce. Our results provide new insights on the formation and evolution of foreshock transients and their impact on the shock.
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Journal articleHuang J, Larson DE, Ervin T, et al., 2025,
The Temperature Anisotropy and Helium Abundance Features of Alfvénic Slow Solar Wind Observed by Parker Solar Probe, Helios, and Wind Missions
, Astrophysical Journal Letters, Vol: 986, ISSN: 2041-8205Slow solar wind is typically characterized as having low Alfvénicity, but the occasional occurrence of highly Alfvénic slow solar wind (HASSW) raises questions about its source regions and evolution. In this work, we conduct a statistical analysis of temperature anisotropy and helium abundance in HASSW using data from the Parker Solar Probe (PSP) within 0.25 au, Helios between 0.3 au and 1 au, and Wind near 1 au. Our findings reveal that HASSW is prevalent close to the Sun, with PSP observations displaying a distinct “U-shaped” Alfvénicity distribution with respect to increasing solar wind speed, unlike the monotonic increase trend seen in Helios and Wind data. This highlights a previously unreported population of unusually low-speed HASSW, which is found in both sub-Alfvénic and super-Alfvénic regimes. The observed decreasing overlap in temperature anisotropy between HASSW and fast solar wind (FSW) with increasing heliocentric distance suggests different underlying heating processes. Additionally, HASSW exhibits two distinct helium abundance populations, particularly evident in PSP data, with generally higher helium abundance compared to less Alfvénic slow solar wind. Moreover, the decreasing overlap in temperature anisotropy versus helium abundance distributions between HASSW and FSW with decreasing radial distance implies that not all HASSW originates from the same source region as FSW.
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Journal articlePhan TD, Romeo OM, Drake JF, et al., 2025,
Parker Solar Probe Observations of a Highly Energetic and Asymmetric Reconnecting Heliospheric Current Sheet during Encounter 13
, Astrophysical Journal, Vol: 986, ISSN: 0004-637XWe report Parker Solar Probe observations of reconnection during an unusual heliospheric current sheet (HCS) crossing at 14.8 solar radii that occurred ∼15 hr after the passage of a CME. The HCS was surrounded by unusually low solar wind density. The hybrid Alfvén speed (V<inf>A</inf> ∼ 515 km s<sup>−1</sup>) and available magnetic energy per particle (m<inf>i</inf>V<inf>A</inf><sup>2</sup> ∼ 3 keV) were the highest observed to date surrounding an HCS. Inside the HCS, the peak outflow speed (∼525 km s<sup>−1</sup>) and proton and electron bulk heating, at ∼400 eV and ∼25 eV, respectively, were also the highest observed to date associated with HCS reconnection. Unusual for an HCS, the density on the two sides of the HCS differed by a factor of ∼13. Consequently, the spatial plasma profiles across the HCS resembled those of planetary magnetopauses, with the fastest outflow occurring near the low-density edge of the HCS. A striking feature of this HCS is the asymmetric nature of the superthermal protons escaping the HCS along separatrix field lines. On the low solar wind density side, the low-velocity cutoff of escaping protons was substantially higher than on the high-density side. The cutoffs were close to the bulk outflow speeds measured near the two edges of the asymmetric HCS, suggesting that only particles faster than the outflow speeds can escape the HCS. Electrons were also energized and leaked out of the HCS, forming a layer of field-aligned superthermal electrons. These escaping electrons are distinguishable from solar strahl electrons observed further away from the HCS, which had lower energies.
