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Journal articleLario D, Hu J, Balmaceda LA, et al., 2026, , Astrophysical Journal, Vol: 998, ISSN: 0004-637X
The fleet of spacecraft distributed across the inner heliosphere during 2024 May–June provided a unique opportunity to analyze, over a broad range of heliolongitudes, the effects produced by the complex sunspot group associated with Active Region 13664. The intense solar activity from 2024 May 8 to 2024 June 21 produced unusually elevated solar energetic particle (SEP) intensities observed at heliocentric distances ≲1 au by Solar Orbiter, Parker Solar Probe, STEREO-A, and near-Earth spacecraft. This activity resulted in a >40 day period of enhanced ≲10 MeV proton intensities spanning at least ∼170° in longitude. Among these events, the 2024 May 20 SEP event was remarkable for its high intensity and wide spatial extent. It was associated with a fast (≳1500 km s<sup>−1</sup>) halo coronal mass ejection (CME) and an X16.5 solar flare located ∼171° in longitude from Earth. Near Earth, the event produced a long-lasting ∼100 MeV proton intensity enhancement with energy spectra flattening between 30 and 80 MeV. It also led to the formation of an energetic particle reservoir that persisted for ∼2 weeks and extended across at least ∼170° in longitude. Several mechanisms contributed to the broad longitudinal spread of SEPs and formation of the energetic particle reservoir, including acceleration at an extended CME-driven shock, particle drifts along the heliospheric current sheet, particle reflection and redistribution caused by the merging of preceding CMEs beyond 1 au, and predominantly cross-field particle transport processes.
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Journal articleMa B, Chen L, Wu D, et al., 2026, , Astrophysical Journal, Vol: 998, ISSN: 0004-637X
The spectral features of 1122 single-band type III-like radio bursts were analyzed statistically using data from the Parker Solar Probe (PSP) during the first nine orbital encounters. After excluding overlapping events, 923 bursts were classified into 706 complete-spectrum (CS) bursts and 217 incomplete-spectrum (IS) bursts depending on radiation completeness. The distribution of start frequency f<inf>st</inf> for IS events (20–54 MHz) was predicted by a lognormal fit. The higher cutoff frequency (f<inf>lo</inf> ∼ 1.2–1.6 MHz) than previous results may be attributed to the limitation of exciting conditions or the radial expansion of guiding magnetic flux tubes. Short durations (1–4 minutes) and low peak fluxes (∼10<sup>3</sup> sfu) indicate that most events are short-time weak bursts. The spectral index of duration versus frequency is near −1, which reflects the influence of velocity dispersion and radio-wave scattering. For the denoised spectra of CS events, the peak frequency of maximal flux (∼4.5 MHz) is obviously higher than those from STEREO (∼1 MHz) and WIND (∼ 2 MHz). This implies that the radiation may be the second or third harmonic wave rather than the fundamental wave. Statistical frequency drift rates follow the classical power-law relation (D<inf>abs</inf> ∝ f<sup>1.84</sup>) and are consistent with simulation results of typical type III radio bursts. CS and IS bursts show similarities in f<inf>lo</inf>, duration, and drift features, but obviously differ in the peak frequency of maximal flux. These results can provide a useful reference for further exploring the emission mechanisms of single-band type III-like radio bursts and the associated energetic electron acceleration processes.
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Journal articleJia H, Quaas J, Kroese W, et al., 2026, , Science Advances, Vol: 12, ISSN: 2375-2548
Aerosol-cloud interactions (ACI) remain the largest uncertainty in anthropogenic climate forcings. Observation-based estimates of instantaneous radiative forcing from ACI (RFaci; the Twomey effect) rely on the choice of aerosol quantities as proxies for cloud condensation nuclei (CCN) concentrations, which differ in their ability to represent cloud-base CCN and data accuracy. Using diverse observations and aerosol-climate models, we evaluate the utility of different proxies with two independent approaches. Both approaches reveal that surface CCN exhibits the smallest bias in predicting RFaci (+5%), followed by aerosol index, surface sulfate and column CCN with similar biases of +25%, while aerosol optical depth and column sulfate show the largest biases (−60% and +92%). Constraining RFaci with the optimal proxy reduces uncertainty from 66 to 43%, yielding a less negative RFaci (−1.0 W m−2) than the unconstrained case (−1.2 W m−2). Our findings highlight the crucial role of proxy constraint in reconciling and improving RFaci estimates.
