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Journal articleErgun RE, Qi Y, Vo T, et al., 2025, , ASTROPHYSICAL JOURNAL, Vol: 993, ISSN: 0004-637X
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Journal articleCuesta ME, Fraschetti F, Livadiotis G, et al., 2025, , ASTROPHYSICAL JOURNAL LETTERS, Vol: 993, ISSN: 2041-8205
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Journal articleMcComas DJ, Christian ER, Schwadron NA, et al., 2025, , SPACE SCIENCE REVIEWS, Vol: 221, ISSN: 0038-6308
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- Citations: 3
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Journal articleKim H, Nakamura R, Grimmich N, et al., 2025, , Geophysical Research Letters, Vol: 52, ISSN: 0094-8276
This study presents comprehensive observations of intense high-speed jets (HSJs) and their global impacts on the inner magnetosphere and ionosphere, using multi-satellite and ground-based observations. Cluster-4, located near the bow shock, observed signatures associated with foreshock transients generated by a solar wind directional discontinuity. Downstream of the bow shock, THEMIS-A, positioned post-noon (∼12.8 MLT) in the magnetosheath, detected a sunward plasma flow prior to crossing into the magnetosphere. Nearly simultaneously, THEMIS-E, inside the magnetosphere at ∼13.4 MLT, suddenly crossed into the magnetosheath and observed intense earthward HSJs. The strong compression of the magnetopause current sheet forced GOES-13 to temporarily enter the magnetosheath, while SuperDARN radars registered enhanced poleward ionospheric convection and magnetometers detected signatures of westward currents. These sequential observations provide a rare, integrated demonstration of how an upstream foreshock disturbance transfers energy and momentum throughout the coupled magnetosphere-ionosphere system.
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Journal articleGuillaume-Castel R, Ceppi P, Dorrington J, et al., 2025, , Geophysical Research Letters, Vol: 52, ISSN: 0094-8276
The spatial pattern of sea surface temperature (SST) affects the global radiative budget through the “pattern effect.” While previous studies highlighted the role of El Niño–Southern Oscillation (ENSO) in unforced pattern effect, a systematic assessment of the dominant modes of SST variability for the top of atmosphere energy budget has been lacking. Using Partial Least Squares Regression, we identify Eastern Pacific and Modoki ENSO as the two leading modes most relevant to the pattern effect at interannual timescales. These ENSO variants exhibit distinct radiative signatures due to subtle shifts in the location of SST anomalies relative to the climatological warm pool. Furthermore, analysis of individual ENSO events indicates that each event has a unique radiative signature depending on its evolving spatial structure. These findings highlight the importance of accounting for ENSO diversity to accurately understand how modes of SST variability influence the global energy budget.
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Journal articleErvin T, Mallet A, Eriksson S, et al., 2025, , ASTROPHYSICAL JOURNAL LETTERS, Vol: 992, ISSN: 2041-8205
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Journal articleBreul P, Ceppi P, Nowack P, 2025, , Atmospheric Chemistry and Physics (ACP), Vol: 25, Pages: 11991-12005, ISSN: 1680-7316
Stratocumulus clouds are thought to exert a strong positive radiative feedback on climate change, but recent analyses suggest that this feedback is widely under-represented in global climate models. To assess the broader implications of this model error for the simulated climate change responses, we investigate the impact of Pacific stratocumulus cloud feedback on projected warming patterns, equilibrium climate sensitivity and tropical atmospheric circulation under increased CO2 concentrations. Using the Community Earth System Model, with modifications to enhance low-cloud-cover sensitivity to sea surface temperature (SST) anomalies in Pacific stratocumulus regions, we find increased tropical SST variability and persistence, a higher equilibrium climate sensitivity, an enhanced east–west warming contrast across the tropical Pacific, and a stronger slowdown of the Walker circulation under 4×CO2 conditions. Our findings are supported by inter-model relationships across CMIP6 4×CO2 simulations. These results underscore the importance of accurately representing cloud feedback in climate models to predict future climate change impacts not only globally but also on a regional scale, such as warming patterns or circulation change.
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Journal articleTsui EYL, Toumi R, 2025, , Atmospheric Science Letters, Vol: 26, ISSN: 1530-261X
The study of tropical cyclones re-entering the ocean or making ‘seafall’ has been limited. Here, idealised simulations are used to study the re-intensification of seafalling tropical cyclones. They follow a two-stage fast-slow process driven predominately by a change in surface friction initially and then by heating. The previous land decay causes seafalling tropical cyclones to be larger and intensify more slowly with milder inner-core contraction than in ocean-only cases. Nonetheless, they reach the same intensity but with almost twice the integrated kinetic energy, so that the second landfall made by seafalling tropical cyclones can cause more damage due to their larger footprint of destructive wind.