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Journal articleDakeyo JB, Démoulin P, Rouillard A, et al., 2025,
Generalized Two Thermal Regime Approach: Bipoly Fluid Modeling
, Astrophysical Journal, Vol: 986, ISSN: 0004-637XThe isopoly bifluid approach assumes an isothermal evolution of the solar wind near the Sun up to the radial distance r<inf>iso</inf>, followed by a polytropic evolution constrained by the observed polytropic indices. This approach provides a more accurate model of the interplanetary fluid properties of the solar wind and their radial evolution than Parker’s isothermal and polytropic wind. In this article, we present an improvement of the isopoly approach by considering a generalized two thermal regime approach, embedding two distinct polytropic evolutions, the “bipoly” modeling. To demonstrate the capability of the approach, the models are fitted to both interplanetary and coronal observations, all classified by wind speed population in the spirit of M. Maksimovic et al. The set of observations used as constraints are coronal temperatures inferred from charge-state ratio observations from Solar Orbiter, and interplanetary measurements from Helios and Parker Solar Probe. The relaxation of the isothermal criteria in the near-Sun region permits one to significantly improve the fast wind acceleration for low-coronal-temperature conditions. In summary, the new model matches closely the observational constraints: the coronal temperature and the radial evolution of the wind plasma properties in the interplanetary medium, and this for all the wind speed populations.
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Journal articleGrillakis M, Voulgarakis A, 2025,
Diverse wildfire impacts on river flows across the globe
, Communications Earth & Environment, Vol: 6, ISSN: 2662-4435Forest fires can significantly impact the hydrological regime of river basins, affecting short-term flood propensity and long-term water resource availability until vegetation is reestablished. While basin-level studies have extensively investigated these impacts, regional and global-scale assessments remain limited. Here we use a comprehensive global dataset of river discharge observations to systematically assess the hydrological response to wildfires for a range of hydrologically homogenous world regions and biomes. Our analysis reveals contrasting hydrological impacts by region, with high-latitude discharge ratios declining by 7.5% and 16% in the first and second year after wildfire, respectively, while Northern mid-latitude regions showing a marginal 3.3% median increase in discharge ratio the first-year post-fire. Sub-tropical and equatorial regions display negative and positive effects, respectively. We further discuss how potential ecological and hydroclimatic factors, along with human river and watershed management, shape these diverse hydrological responses per hydroclimatic region.
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Journal articleZomerdijk-Russell S, Jasinski J, Masters A, 2025,
Variation of model-predicted reconnection voltages applied to Uranus’ dayside magnetosphere
, JGR: Space Physics, ISSN: 2169-9402Uranus provides a key missing piece for fundamentally understanding solar wind-magnetospheric interactions due to its location in the outer solar system. Whether the viscous-like interaction overtakes global magnetic reconnection as the dominant process at the magnetopauseof the outer planets remains unresolved. Here, we present theoretical predictions of dayside reconnection voltages applied to the Uranian system under different magnetospheric configurations to assess the effectiveness of global magnetic reconnection in the driving of Uranus’magnetosphere. We find the median model-predicted dayside reconnection voltage applied to Uranus’ magnetosphere is 22.4 kV. Over just one full planetary rotation, the reconnection voltages are found to vary by tens of kV under Uranus’ magnetospheric configuration during its solstice and equinox seasons with fixed solar wind conditions. However, we do not find a significant difference between average voltages at the different seasons, despite the large differences in magnetospheric configuration between solstice and equinox at Uranus. An increase from ~17 kV to ~31 kV in the modeled reconnection voltages is observed when the strength of the interplanetarymagnetic field is increased corresponding to expected conditions during solar maximum. Our results suggest that variability resulting from the planet’s diurnal rotation and changing solar wind conditions, are more important in controlling the reconnection voltages than seasonaldependencies.
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Journal articleHamilton CW, McEwen AS, Keszthelyi L, et al., 2025,
Comparing NASA Discovery and New Frontiers Class Mission Concepts for the Io Volcano Observer
, Planetary Science Journal, Vol: 6Jupiter’s moon Io is a highly compelling target for future exploration that offers critical insight into tidal dissipation processes and the geology of high heat flux worlds, including primitive planetary bodies, such as the early Earth, that are shaped by enhanced rates of volcanism. Io is important for understanding the development of volcanogenic atmospheres and mass exchange within the Jupiter system. However, fundamental questions remain about the state of Io’s interior, surface, and atmosphere, as well as its role in the evolution of the Galilean satellites. The Io Volcano Observer (IVO) would advance answers to these questions by addressing three key goals: (A) determine how and where tidal heat is generated inside Io, (B) understand how tidal heat is transported to the surface of Io, and (C) understand how Io is evolving. IVO was selected for Phase A study through the NASA Discovery program in 2020, and, in anticipation of the next New Frontiers (NF) opportunity, an enhanced IVO-NF mission concept would increase the Baseline mission from 10 flybys to 20, with an improved radiation design; employ a Ka-band communication system to double IVO’s total data downlink; add a wide-angle camera for color and stereo mapping; add a dust mass spectrometer; and lower the altitude of later flybys to enable new science. This study compares the architecture, instrument suite, and science objectives for Discovery (IVO) and NF (IVO-NF) missions to Io. IVO can achieve outstanding science results at the Discovery level, but we advocate for continued prioritization of Io for NF.