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Journal articleWilson Kemsley S, Nowack P, Ceppi P, 2026, , Geophysical Research Letters, Vol: 53, ISSN: 0094-8276
Cloud feedback is a dominant source of uncertainty in climate model estimates of equilibrium climate sensitivity (ECS). Cloud controlling factor analysis can observationally constrain cloud feedback. For the first time, we use separate rather than unified frameworks to assess high- and low-cloud feedbacks and constrain the net cloud feedback and subsequently, the ECS. We find a robustly positive cloud feedback (i.e., a negative feedback is <0.5% probable), indicating that clouds amplify global warming. We assess the individual and combined impacts of our cloud feedback constraints on ECS using three approaches. Two indicate an upward ECS shift with reduced uncertainty, preserving ECS–feedback correlations but using cloud feedback as a single line of evidence. The third, a Bayesian framework combining multiple lines of evidence, also suggests a higher ECS but with a smaller increase and broader confidence range.
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Journal articleWivell L, Dougherty MK, Masters A, 2026, , Earth and Space Science, Vol: 13, ISSN: 2333-5084
Saturn's moon Enceladus harbors a global subsurface ocean beneath its icy crust. Understanding the structure and composition of this ocean and ice is critical to assessing its potential habitability. Modern electromagnetic (EM) sounding techniques, which measure a celestial body's induced response to external electromagnetic fields, offer a powerful tool for probing internal structures. These techniques are well-established for Earth and the Moon, modeled for Europa, and here evaluated for Enceladus. By modeling higher frequency range (1 mHz−1 kHz), which sound to shallower depths than lower frequencies, this study shows that induction can provide a constraint on ice composition. The induced response also gives insight into other ice-shell properties, including potential water layers, as well as different stratified ocean conditions. The findings of this study highlight the potential for future missions to use EM sounding to constrain properties of the ice-shell, including composition, as well as identifying potential ocean stratification.
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Journal articleIm U, Samset BH, Nenes A, et al., 2026, , AGU Advances, Vol: 7, ISSN: 2576-604X
Aerosol-cloud interactions (ACI) are a major source of uncertainty in climate science, critically affecting our ability to project near-term climate evolution and assess societal risks. These interactions influence effective radiative forcing, cloud dynamics, and precipitation patterns, yet remain insufficiently constrained due to limitations in observations, modeling, and process understanding. This uncertainty hampers robust policy advice across multiple domains—from estimating remaining carbon budgets and climate sensitivity, to anticipating regional extreme events and evaluating climate interventions such as solar radiation modification. In many cases, the influence of ACI is either underappreciated or excluded from decision-making frameworks due to its complexity and lack of quantification. This perspective outlines a path forward to overcome these barriers by leveraging emerging opportunities in satellite remote sensing, ground-based and airborne observations, high-resolution climate modeling, and machine learning. We identify key areas where rapid progress is feasible, including improved retrievals of cloud microphysical properties, better representation of natural aerosols in a warming world, and enhanced integration of observational and modeling communities. Even as anthropogenic aerosol and its impacts on clouds is reducing owing to emissions controls, addressing ACI uncertainties remains essential for refining climate projections, supporting effective mitigation and adaptation strategies, and delivering actionable science to policymakers in a rapidly changing climate system.
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Journal articleHadid LZ, Chust T, Wahlund JE, et al., 2026, , Journal of Geophysical Research Space Physics, Vol: 131, ISSN: 2169-9380
We report in situ evidence for Enceladus' Alfvén wing system and its coupling with Saturn's ionosphere, based on multi-instrument observations from the Cassini spacecraft. Analysis of 36 events, including 13 from non-flyby paths, confirms the existence of a Main Alfvén Wing (MAW) current system generated at Enceladus, and associated Reflected Alfvén Wings (RAWs) occurring both at Saturn's ionosphere and on the density gradient of Enceladus' plasma torus, extending longitudinally to at least (Formula presented.) ((Formula presented.) 2,000 moon radii) downstream of the moon. Additionally, the observations reveal the systematic existence of a filamentation process of these large-scale Alfvénic perturbations (MAW and RAWs) during their propagation at any distance from their source. These findings demonstrate a more extensive electrodynamic coupling than previously reported for Enceladus and more generally for any moon-magnetosphere interaction. Moreover, the observation of energetic electron depletions and water-group ion signatures at longitudes even further from the moon supports the interpretation of an extended and persistent interaction region. These results highlight Enceladus' role in shaping Saturn's magnetospheric environment and underscore the importance of future missions to exhaustively analyze this type of complex interaction between a moon and a planet.