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Journal articleWaters CL, Eastwood JP, Fargette N, et al., 2025, , Journal of Geophysical Research: Space Physics, Vol: 130, ISSN: 2169-9380
Magnetic reconnection is inherently structured, with distinct spatial regions such as inflows, outflows, and separatrices playing key roles in energy conversion and particle transport. While in situ spacecraft measurements provide detailed local information, determining where a spacecraft lies within the global reconnection geometry remains a major challenge. Proxy-based methods are often ambiguous, while full reconstructions require strong assumptions and are difficult to apply systematically across events. Here, we present a method that bridges these approaches by using machine learning to infer global structural context from local measurements. We first apply k-means clustering to a 2.5-D particle-in-cell simulation to identify six characteristic symmetric reconnection regions. A recurrent neural network (RNN) is then trained on spacecraft-like trajectories through the simulation to classify time series data into these regions. When applied to Magnetospheric Multiscale (MMS) observations of magnetotail reconnection, this method successfully identifies regional transitions, including inflow, outflow, and separatrix crossings, in agreement with previous reconstructions where available. The approach provides a practical, scalable, and automated framework for determining spatial context in reconnection events without requiring full geometric reconstruction, enabling large-scale and efficient statistical studies of reconnection dynamics across multiple events.
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Journal articleArcher M, Evans V, Eastwood J, et al., 2025, , Space Weather, Vol: 23, ISSN: 1539-4956
Field-aligned currents (FACs) are the main physical mechanism behind magnetosphere–ionosphere coupling, with these currents communicating environmental changes between the two regions of geospace. Field-aligned currents are thus a key factor in monitoring space weather, both from an operational and scientific perspective. While the AMPERE project has demonstrated that engineering fluxgate magnetometers on commercial satellite constellations can be assimilated to estimate the FACs across the entire polar cap, a limiting factor in the spatio-temporal resolution of this assimilation is the coverage of measurement points. However, in recent years much larger satellite mega-constellations have been launched into low Earth orbit (LEO) which might offer unprecedented opportunities. Here we leverage engineering anisotropic magnetoresistive magnetometer data from the OneWeb constellation for the first time. A case study during the 12 May 2021 geomagnetic storm is presented. We show conclusive evidence that OneWeb engineering magnetometers were able to detect FAC signatures present during this event by validating against AMPERE magnetic field and current maps from the same time. However, this result was despite significant challenges due to the OneWeb spacecraft instrumentation, data availability, and magnetic cleanliness, which we discuss in detail. Finally, we provide an outlook on the next steps required for OneWeb magnetic field data to provide valuable contributions to space weather science and operations.
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Journal articleCargill PJ, Hood AW, Johnson D, 2025, , Monthly Notices of the Royal Astronomical Society, Vol: 542, Pages: 3385-3394, ISSN: 0035-8711
Conductive cooling of the solar corona at a magnetic null is examined. An initial equilibrium is set up, balancing thermal conduction and a constant spatially uniform coronal heating. The heating is then turned off and the subsequent conductive cooling calculated. An equation for the cooling is obtained using the method of separation of variables and it is shown that the equations for the equilibrium between conduction and heating, and the time-dependent cooling are mathematically identical with a simple change of variables. Thus, the properties of the cooling phase are automatically determined by the equilibrium state. For a two-dimensional null, the characteristic cooling time-scale increases over that in a straight field by a factor of between 2 and 5, with a scaling determined by the ratio of the average and base areas of a flux element. There is no explicit dependence on the very large areas that can arise near the null.
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Journal articleDesai RT, Perrin J, Meredith NP, et al., 2025, , SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS, Vol: 23
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Journal articleDing M, Lim SZJ, Yu X, et al., 2025, , MACHINE LEARNING-SCIENCE AND TECHNOLOGY, Vol: 6
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Journal articleTrotta D, Horbury TS, Giacalone J, 2025, , ASTRONOMY & ASTROPHYSICS, Vol: 702, ISSN: 0004-6361
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Journal articleAuestad H, Shibu A, Ceppi P, et al., 2025, , Geophysical Research Letters, Vol: 52, ISSN: 0094-8276
Midlatitude storms transport warm and moist air poleward and upward, releasing latent heat. Latent heating is thus organized by the circulation but then modifies temperature gradients and winds, constituting a nonlinear feedback. We define the latent heating feedback as the effects that arise from latent heating being coupled with the circulation. Because of its nonlinearity, the climatic effects of this feedback are difficult to isolate and remain poorly understood. By decoupling latent heating from the circulation in an atmospheric general circulation model, we show that the latent heating feedback enhances storm track eddy diffusivity, modifying eddy heat fluxes beyond changes in mean baroclinicity. Simultaneously, tracked storms occur at lower latitudes, intensify more, and propagate further poleward, while the subtropical jet strengthens as coupled latent heating preserves lower latitude baroclinicity. The feedback response supports the idea that diabatic effects cause the “too zonal, too equatorward” storm track biases in climate models.