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Journal articleLozinski AR, Kellerman AC, Bortnik J, et al., 2025,
Modeling the Internal Redistribution of Earth's Proton Radiation Belt by Interplanetary Shocks
, Journal of Geophysical Research Space Physics, Vol: 130, ISSN: 2169-9380A large proton belt enhancement occurred on 24 March 1991 following an interplanetary shock that impacted the dayside magnetopause at (Formula presented.) 03:40 UT. Its formation was measured by the proton telescope aboard CRRES and attributed to the injection and inward transport of solar energetic particles (SEPs) by an azimuthally propagating electric field pulse induced by the shock's compression of the magnetosphere. This led to an increase in the flux of high energy ((Formula presented.) 25 MeV) protons by several orders of magnitude at (Formula presented.) which has been well-studied. However, a flux enhancement by up to one order of magnitude was also seen in 1–20 MeV protons at (Formula presented.). Protons in this energy range pose a hazard to orbiting spacecraft as a major contributor to solar cell nonionizing dose. The 1–20 MeV enhancement cannot be explained by the inward transport of a solar proton source, because a newly injected source population at the required energy would have a drift velocity too low to interact with the pulse. Instead, we hypothesize that the 1–20 MeV enhancement was caused by the redistribution of radiation belt protons to different drift shells by the pulse. To test this hypothesis, we apply a novel method to predict the change in phase space density during a shock event which utilizes reverse-time particle tracing simulations. Our results show that the 1–20 MeV enhancement can be accounted for by internal redistribution as hypothesized. We thus identify a new mechanism for proton belt enhancements that does not depend on a SEP source and present a way to model it.
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Journal articleMauritsen T, Tsushima Y, Meyssignac B, et al., 2025,
Earth's Energy Imbalance More Than Doubled in Recent Decades
, Agu Advances, Vol: 6Global warming results from anthropogenic greenhouse gas emissions which upset the delicate balance between the incoming sunlight, and the reflected and emitted radiation from Earth. The imbalance leads to energy accumulation in the atmosphere, oceans and land, and melting of the cryosphere, resulting in increasing temperatures, rising sea levels, and more extreme weather around the globe. Despite the fundamental role of the energy imbalance in regulating the climate system, as known to humanity for more than two centuries, our capacity to observe it is rapidly deteriorating as satellites are being decommissioned.
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Journal articleHorner G, Gryspeerdt E, 2025,
How does the lifetime of detrained cirrus impact the high-cloud radiative effect in the tropics?