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Journal articleClear CP, Uylings P, Raassen T, 2026, , Astronomy and Astrophysics (A & A), Vol: 706, ISSN: 0004-6361
Aims. This work reports calculated transition probabilities for spectral lines of singly ionised nickel (Ni II) incorporating newly determined experimental energy levels, addressing critical gaps in atomic data required for astrophysical spectroscopy and plasma diagnostics.Methods. Transition probabilities of Ni II were calculated using the semi-empirical orthogonal operator method for both odd and even energy levels. Calculated eigenvalues were fine-tuned to experimental energy levels, determined using Fourier transform spectroscopy, further increasing the accuracy of these calculated transition probabilities.Results. In total, transition probabilities have been calculated for nearly 118 000 electric dipole transitions between 361 even and 735 odd levels. The resulting transition probabilities show strong agreement with existing experimental and semi-empirical data, while offering improved consistency and coverage across a wide range of line strengths. The calculated transitions span the far-infrared to the vacuum ultraviolet spectral regions, providing extensive coverage for astrophysical applications. This dataset significantly enhances the calculated atomic data available for Ni II and represents a critical contribution to the advancement of our understanding of astrophysical phenomena through improved spectroscopic analysis.
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Conference paperWalach MT, Lam MM, Themens DR, et al., 2026, , Pages: 36-42, ISSN: 1366-8781
Report on the RAS Specialist Discussion Meeting about one of the grand challenges for Earth system scientists.
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Journal articleFargette N, Eastwood JP, Phan TD, et al., 2026, , The Astrophysical Journal, Vol: 997, ISSN: 0004-637X
The heliospheric current sheet (HCS) is an important large-scale structure of the heliosphere, and, for the first time, the Parker Solar Probe (PSP) mission enables us to study its properties statistically, close to the Sun. We visually identify the 39 HCS crossings measured by PSP below 50 R⊙ during encounters 6–21, and investigate the occurrence and properties of magnetic reconnection, the behavior of the spectral properties of the turbulent energy cascade, and the occurrence of kinetic instabilities at the HCS. We find that 82% of the HCS crossings present signatures of reconnection jets, showing that the HCS is continuously reconnecting close to the Sun. The proportion of inward and outward jets depends on heliocentric distance, and the main HCS reconnection X-line has a higher probability of being located close to the Alfvén surface. We also observe a radial asymmetry in jet acceleration, where inward jets do not reach the local Alfvén speed, contrary to outward jets. We find that turbulence levels are enhanced in the ion kinetic range, consistent with the triggering of an inverse cascade by magnetic reconnection. Finally, we highlight the ubiquity of magnetic hole trains in the high-β environment of the HCS, showing that the mirror mode instability plays a key role in regulating the ion temperature anisotropy in HCS reconnection. Our findings shed new light on the properties of magnetic reconnection in the high-β plasma environment of the HCS, its interplay with the turbulent cascade, and the role of the mirror mode instability.