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Conference paperLin J, Gryspeerdt E, Clark R, 2025, , 9th Conference on Neural Information Processing Systems (NeurIPS 2025)
There has been great progress in improving numerical weather prediction and climate models using machine learning. However, most global models act at akilometer-scale, making it challenging to model individual clouds and factors such as extreme precipitation, wind gusts, turbulence, and surface irradiance. Therefore, there is a need to move towards higher-resolution models, which in turn require high-resolution real-world observations that current instruments struggle to obtain. We present Cloud4D, the first learning-based framework that reconstructs a physically consistent, four–dimensional cloud state using only synchronized ground-based cameras. Leveraging a homography-guided 2D-to-3D transformer, Cloud4D infers the full 3D distribution of liquid water content at 25 m spatial and 5 s temporal resolution. By tracking the 3D liquid water content retrievals over time, Cloud4D additionally estimates horizontal wind vectors. Across a two-month deployment comprising six skyward cameras, our system delivers an order-of-magnitude improvement in space-time resolution relative to state-of-the-art satellite measurements, while retaining single-digit relative error (< 10%) against collocated radar measurements. Code and data are available on our projectpage https://cloud4d.jacob-lin.com/.
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Journal articleKawaguchi K, Ceppi P, 2025, , Geophysical Research Letters, Vol: 52, ISSN: 0094-8276
The sea surface temperature (SST) pattern modulates the Earth's radiative feedbacks at decadal timescales. However, decadal feedback variations over the historical period depend on the choice of climate model, even when forced with the same SST data set. We investigate these differences through analyzing amip-piForcing output, focusing on low cloud feedback. Time-variation in low cloud feedback results primarily from the SST pattern, mediated by changes in near-global lower tropospheric stability (LTS). We investigate the meteorological factors contributing to low cloud feedback variation through the cloud controlling factor analysis method, diagnosing cloud radiative sensitivities from 16 CMIP5 and CMIP6 models, and an observational constraint from MODIS. We find the radiative sensitivity of models to LTS in the stratocumulus regions dominates the magnitude of cloud feedback time variation due to the pattern effect. Additionally, models underestimate low cloud radiative sensitivity to changes in LTS and SST and thus the time-variation in feedback.
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Journal articleHuang Z, Velli M, Chandran BDG, et al., 2025, , Astrophysical Journal Letters, Vol: 990, ISSN: 2041-8205
The 1/f noise is a ubiquitous phenomenon in natural systems. Since the advent of space exploration, the 1/f range has been consistently observed in in situ solar wind measurements throughout the heliosphere, sparking decades of debate regarding its origin. Recent Parker Solar Probe observations near the Alfvén surface have revealed a systematic absence of the 1/f range above 10¯鈦碒z in pristine solar wind, providing a unique opportunity to investigate its origin in solar wind turbulence. Despite numerous observations of the 1/f range at varying frequencies, no study has systematically examined its properties across different solar wind conditions. Here, we identify two distinct types of 1/f ranges in solar wind turbulence: the fast/Alfvénic wind type and the slow/mixed wind type. The fast/Alfvénic type appears to be an intrinsic feature of Alfvénic turbulence, while the slow/mixed type resembles classical flicker noise. For the fast/Alfvénic type, we find a near-perfect WKB evolution of the frequency-averaged fluctuation amplitude and an intriguing migration pattern in frequency space. For the slow/mixed type, we examine the solar cycle dependence of the 1/f noise using the OMNI (LRO) data set spanning solar cycles 22–25. We also analyze the autocorrelation function of the magnetic field vectors and identify a clear relationship between the 1/f range and the decline in correlation, as well as unexpected resonance peaks in the autocorrelation function.