, Atmospheric Chemistry and Physics, Vol: 25, Pages: 5617-5631, ISSN: 1680-7316The lifetime of cirrus clouds from deep convection plays an important role in determining their overall cloud radiative effect (CRE). The net CRE of cirrus clouds from deep convection is close to zero over their whole lifetime. This CRE is the result of a near-cancellation of a large shortwave (SW) cooling and large longwave (LW) warming, such that small changes in cirrus properties have the potential to produce a significant net radiative effect. Changes in the atmospheric and sea surface temperature structure, along with changes in anthropogenic aerosol, have been hypothesised to impact the lifetime of detrained cirrus clouds, altering this radiative balance. Constraining the potential CRE response to changes in cirrus lifetime is therefore vital to understand the strength of these proposed climate forcings and feedbacks.This paper tracks the evolution of detrained cirrus clouds along trajectories from deep convection. The total cirrus CRE in the tropics is found to be warming, at 11.2 ± 0.4 W m−2. It is found that cirrus clouds along trajectories from oceanic origin convection have a warming CRE of 10.0 ± 0.4 W m−2. In contrast, cirrus clouds along trajectories from land convection have a warming of 15.9 ± 0.7 W m−2 throughout their lifetime. This contrast is predominantly due to differences in the diurnal cycle of the initial convection over land and ocean.A proposed extension to the lifetime of the detrained cirrus leads to changes in the total cirrus CRE in the tropics. In all cases, doubling the lifetime of the detrained cirrus leads to an increase in the total cirrus CRE of 0.6 ± 0.1 W m−2. Whilst there is uncertainty in the strength of mechanisms responsible for a change in cirrus lifetime, this work provides an important constraint on the impact that any potential lifetime extension may have.
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Journal articleDesai MI, Drake JF, Phan T, et al., 2025,
Magnetic Reconnection-driven Energization of Protons up to ∼400 keV at the Near-Sun Heliospheric Current Sheet
, Astrophysical Journal Letters, Vol: 985, ISSN: 2041-8205We report observations of direct evidence of energetic protons being accelerated above ∼400 keV within the reconnection exhaust of a heliospheric current sheet (HCS) crossing by NASA’s Parker Solar Probe (PSP) at a distance of ∼16.25 solar radii (R<inf>s</inf>) from the Sun. Inside the exhaust, both the reconnection-generated plasma jet and the accelerated protons up to ∼400 keV propagated toward the Sun, unambiguously establishing their origin from HCS reconnection sites located antisunward of PSP. Within the core of the exhaust, PSP detected stably trapped energetic protons up to ∼400 keV, which is ≈1000 times greater than the available magnetic energy per particle. The differential energy spectrum of the accelerated protons behaved as a pure power law with spectral index of ∼−5. Supporting simulations using the kglobal model suggest that the trapping and acceleration of protons up to ∼400 keV in the reconnection exhaust are likely facilitated by merging magnetic islands with a guide field between ∼0.2 and 0.3 of the reconnecting magnetic field, consistent with the observations. These new results, enabled by PSP’s proximity to the Sun, demonstrate that magnetic reconnection in the HCS is a significant new source of energetic particles in the near-Sun solar wind. Our findings of in situ particle acceleration via magnetic reconnection at the HCS provide valuable insights into this fundamental process, which frequently converts the large magnetic field energy density in the near-Sun plasma environment and may be responsible for heating the Sun’s atmosphere, accelerating the solar wind, and energizing charged particles to extremely high energies in solar flares.
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Journal articleKim K, Edberg NJT, Modolo R, et al., 2025,
Electron Structures in Titan's Induced Magnetosphere and Low-Frequency Wave Activity
, Journal of Geophysical Research Planets, Vol: 130, ISSN: 2169-9097The interaction of Titan's ionosphere with Saturn's magnetosphere leads to a mix of perturbed electromagnetic fields and accelerated and thermalized plasma in the induced magnetosphere. The complexity of this region has been noted in previous studies. However, many local structures and processes have not been studied and addressed in detail before. In this case study, we examine the origin of quasi-periodic plasma structures in Titan's induced magnetosphere observed during the T36 flyby. We use data from the electron and ion spectrometers CAPS/ELS and IMS, the RPWS Langmuir probe and electric antenna, and the fluxgate magnetometer (MAG) to analyze plasma parameters, for example, density and temperature and magnetic field fluctuations, to characterize the processes involved. The observed plasma structures are quasi-periodic on a scale of about 20 s (or local ion gyroperiod) and possess acceleration signatures from a few eV up to 700 eV. A burst of low-frequency (around the ion-cyclotron and lower-hybrid frequency) and low-amplitude ((Formula presented.) nT, (Formula presented.) 0.14) waves are observed in the proximity of the plasma structures. We discuss possible mechanisms leading to the development of the observed plasma structures, for example, magnetohydrodynamics instabilities and the contribution of the local electric fields.