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Journal articleTsilimigkras A, Lazaridis M, Voulgarakis A, et al., 2026, , Theoretical and Applied Climatology, Vol: 157, ISSN: 0177-798X
Most climate change impact studies, regardless of scope, traditionally rely on a predefined set of climate model simulations without thoroughly examining representativeness, model skill, and diversity. This approach risks overlooking regional nuances and limits the utility of projections for tailored adaptation strategies. In the Mediterranean—and particularly Greece, where climate risks are high—addressing these limitations is essential for reliable, actionable projections. The CMIP6 ensemble is extensive, but its size and internal variability pose challenges for regional use, leaving users to navigate an “ensemble of opportunity” with interdependent models and diverse historical and future behaviors. Here we evaluate 35 CMIP6 models over Greece against bias-adjusted GSWP3-W5E5 observations, assessing both annual and seasonal historical performance with multiple diagnostics (correlation, standard deviation, CRMSE, bias, RMSE) and summarizing skill via a composite Historical Performance Score (HPS): the harmonic mean of Taylor Skill Score (pattern fidelity) and a variability-aware bias score that penalizes systematic offsets relative to observed interannual variability. Future responses are analyzed for 2081–2100 (high-emission Shared Socioeconomic Pathway SSP5-8.5) using a quadrant framework based on temperature change (tas) and late-century precipitation (pr); changes in maximum temperature (tasmax) are also incorporated to characterize the amplification of hot conditions. By integrating model performance and ensemble spread, the methodology refines model selection to balance historical credibility with diversity of future outcomes, enabling compact regional sub-ensembles that capture the range from moderate to severe warming and from drier to wetter states. Results show that historical skill does not necessarily translate into capturing future extremes in warming or drying, but a carefully chosen sub-ensemble can maximize the range o
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Journal articleMarrow KE, Strucka J, Merlini S, et al., 2026, , Plasma Physics and Controlled Fusion, Vol: 68, ISSN: 0741-3335
Wepresent results from a new experiment, fielded on the MAGPIE pulsed power generator, producing a rotating, boundary-free plasma with no pre-imposed magnetic field. Angular momentum is introduced to the rotating system by the oblique collision of multiple plasma flows, which aredriven by x-ray ablation of solid targets using the soft x-rays emitted from the implosion of wire array z-pinches. This produces a hydrodynamically stable plasma which undergoes ∼2−3 rotations over the duration of the experiment, significantly more than previous pulsed-power platforms. Estimating the angular frequency from the electron density profile in the inner part of the rotating plasma shows that it has a quasi-Keplerian rotation profile. The system also allows for the addition of a controllable magnetic field. This, combined with the sufficiently large Reynolds (∼105) and magnetic Reynolds (∼10) numbers, will enable investigation of the effect of magnetic field on the structure and stability of the rotating plasma.
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Journal articleMosselmans S, Elizabeth Brindley H, Cox C, et al., 2026, , Atmospheric Science Letters, Vol: 27, ISSN: 1530-261X
The far infrared region plays a critical role in the Earth's greenhouse effect. Measurements across this range are limited and previous studies have found it challenging to achieve radiative closure between different instruments across the mid-far infrared. This study compares high-resolution downwelling spectra measured from the surface in the Arctic to radiative transfer simulations run with atmospheric profiles from a radiosonde, microwave radiometer, and the 5th ECMWF atmospheric reanalysis. The radiosonde-driven simulation generates the closest agreement to the radiance observations. The HATPRO-driven simulation matches within its uncertainty across the entire range. However, it has a larger uncertainty envelope than the other sources. There is a bias in all three simulations associated with underestimated humidity. Our results reiterate the sensitivity of the far infrared to the humidity profile. This suggests that the wider deployment of spectrometers capable of measuring across this region, in parallel with efforts to improve knowledge of far infrared water vapour spectroscopy, could markedly improve our ability to routinely characterise polar environments.
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Journal articleBadman ST, Fargette N, Matteini L, et al., 2026, , Space Science Reviews, Vol: 222, ISSN: 0038-6308
Magnetic switchbacks are fluctuations in the solar wind in which the interplanetary magnetic field sharply deflects away from its background direction so as to create folds in magnetic field lines while remaining of roughly constant magnitude. The magnetic field and velocity fluctuations are extremely well correlated in a way corresponding to Alfvénic fluctuations propagating away from the Sun. For a background field which is nearly radial this causes an outwardly propagating jet to form. Switchbacks and their characteristic velocity jets have recently been observed to be nearly ubiquitous by Parker Solar Probe with in situ measurements in the inner heliosphere within 0.3 AU. Their prevalence, substantial energy content, and potentially fundamental role in the dynamics of the outer corona and solar wind motivate the significant research efforts into their understanding. Here we review the in situ measurements of these structures (primarily by Parker Solar Probe). We discuss how they are identified and measured, and present an overview of the primary observational properties of these structures, both in terms of individual switchbacks and their collective arrangement into “patches”. We identify both properties for which there is a strong consensus and those that have limited or qualified support and require further investigation. We identify and collate several open questions and recommendations for future studies.