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Journal articleRivera YJ, Klein KG, Wang JH, et al., 2025, , Astrophysical Journal Letters, Vol: 990, ISSN: 2041-8205
Over decades of solar wind observations, heavy ions have been observed to have a higher temperature and flow faster than protons in the solar corona and heliosphere. Remote observations have largely been limited to the low corona (<4 R鈯), while in situ observations for heavy ions (Z > 2) have only been sampled at 1 au and beyond. As a result, theories that address heavy ion heating and acceleration remain largely unconstrained. With the launch of Solar Orbiter, heavy ion kinetics can be probed closer to the Sun, as close as the orbit of Mercury (65 R鈯), to examine their radial behavior. Through a statistical analysis of O6+, this work provides a comprehensive analysis of the velocity and temperature of O6+ from 0.3 to 1 au. The study finds that the O6+ relative drift, normalized to the local Alfvén speed, and its temperature compared to protons both decrease with distance from the Sun and show some speed dependence. The O6+ temperature is well fit by a single temperature adiabatic profile across all wind speeds, suggesting that there is no significant heating at these heliocentric distances, which is in contrast to what is observed for protons and He2+. Alfvénic fluctuations, some with full 180鈭 field rotation, create momentary negative differential streaming where the speed of O6+ trails the protons. The amount of negative differential streaming gradually increases at larger distances. These results provide critical constraints on the proposed mechanisms seeking to describe ion heating and acceleration in the solar wind.
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Journal articleKrasnoselskikh V, Jebaraj IC, Cooper TRF, et al., 2025, , ASTROPHYSICAL JOURNAL, Vol: 990, ISSN: 0004-637X
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Journal articleRovithakis A, Burke E, Burton C, et al., 2025, , Natural Hazards and Earth System Sciences, Vol: 25, Pages: 3185-3200, ISSN: 1561-8633
Our previous studies have shown that fire weather conditions in the Mediterranean and specifically over Greece are expected to become more severe with climate change, impling potential increases in burnt area. Here, we employ the Joint UK Land Environment Simulator (JULES) coupled with the INFERNO fire model driven by future climate projections from the UKESM1 model to investigate the repercussions of climate change and future vegetation changes on burnt area over Greece. We validate modelled burnt area against the satellite-derived GFED5 dataset, and find the model's performance to be good, especially for the more fire-prone parts of the country in the south Greece. For future simulations, we use future climate data following three Shared Socioeconomic Pathways (SSPs), consisting of an optimistic climate change scenario where fossil fuel emissions peak and decline beyond 2020 (SSP126), a middle-of-the-road scenario (SSP370), and a pessimistic scenario where emissions continue to rise throughout the century (SSP8.5). Our results show increased burnt area in the future compared to the present-day period in response to overall hotter and drier climatological conditions. We use an additional JULES-INFERNO simulation in which dynamic vegetation was activated, and find that it features smaller future burned area increases compared to our simulation with static present-day vegetation. For this dynamically changing vegetation simulation the greatest burnt area increases are found for southern Greece, due to higher future availability of flammable and heat-resistant needleleaf trees and the smallest decreases in agricultural areas of northern Greece due to a reduction in the aforementioned tree category.
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Journal articleSakellaris IA, Bartzis JG, Grillakis E, et al., 2025, , FIRE TECHNOLOGY, ISSN: 0015-2684
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Journal articleElsden T, Southwood DJ, Allanson O, et al., 2025, , Journal of Geophysical Research: Space Physics, Vol: 130, ISSN: 2169-9380
The plasmapause in Earth's magnetosphere represents the boundary between the plasma which co-rotates with the Earth (plasmasphere), and the more tenuous plasmatrough outside. The density change across the plasmapause can be large, changing by approximately 1–2 orders of magnitude depending on the prevailing conditions. This would suggest it to be a location where magnetohydrodynamic (MHD) surface waves can form, and indeed, this has been proposed in previous works to explain ultra-low frequency (ULF) wave observations around the plasmapause location. The main question is how such a large scale surface wave on the plasmapause would be excited. In this paper, we propose a model whereby surface waves at the plasmapause are driven by energy input from the magnetopause through solar wind driving. We derive an analytical form for the amplitude of these surface waves with this new driven boundary condition at the magnetopause. The excitation of these waves is then tested in several MHD simulations, where the model geometry, wavenumbers and temporal dependence of the magnetopause driver are varied. We establish that surface waves on the plasmapause can be excited by driving from the magnetopause, and that this still occurs with impulsive and continuous broadband driving. The azimuthal scale of the wave is a critical factor for this excitation, with longer azimuthal scales more favorable for driving larger amplitude surface waves. This mechanism provides new insight for how large scale and large amplitude ULF waves can access the inner magnetosphere, with potential implications for their interaction with radiation belt particles.