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Journal articleBowen TA, Dunn CI, Mallet A, et al., 2025,
Nonlinear Interactions in Spherically Polarized Alfvénic Turbulence
, Astrophysical Journal, Vol: 985, ISSN: 0004-637XTurbulent magnetic field fluctuations observed in the solar wind often maintain a constant-magnitude magnetic field accompanied by spherically polarized velocity fluctuations; these signatures are characteristic of large-amplitude Alfvén waves. Nonlinear energy transfer in Alfvénic turbulence is typically considered in the small-amplitude limit where the constant-magnitude condition may be neglected; in contrast, nonlinear energy transfer of large-amplitude fluctuations remains relatively unstudied. We develop a method to analyze large-amplitude turbulence through studying fluctuations as constant-magnitude rotations in the de Hoffmann-Teller frame, in which the convected electric field of the fluctuations vanishes such that the frame and fluctuations are copropagating. Our analysis reveals signatures of large-amplitude effects deep into the inertial range. While the dominant fluctuations are consistent with spherically polarized large-amplitude Alfvén waves, the subdominant fluctuations are relatively compressible. Signatures of nonlinear interaction between the large-amplitude spherically polarized mode with the subdominant population reveal highly aligned transverse components. In many theoretical models of Alfvénic turbulence, alignment is thought to reduce nonlinearity; our observations suggest that the observed alignment is sufficient to either reduce shear nonlinearity such that non-Alfvénic interactions may be responsible for energy transfer in spherically polarized states, or alternatively that counterpropagating fluctuations maintain anomalous coherence, a predicted signature of reflection-driven turbulence.
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Journal articleAlnussirat ST, Larson DE, Livi R, et al., 2025,
Impulsive Solar Flares in the Parker Solar Probe Era. I. Low-energy Electron, Proton, and Alpha Beams
, Astrophysical Journal, Vol: 985, ISSN: 0004-637XMultiple instruments on board the Parker Solar Probe spacecraft have detected signatures of impulsive electron and ion beam events over the course of the first 20 encounters. The energy spectra of these events are characterized by a peak originating in the low-frequency bandwidth of the FIELDS sensor and descending over time in energy until it merges with the bulk of the solar wind as observed by the Solar Wind Electrons, Alphas, and Protons suite. All events are well associated with Type III radio bursts, and some are well correlated with soft and hard X-rays generated by impulsive solar flares. These dispersive energy beam phenomena are essential in understanding particle acceleration, transport, and energy partitioning between electrons and ions as a result of impulsive solar flares. In this work, we present an analysis of said events and leverage multiwavelength observations that are conducted by instruments on multiple platforms. Our results show, for the first time, that solar flares are observed to be the source of low-energy ions in interplanetary space. This discovery has never been previously observed at such low energies by instruments at 1 au.