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Journal articleDi Natale G, Brindley H, Murray J, et al., 2026, , Atmospheric Chemistry and Physics (ACP), Vol: 26, Pages: 1373-1394, ISSN: 1680-7316
This paper explores whether it is possible to achieve consistency between ground-based infrared radiance measurements made in the presence of cirrus, co-located in-situ aircraft measurements of the cirrus microphysics, and ancillary ground-based remote sensing. Specifically we use spectrally resolved radiances covering the range 400–1500 cm−1, in-situ measurements of cirrus particle sizes and habits, backscatter ceilometer observations of cloud vertical structure and microwave inferred temperature and humidity profiles to investigate whether we can obtain consistency between the derived cloud properties and atmospheric state from these independent sources of data. The primary focus of this study is on the sensitivity of the retrieved cloud particle size to the assumed crystal habit. Excellent consistency between the retrieved cloud parameters is achieved both with the ceilometer derived optical depth and the size distribution measured by the aircraft by assuming the crystal habit to be comprised of bullet rosettes. The averaged values of the effective diameter and optical depth obtained from radiometric measurements are (26.5 ± 1.8) µm and (0.12 ± 0.01) in comparison with the values derived from in-situ and ceilometer measurements equal to (31.5 ± 5.0) µm and (0.13 ± 0.01), respectively. Furthermore, we show that the radiance information contained within the far-infrared (wavenumbers < 650 cm−1) spectrum is critical to achieving this level of agreement with the in-situ aircraft observations. The results emphasize why it is vital to expand the current limited database of measurements encompassing the far-infrared spectrum, particularly in the presence of cirrus, to explore whether this finding holds over a wider range of conditions.
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Journal articleSmith C, Kasoar M, Perkins O, et al., 2026, , PLoS ONE, Vol: 21, ISSN: 1932-6203
Human fire use is a key activity and process in many landscapes and ecosystems around the world, varying spatiotemporally depending on social, economic, and ecological factors. Recently, initiatives have begun to synthesise data on global fire use from across multiple disciplines and disparate sources into coherent databases. Here, we draw on information from one of these databases, the Livelihood Fire Database, which collates data on fire use practices worldwide from case studies in the literature. We examine data from 345 case study locations spanning 69 countries regarding return interval, area burned, and seasonality of anthropogenic fires set to meet small-scale rural livelihood objectives and/or for cultural reasons. We distinguish patterns in the spatiotemporal nature of fires associated with different fire-use purposes, such as clearing vegetation for agriculture, maintaining pasture for livestock, promoting certain plant species for gathering, or driving game when hunting. For many fire uses, especially those related to hunting, gathering, human wellbeing, and social signalling, there are very limited quantitative data available, but it is possible to draw qualitative insights from case studies. Case studies demonstrate that environmental and social conditions drive variation in fire use for the same purpose, reiterating that assumptions of uniform drivers of anthropogenic fire may be misleading. Nonetheless where quantitative data are available, we find some correspondence between the spatiotemporal nature of fires and fire-use purpose, suggesting that distinguishing between different fire-use purposes may be useful to understand and to better model their likely timing, size, and frequency relative to climate and other drivers. We recommend examples where the diagnosis of these broad relationships between fire-use purpose and fire properties could enable improved representation of anthropogenic fire in global land surface models, and aid interpretation of
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Journal articleDai A, Gregory J, Ceppi P, 2026, , Geophysical Research Letters, Vol: 53, ISSN: 0094-8276
The dependence of climate response on the vertical structure of radiative forcing is studied using a set of idealized experiments, with horizontally uniform and vertically confined forcings. We find for a given effective forcing magnitude, higher-altitude forcing causes a smaller global warming, owing to more negative cloud feedback. We present novel evidence relating this altitude dependence to sea-surface temperature patterns and tropospheric static stability. The imposed instantaneous forcings are horizontally uniform, but higher-altitude forcings more effectively suppress convection in the tropical warm pool, producing a more positive effective (adjusted) surface forcing in that region. This gives rise, during the subsequent climate change, to greater warming contrast between the warm pool and rest of the globe, and hence to increase in low cloud amount. Our results show that to achieve accurate climate projections under anthropogenic forcings, it is important to correctly represent the vertical structures of the applied radiative forcing.