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Journal articlePanditharatne S, Cox C, Song R, et al., 2025, , Atmospheric Chemistry and Physics, Vol: 25, Pages: 9981-9998, ISSN: 1680-7316
Studies have indicated that far-infrared radiances hold significant information about the microphysics of ice clouds, particularly the ice crystal habit. In support of the European Space Agency's Far-Infrared Outgoing Radiation Understanding and Monitoring mission, we perform the first retrieval on an observation of coincident upwelling far- and mid-infrared radiances taken from an aircraft above a cirrus cloud layer. Four retrievals are performed: including and neglecting the far-infrared portion of the spectrum and assuming two different habit mixes. Results are compared to in situ measurements of the cloud optical thickness, cloud top height, cloud effective radius, and habit distributions. We find that despite the known limitations of ice cloud optical property models, all the retrievals show agreement within the in situ measurements of the cloud optical thickness, cloud top height, and cloud effective radius. However, the inclusion of the far-infrared enables a distinction between two different habits that is not possible using only mid-infrared channels. Furthermore, in this case study, the uncertainty in the retrieval of cloud top height and cloud optical thickness halves with the inclusion of the far-infrared. As with other studies, we also see an additional degree of freedom for the temperature and water vapour retrievals. Our study highlights the need for the improvement of current ice cloud optical models, with the radiance residuals from the converged retrievals still exceeding the instrument uncertainty within the far-infrared. However, it provides observational support for the theoretical improvement that far-infrared observations could bring to retrievals of ice cloud properties.
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Journal articleFrankignoul C, Hall R, Kwon Y-O, et al., 2025, , JOURNAL OF CLIMATE, Vol: 38, Pages: 5055-5066, ISSN: 0894-8755
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Journal articleKoike M, Takigawa M, Morimoto S, et al., 2025, , POLAR SCIENCE, Vol: 45, ISSN: 1873-9652
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- Citations: 2
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Journal articlePathak N, Ergun RE, Vo T, et al., 2025, , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 130, ISSN: 2169-9380
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Journal articleToumi R, Sparks N, 2025, , Journal of Catastrophe Risk and Resilience, Vol: 03, ISSN: 3049-7604
Statistical hurricane risk assessments make long-term multi-decadal stationary climate assumptions, but there is large hurricane variability in the risk. It would be useful to also better estimate the “current” risk. The hurricane damage index (HurDI), is proposed as a measure of the underlying non-stationary risk. The HurDI is defined as the normalised annual average damage calculated with a stochastic wind only model, a single damage function, and uniform exposure across the continental U.S. The stochastic model is climate conditioned by weighting the historical basin hurricane counts, potential intensity, and tracks. The weights are chosen to give the best persistence forecast for each parameter for the next five years. There has been a substantial increase of the hurricane risk as measured by the HurDI. In 2024, the index was at a record high of 188, with a reference value of 100 in 1989. The HurDI is a dynamic view of risk based on the hurricane variability only and can be compared to U.S. property catastrophe reinsurance rates. There are periods of varying difference between the rates and the HurDI reflecting the volatile market cycles.
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Journal articleBowen TA, Mallet A, Dunn CI, et al., 2025, , ASTRONOMY & ASTROPHYSICS, Vol: 700, ISSN: 0004-6361
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Journal articleNorgren C, Chen L-J, Graham DB, et al., 2025, , Space Science Reviews, Vol: 221, ISSN: 0038-6308
Magnetic reconnection is a fundamental plasma process responsible for the sometimes explosive release of magnetic energy in space and laboratory plasmas. Inside the diffusion regions of magnetic reconnection, the plasma becomes demagnetized and decouples from the magnetic field, enabling the change in magnetic topology necessary to power the energy release over larger scales. Since it was launched in 2015, the Magnetospheric MultiScale (MMS) mission has significantly advanced the understanding of the particle dynamics key to magnetic reconnection by providing high-resolution, in-situ measurements able to resolve ion and electron kinetic scales, i.e. a fraction of a gyroradius, that have confirmed theoretical predictions, revealed new phenomena, and refined existing models. These breakthroughs are critical for understanding not only space plasmas but also laboratory and astrophysical plasmas where magnetic reconnection occurs. In this work, we review the ion and electron dynamics occurring within the diffusion regions, in the inflow, along the separatrices, and downstream of the diffusion regions, in different reconnection configurations: symmetric, asymmetric, antiparallel, and guide field reconnection.
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