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Journal articleCuesta ME, Livadiotis G, McComas DJ, et al., 2025,
Transfer of Entropy between the Magnetic Field and Solar Energetic Particles during an Interplanetary Coronal Mass Ejection
, Astrophysical Journal Letters, Vol: 984, ISSN: 2041-8205The thermodynamics of solar wind bulk plasma have been routinely measured and quantified, unlike those of solar energetic particles (SEPs), whose thermodynamic properties have remained elusive until recently. The thermodynamic kappa (κ<inf>EP</inf>) that parameterizes the statistical distribution of SEP kinetic energy contains information regarding the population’s level of correlation and effective degrees of freedom (d<inf>eff</inf>). At the same time, the intermittent kappa (κ<inf>ΔB</inf>) that parameterizes the statistical distribution of magnetic field increments contains information about the correlation and d<inf>eff</inf> involved in magnetic field fluctuations. Correlations between particles can be affected by magnetic field fluctuations, leading to a relationship between κ<inf>EP</inf> and κ<inf>ΔB</inf>. In this Letter, we examine the relationship of d<inf>eff</inf> and entropy between energetic particles and the magnetic field via the spatial variation of their corresponding parameter kappa values. We compare directly the values of κ<inf>EP</inf> and κ<inf>ΔB</inf> using Parker Solar Probe IS⊙IS and FIELDS measurements during a SEP event associated with an interplanetary coronal mass ejection (ICME). Remarkably, we find that κ<inf>EP</inf> and κ<inf>ΔB</inf> are anticorrelated via a linear relationship throughout the passing of the ICME, indicating a proportional exchange of d<inf>eff</inf> from the magnetic field to energetic particles, i.e., κ<inf>ΔB</inf> ∼ (−0.15 ± 0.03)κ<inf>EP</inf>, interpreted as an effective coupling ratio. This finding is crucial for improving our understanding of ICMEs and suggests that they help to produce an environment that enables the transfer of
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Journal articleShen MM, Szalay JR, Pokorný P, et al., 2025,
Diverse Dust Populations in the Near-Sun Environment Characterized by PSP/ISʘIS
, Astrophysical Journal, Vol: 984, ISSN: 0004-637XThe Integrated Science Investigation of the Sun energetic particle instrument suite on the Parker Solar Probe is dedicated to measuring energetic ions and electrons in the near-Sun environment. It includes a half-sky-viewing time-of-flight mass spectrometer (EPI-Lo) and five high-energy silicon solid-state detector-telescopes (EPI-Hi). To 2024 August, eight of EPI-Lo’s eighty separate telescope foils have experienced direct dust puncture events, most of which occurred inside 40 solar radii (0.19 au). These impacts represent the closest high-fidelity dust detections to the Sun. While there is limited information about the size/mass of each impact due to the lack of a dedicated dust instrument, we can determine the impact direction for six punctures, allowing us to partially constrain abundant dust populations in the inner zodiacal cloud. Remarkably, one of six unambiguous dust impactors was likely on a retrograde orbit, suggesting long-period cometary material may survive within 20 solar radii (0.09 au). We discuss observations in the context of highlighting multiple dust populations responsible for these events to improve our understanding of the zodiacal dust environment in the inner heliosphere ( ≲ 1 au).
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Journal articleVallim D, Grillakis M, Manoudakis S, et al., 2025,
Stakeholder Engagement Drivers: Insights from an Information System Innovation Project Supporting Wildfire Evacuation in Greece
, Proceedings of the International Iscram ConferenceThe Samaria Gorge, a tourist destination in Crete, faces wildfire risk due to its dense forest, topography, number of visitors, and climate. As part of a H2020 project, the Gorge serves as a testing pilot for a new wildfire management platform that integrates technologies to improve fire detection, risk assessment, and resource allocation during a wildfire evacuation. A central component of the project is a multi-stakeholder network, which supports both governance and acceptance of solutions. To understand the drivers of network formation, we used a Social Network Analysis and Exponential Random Graphs Model approaches to identify the drivers of stakeholder collaboration. Our findings indicate that sectoral and wildfire management focus phase are factors driving connections, while the working in intersecting jurisdictions is not. The results highlight the challenges of multi-stakeholder collaboration, suggesting that policy frameworks and information systems need to develop specific mechanisms to encourage stakeholders to bridge collaborative gaps.
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Journal articleBeggan CD, Eastwood JP, Eggington JWB, et al., 2025,
Implementing an operational cloud‐based now‐ and forecasting system for space weather ground effects in the UK
, Space Weather, Vol: 23, ISSN: 1539-4956The enhanced variation of the magnetic field during severe to extreme geomagnetic storms induces a large geoelectric field in the subsurface. Grounded infrastructure can be susceptible to geomagnetically induced currents (GICs) during these events. Modeling the effect in real-time and forecasting the magnitude of GICs are important for allowing operators of critical infrastructure to make informed decisions on potential impacts. As part of the UK-funded Space Weather Innovation, Measurement, Modeling and Risk (SWIMMR) program, we implemented nine research-level models into operational codes capable of running consistently and robustly to produce estimates of GICs in the Great Britain high voltage power transmission network, the high pressure gas pipeline network and the railway network. To improve magnetic coverage and geoelectric field modeling accuracy, three new variometer sites were installed in the UK and a 3 year campaign of magnetotelluric measurements at 53 sites was undertaken. The models rely on real-time ground observatory data and solar wind data from satellites at the L1 Lagrange point. A mixture of empirical machine learning and numerical magnetohydrodynamic models are used for forecasting. In addition to nowcast capabilities, contextual information on the likelihood of substorms, sudden commencements and large rates of change of the magnetic field were developed. The final nowcast and forecast codes were implemented in a cloud-based environment using modern software tools and practices. We describe the process to move from research to operations (R2O).