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Journal articleEastwood JP, Phan TD, Drake JF, et al., 2026, , The Astrophysical Journal, Vol: 996, ISSN: 0004-637X
The Heliospheric Current Sheet (HCS) is a fundamental feature of the heliosphere, playing a key role organizing the magnetic structure of the solar wind. In contrast to observations previously made through the majority of the heliosphere, Parker Solar Probe has recently revealed that the HCS is typically reconnecting in the inner heliosphere. This provides a new opportunity to study reconnection dynamics in large-scale current sheets and assess how this is different from smaller systems such as Earth’s magnetosphere. We use Parker data to explore HCS reconnection energy partition in two case studies from Encounter 07 and 08. In both cases, we find that in the exhaust, the proton enthalpy flux density is largest, with significant contributions from the proton kinetic energy flux density and electron enthalpy flux density. In contrast, the exhaust Poynting flux density is small in both events. The size and stability of the HCS allows for a control volume analysis to be performed, thus allowing us to estimate changes in energy flux during reconnection. This analysis shows that energy is primarily transferred from the magnetic field to the protons, manifested as the kinetic energy of the exhaust and proton heating. Although the exhaust electron enthalpy flux density is significant, the incoming and outgoing electron enthalpy fluxes are found to be similar, and there is minimal electron heating. The small contribution of the Poynting flux in the outflow may be an important feature of HCS reconnection, with implications for reconnection in large-scale solar and astrophysical current sheets more generally.
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Journal articleGiacalone J, Trotta D, Mitchell DG, et al., 2026, , Astrophysical Journal, Vol: 996, ISSN: 0004-637X
On 2023 March 13, Parker Solar Probe was located about 0.23 au from the Sun when it was crossed by a very fast interplanetary shock. The intensities of ∼0.08–10 MeV energetic protons were markedly enhanced at the shock crossing. At energies from ∼0.1 to 1 MeV, the intensity at the shock was 3–4 orders of magnitude larger than it was ∼4 hr prior. In this study, we investigate the possible source of particles that led to this enhancement. Pre-existing high-energy particles that were present during the few-hour period prior to the shock could possibly serve as a source, assuming they are accelerated to even higher energies by the shock. We apply a “seeds test”—which determines the expected enhancement at the shock—to test this. We find that none of the pre-existing particle populations identified can account for the observed enhancement at the shock. The solar wind itself provides a very abundant source. To test whether shock-heated thermal solar wind could account for the source, we perform a series of self-consistent hybrid plasma simulations of this event and make direct comparisons with the observed particle spectra and magnetic field. We conclude that shock-heated solar wind protons are the source of energetic particles in this event. The direct comparisons of our simulations and observations also suggest that the shock was moving about 1350 km s<sup>−1</sup> and had an Alfvén Mach number of about 4, both of which are considerably lower than previously estimated.
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Journal articleCamacho H, Rotermund KM, Slosar A, et al., 2026, , Open Journal of Astrophysics, Vol: 9
LuSEE-Night is a pathfinder radio telescope on the lunar far side employing four 3-m monopole antennas arranged as two horizontal cross pseudo-dipoles on a rotational stage and sensitive to the radio sky in the 1-50 MHz frequency band. LuSEE-Night measures the corresponding 16 correlation products as a function of frequency. While each antenna combination measures radiation coming from a large area of the sky, their aggregate information as a function of phase in the lunar cycle and rotational stage position can be deconvolved into a low-resolution map of the sky. We study this deconvolution using linear map-making based on the Wiener filter algorithm. We illustrate how systematic effects can be effectively marginalised over as contributions to the noise covariance and demonstrate this technique on beam knowledge uncertainty and gain fluctuations. With reasonable assumptions about instrument performance, we show that LuSEE-Night should be able to map the sub-50 MHz sky at a ∼5-degree resolution.
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Journal articleHartinger MD, Archer MO, Masongsong E, et al., 2026, , Frontiers in Astronomy and Space Sciences, Vol: 13
Ultra Low Frequency (ULF) waves with periods of (Formula presented.) 10–1,000 s can lead to space weather impacts such as induced electrical currents in power grids, thus it is important to understand the factors controlling wave dynamics. This is challenging, however, as waves (1) are affected by multiple factors simultaneously, (2) are non-stationary which in some cases precludes use of identification methods that assume stationarity, (3) can occur in superposition with each other making them difficult to separate and identify. Past studies have addressed these challenges through combined audiovisual analysis tools to identify complex but recurring patterns in ULF wave activity that eluded standard visual inspection and automated detection algorithms, as well as through crowd-sourced wave identification. The “Heliophysics Audified: Resonances in Plasmas” NASA citizen science project follows these studies by deploying a Graphical User Interface (GUI) for crowd-sourced ULF wave identification to a large online audience before and during the Heliophysics Big Year (HBY). In this study, we discuss the initial development, beta testing, and deployment of the GUI in April 2023. We further discuss the key initial scientific findings of the HARP project, in particular the discovery by volunteers of anomalous standing Alfvén wave activity with frequency increasing with distance from the Earth. Finally, we discuss participant impacts and lessons learned, as well broader impacts beyond the scope of the original project such as collaborations with museums and musicians. We place these results in context with previous work and discuss implications for future studies.