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Journal articleNair R, Halekas JS, Cattell C, et al., 2025,
Suprathermal Electron Scattering by Narrowband Whistler Waves and Broadband Electrostatic Waves: Parker Solar Probe Observations
, Astrophysical Journal, Vol: 984, ISSN: 0004-637XWe utilize Parker Solar Probe measurements from the first nine perihelia to investigate suprathermal electron scattering near the Sun. We employ a normalized isotropy parameter to identify pitch-angle scattering (PAS) regions in the inner heliosphere, and compare the plasma conditions during these periods to the background (BG) solar wind. Suprathermal electron scattering also commonly occurs during full/partial current sheet (PCS) heliospheric current sheet (HCS) crossings, as identified in previous work. We find slightly higher electron collisional ages in the PAS and PCS/HCS regions than in BG regions, but conclude that Coulomb collisions alone likely cannot explain the observed suprathermal scattering. We investigate plasma wave-modes that could play a role in suprathermal electron scattering, and identify trends in the wave occurrence in BG, PAS, and PCS/HCS regions. We find higher occurrence rates of narrowband whistler-mode waves with frequencies of 0.04-0.19 f/f<inf>ce</inf>, and a higher occurrence of larger magnetic field wave power in this frequency band, in the PAS and PCS/HCS regions. These observations support the hypothesis that whistler-mode waves play a role in suprathermal electron scattering at moderate distances. However, closer to the Sun, narrowband whistlers are more rarely observed. Instead, we find higher occurrence rates of broadband electrostatic waves with frequencies of 0.1-4.4 f/f<inf>lh</inf>, and a higher occurrence of larger electric wave power in this band, in the near-Sun PAS and PCS/HCS regions. These observations suggest a role for broadband electrostatic waves in suprathermal electron scattering closer to the Sun.
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Journal articlePerkins O, Kasoar M, Voulgarakis A, et al., 2025,
The Spatial Distribution and Temporal Drivers of Changing Global Fire Regimes: A Coupled Socio-Ecological Modeling Approach
, Earth S Future, Vol: 13The limited capacity of fire-enabled vegetation models to represent human influences on fire regimes is a fundamental challenge in fire science. This limitation places a major constraint on our capacity to understand how vegetation fire may change under future scenarios of climate change and socio-economic development. Here, we address this challenge by presenting a novel integration of two process-based models. The first is the Wildfire Human Agency Model (WHAM!), which draws on agent-based approaches to represent anthropogenic fire use and management. The second is JULES-INFERNO, a fire-enabled dynamic global vegetation model, which takes a physically grounded approach to the representation of vegetation-fire dynamics. The combined model enables a coupled socio-ecological simulation of historical burned area. We calibrate the combined model using GFED5 burned area data and perform an independent evaluation using MODIS-based fire radiative power observations. Results suggest that as much as half of all global burned area is generated by managed anthropogenic fires—typically small fires that are lit for, and then spread according to, land user objectives. Furthermore, we demonstrate that including representation of managed anthropogenic fires in a coupled socio-ecological simulation improves understanding of the drivers of unmanaged wildfires. For example, we show how vegetation flammability and landscape fragmentation control inter-annual variability and longer-term change in unmanaged fires. Overall, findings presented here indicate that both socio-economic and climate change will be vital in determining the future trajectory of fire on Earth.
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Journal articleEastwood J, Brown P, Oddy T, et al., 2025,
In flight performance of the MAGIC magnetoresistive magnetometer on the RadCube CubeSat
, Space Science Reviews, Vol: 221, ISSN: 0038-6308In studying space physics, planetary science, and space weather, space-based in situ measurements of the magnetic field are fundamental to understanding underlying physical processes, as well as providing context for other observations. Whilst in many cases instrument design is not severely constrained by the available resource envelope, there are many applications, particularly when using new generations of spacecraft platforms such as CubeSats, that require very low resource sensors. In this context we review the design, development, construction, and flight of the highly miniaturised MAGIC (MAGnetometer from Imperial College) instrument on the RadCube Technology Demonstration CubeSat. MAGIC consists of a boom-mounted (outboard) Anisotropic Magneto-Resistive (AMR) vector sensor connected by harness to a single electronics card inside RadCube. A second inboard AMR vector sensor is mounted on the electronics card. RadCube launched on 17 August 2021 to a sun-synchronous low-Earth polar orbit, with the main mission lasting until April 2022. Routine operations were subsequently extended to the end of 2022, with further special operations in 2023 and 2024 before re-entry on 20 August 2024. Here we review RadCube observations made over more than two years in orbit. Key results from MAGIC on RadCube include meeting ESA space weather magnetic field measurement requirements with both the outboard and inboard sensor, as well as detection of field aligned current signatures at high latitude.
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Journal articleWilson Kemsley S, Nowack P, Ceppi P, 2025,
Climate models underestimate global decreases in high‐cloud amount with warming
, Geophysical Research Letters, Vol: 52, ISSN: 0094-8276Cloud feedback has prevailed as a leading source of uncertainty in climate model projections under increasing atmospheric carbon dioxide. Cloud-controlling factor (CCF) analysis is an approach used to observationally constrain cloud feedback, and subsequently the climate sensitivity. Although high clouds contribute significantly toward uncertainty, they have received comparatively little attention in CCF and other observational analyses. Here we use CCF analysis for the first time to constrain the high-cloud radiative feedback, focusing on the cloud amount component owing to its dominant contribution to uncertainty in high-cloud feedback. Globally, observations indicate larger decreases in high cloudiness than state-of-the-art climate models suggest. In fact, half of the 16 models considered here predict radiative feedbacks inconsistent with observations, likely due to misrepresenting the stability iris mechanism. Despite the suggested strong high-cloud amount decreases with warming, observations point toward a near-neutral net high-cloud amount radiative feedback, owing to almost canceling longwave and shortwave contributions.
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Conference paperBeth A, Galand M, Modolo R, et al., 2025,
Ionospheric environment of Ganymede during the Galileo flybys
, EGU General Assembly, Publisher: EGUThe 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.
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Journal articleKim H, Kang SM, Pendergrass AG, et al., 2025,
Higher precipitation in East Asia and western United States expected with future Southern Ocean warming
, Nature Geoscience, Vol: 18, Pages: 313-321, ISSN: 1752-0894Precipitation over East Asia and the western United States is projected to increase as a result of global warming, although substantial uncertainties persist regarding the magnitude. A key factor driving these uncertainties is the tropical surface warming pattern, yet the mechanisms behind both this warming pattern and the resulting regional precipitation changes remain elusive. Here we use a set of climate model experiments to argue that these changes are partly driven by global teleconnection from the Southern Ocean, which rapidly absorbs anthropogenic heat but releases it with a delay of decades to a century. We show that the delayed Southern Ocean warming contributes to broad tropical ocean warming with an El Niño-like pattern, enhancing precipitation during summer in East Asia and winter in the western United States. The atmospheric teleconnections from the tropical ocean link the Southern Ocean warming to the Northern Hemisphere regional wetting. Southern Hemisphere low clouds are a key regulator of this teleconnection, partly explaining the projected uncertainty of regional precipitation. The documented teleconnection has practical implications: even if climate mitigation reduces carbon dioxide levels, the delayed Southern Ocean warming will sustain a wetter East Asia and western United States for decades to centuries.
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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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