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Journal articleBerland GD, Hill ME, Kouloumvakos A, et al., 2026, , ASTROPHYSICAL JOURNAL, Vol: 996, ISSN: 0004-637X
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Conference paperAlterman BL, Livi SA, Lepri ST, et al., 2026, , Pages: 216-223, ISSN: 1743-9213
Charged particle acceleration and heating in the heliosphere requires detailed observa-tions of the velocity distribution functions (VDFs) of these particles across a range of mass and charge states. Such particle energization is often observed concurrent with transient phenom-ena. Proper characterization of such energization processes and their impact on charged particles requires careful consideration of instrument observation timing and the timing at which a tran-sient phenomenon is observed. Solar Orbiter's Heavy Ion Sensor (HIS) observes the composition of the solar wind along with suprathermal and pickup ions. As such, it provides the observations necessary to resolve the mass and charge states appropriate for properly characterizing charged particle energization. In this work, we describe the current status of data aggregation at vari-able time intervals and how that enables proper characterization of charged particle energization concurrent with transient phenomena.
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Journal articleCarter JA, Swamy BN, Lepri ST, et al., 2026, , Ras Techniques and Instruments, Vol: 5
Elfen is a CubeSat mission concept designed to investigate the role of heavy ions in the Earth’s magnetosphere, focusing on both dayside and nightside dynamics. While the significance of heavy and molecular ions is well established in astrophysical contexts, their contribution to solar wind–magnetosphere–ionosphere coupling at Earth remains poorly quantified. On the nightside, the origin and transport mechanisms of ions within the low-latitude plasma sheet are still debated. The mission science questions are based around two overarching questions; What is the heavy ion influence at the dayside magnetosphere? and What is the heavy ion influence on the plasma sheet and on nightside reconnection? Elfen will contribute to this knowledge gap using two primary instruments; a plasma spectrometer for in situ heavy ion composition measurements, and a magnetometer for contextual plasma regime characterization. The payload will be hosted on a cost-effective 16U CubeSat, operating for at least 1 yr. We present the baseline mission architecture developed through a concurrent design facility study and further engineering analysis, designed in conjunction with industrial collaborators and consultants. The proposed orbit, a 12 Earth radii circular trajectory at low inclination with a 59.8-h period, ensures sampling of both upstream and downstream magnetospheric regions, while offering high-science duty cycles and robust ground contact times. Alternative orbital configurations are considered to optimize science return within engineering constraints. Elfen is a timely mission, aligned with growing interest in space weather forecasting and near-Earth space exploration, and it will complement upcoming missions exploring solar-terrestrial interactions.
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Journal articleAndrews MB, Butchart N, Anstey JA, et al., 2026, , EGUsphere, Vol: 2026, Pages: 1-33
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Journal articleShuster JR, Bessho N, Dorelli JC, et al., 2026, , Commun Phys, Vol: 9
The electron diffusion region is central to NASA's Magnetospheric Multiscale (MMS) mission to understand collisionless magnetic reconnection, the plasma physics phenomenon crucial to triggering the explosive energy release of solar flares, powering auroras generated in planetary magnetospheres, and driving sawtooth crashes in laboratory fusion devices. Inside the diffusion region, electron velocity distributions exhibit highly-structured velocity-space signatures critical for elucidating the kinetic mechanisms fueling reconnection. Recent multi-spacecraft analysis techniques enabled observational study of the spatial gradient in the electron velocity distribution, which has been reported in electron-scale current layers to explain the kinetic origins of electron pressure gradients. However, electron gradient distributions have not yet been investigated inside the reconnection diffusion region. In this work, we discover that electron gradient distributions exhibit a smile-shaped velocity-space structure in the electron diffusion region of asymmetric magnetic reconnection at Earth's magnetopause. Characterizing the nature and prevalence of these smile-shaped electron gradient distributions offers a kinetic perspective into how electrons spatially evolve to provide the net electron pressure divergence that self-consistently supports non-ideal electric fields in the electron diffusion region of magnetopause reconnection. These results are relevant to space, astrophysical, and laboratory plasma communities working to understand the long-standing mystery of collisionless magnetic reconnection.
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Journal articleCohen CMS, Alterman BL, Baker DN, et al., 2026, , Space Sci Rev, Vol: 222, ISSN: 0038-6308
The payload of the Interstellar Mapping and Acceleration Probe (IMAP) includes sophisticated in situ instruments to measure solar wind plasma and magnetic fields, suprathermal and energetic particles at 1 au as well as unprecedented remote sensing instruments to observe the energetic neutral atoms (ENAs) in the outer heliosphere and the ultraviolet glow of the interstellar neutral H interacting with the three-dimensional solar wind. This unique combination of sensors on a single platform allows connections to be made between the inner and outer heliosphere to an extent never before possible. This article focuses on the scientific theme of connecting the physics of particle acceleration and transport throughout the heliosphere. Such studies enabled by IMAP are organized into three broad categories: i) fundamental particle acceleration and transport processes, ii) heliospheric variability that affects those processes, and iii) inner heliospheric science.
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Journal articleMartinez Oliveros JC, Krupar V, Ervin T, et al., 2026, , Sol Phys, Vol: 301, ISSN: 0038-0938
Type III solar radio bursts trace electron beams escaping from flares onto interplanetary magnetic fields, yet unambiguous source identification and continuous beam tracking remain challenging. We analyze a Type III event associated with a compact flare in NOAA AR 12887 studied with an unusually complete set of observables: X-ray imaging of the flare site, radio spectro-polarimetry with direction-finding, and multi-point in-situ particle and wave measurements. This synergy delivered two key results. (1) We identify the burst's solar source region by combining the timing consistency between the flare evolution and the radio onset (after accounting for light-travel time) with the sense and degree of circular polarization. The polarization is consistent with emission on topologically open (or quasi-open) field rooted in a compact EUV arcade, as expected for outward-propagating o/x-mode radiation in a diverging flux system. (2) We localize the electron beam and follow its spatio-temporal evolution into the heliosphere by triangulating radio directions and correlating them with time-of-flight signatures in the in-situ electron data. The accompanying Langmuir-wave measurements constrain the characteristic cross-section of the guiding flux tube via the spatial coherence and bandwidth of the wave packets, providing an empirical estimate of the beam's aperture. The magnetic context of AR 12887 shows a complex photospheric field with adjacent open corridors. This configuration could explain the rapid magnetic connectivity between a compact EUV arcade and interplanetary space, and clarifies why strong polarization can arise even when closed loops are present nearby. Together, these observations establish an end-to-end linkage from flare energy release to heliospheric propagation and provide a template for future coordinated studies that require coincident timing, imaging, polarization, radio direction-finding, and in-situ diagnostics to resolve electron escape pathways.
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Journal articleBadman ST, Stevens ML, Bale SD, et al., 2025, , ASTROPHYSICAL JOURNAL LETTERS, Vol: 995, ISSN: 2041-8205
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Journal articleBowen TA, Ervin T, Mallet A, et al., 2025, , Phys Rev Lett, Vol: 135
Collisionless dissipation of turbulence is important for heating plasmas in astrophysical, space physics, and laboratory environments, controlling energy, momentum, and particle transport. We analyze Parker Solar Probe observations to understand the collisionless heating of the sub-Alfvénic solar wind, which is connected to the solar corona. Our results show that linear resonant heating through parallel-propagating cyclotron waves cannot account for turbulent dissipation in the sub-Alfvénic region, which observations suggest may dissipate turbulence at distances further from the Sun. Instead, we find that stochastic heating can account for the observed ion energization; however, because the dominant contributions arise from infrequent, large-amplitude events, turbulent intermittency must be explicitly incorporated. These observations directly connect stochastic heating via breaking of the proton magnetic moment with the intermittent and inhomogeneous heating of turbulence reported in many previous studies. Our identification of stochastic heating as a dynamic mechanism responsible for intermittent heating of the solar wind has significant implications for turbulent dissipation in the lower corona, other astrophysical environments, and laboratory plasmas.
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