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Journal articleKrämer E, Koller F, Suni J, et al., 2025,
Jets Downstream of Collisionless Shocks: Recent Discoveries and Challenges
, Space Science Reviews, Vol: 221, ISSN: 0038-6308Plasma flows with enhanced dynamic pressure, known as magnetosheath jets, are often found downstream of collisionless shocks. As they propagate through the magnetosheath, they interact with the surrounding plasma, shaping its properties, and potentially becoming geoeffective upon reaching the magnetopause. In recent years (since 2016), new research has produced vital results that have significantly enhanced our understanding on many aspects of jets. In this review, we summarise and discuss these findings. Spacecraft and ground-based observations, as well as global and local simulations, have contributed greatly to our understanding of the causes and effects of magnetosheath jets. First, we discuss recent findings on jet occurrence and formation, including in other planetary environments. New insights into jet properties and evolution are then examined using observations and simulations. Finally, we review the impact of jets upon interaction with the magnetopause and subsequent consequences for the magnetosphere-ionosphere system. We conclude with an outlook and assessment on future challenges. This includes an overview on future space missions that may prove crucial in tackling the outstanding open questions on jets in the terrestrial magnetosheath as well as other planetary and shock environments.
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Journal articleWahlund J-E, Bergman JES, Ahlen L, et al., 2025,
The Radio & Plasma Wave Investigation (RPWI) for the JUpiter ICy moons Explorer (JUICE)
, Space Science Reviews, Vol: 221, ISSN: 0038-6308The Radio & Plasma Wave Investigation (RPWI) onboard the ESA JUpiter ICy moons Explorer (JUICE) is described in detail. The RPWI provides an elaborate set of state-of-the-art electromagnetic fields and cold plasma instrumentation, including active sounding with the mutual impedance and Langmuir probe sweep techniques, where several different types of sensors will sample the thermal plasma properties, including electron and ion densities, electron temperature, plasma drift speed, the near DC electric fields, and electric and magnetic signals from various types of phenomena, e.g., radio and plasma waves, electrostatic acceleration structures, induction fields etc. A full wave vector, waveform, polarization, and Poynting flux determination will be achieved. RPWI will enable characterization of the Jovian radio emissions (including goniopolarimetry) up to 45 MHz, has the capability to carry out passive radio sounding of the ionospheric densities of icy moons and employ passive sub-surface radar measurements of the icy crust of these moons. RPWI can also detect micrometeorite impacts, estimate dust charging, monitor the spacecraft potential as well as the integrated EUV flux. The sensors consist of four 10 cm diameter Langmuir probes each mounted on the tip of 3 m long booms, a triaxial search coil magnetometer and a triaxial radio antenna system both mounted on the 10.6 m long MAG boom, each with radiation resistant pre-amplifiers near the sensors. There are three receiver boards, two Digital Processing Units (DPU) and two Low Voltage Power Supply (LVPS) boards in a box within a radiation vault at the centre of the JUICE spacecraft. Together, the integrated RPWI system can carry out an ambitious planetary science investigation in and around the Galilean icy moons and the Jovian space environment. Some of the most important science objectives and instrument capabilities are described here. RPWI focuses, apart from cold plasma studies, on the understanding of how, thr
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Journal articleLiu Y-H, Hesse M, Genestreti K, et al.,
Ohm's Law, the Reconnection Rate, and Energy Conversion in Collisionless Magnetic Reconnection
, Space Science Reviews -
Journal articleFlegrová M, Brindley H, 2025,
Two Decades of Fire-Induced Albedo Change and Associated Short-Wave Radiative Effect Over Sub-Saharan Africa
, Journal of Geophysical Research: Atmospheres, Vol: 130, ISSN: 2169-897XWe present an analysis of 20 years of fire and albedo data in Africa. We show that, in the mean, the sub-Saharan Africa post-fire surface albedo anomaly can be parameterized using an exponential recovery function, recovering from a decrease of (Formula presented.) immediately after a fire with a time constant of (Formula presented.) days. Although the magnitude of albedo changes shows large spatial and temporal variations and a strong land cover type (LCT) dependency, exponential recovery is observed in the majority of LCTs. We show that fires cause long-term surface brightening, with an Africa-wide albedo increase of (Formula presented.) 10 months after a fire, but we find this is driven almost exclusively by slow vegetation recovery in the Kalahari region, confirming previous findings. Using downward surface shortwave flux (DSSF) estimates, we calculate the fire-induced surface radiative forcing (RF), peaking at (Formula presented.) Wm−2 in the burn areas, albeit with a significantly smaller effect when averaged temporally and spatially. We find that the long-term RF in months 5–10 after a burn averaged over the continent is negative because of the brightening observed. Despite a well-documented reduction in burning in Africa in the recent decades, our temporal analysis does not indicate a decrease in the overall fire-induced RF likely due to large interannual variability in albedo anomaly and DSSF data. However, we observe a decline in the short-term RF in southern hemisphere Africa, driven by both a reduction in fires and changes in LCT distributions.
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Journal articlePayne DS, Swisdak M, Eastwood JP, et al., 2025,
In-situ observations of the magnetothermodynamic evolution of electron-only reconnection
, Communications Physics, Vol: 8 -
Conference paperMurray-Watson R, Gryspeerdt E, 2025,
Air mass history linked to the development of Arctic mixed-phase clouds
<jats:p>The development of clouds during marine cold-air outbreaks (MCAOs) represent a complex phenomenon, transitioning from stratocumulus decks near ice edges to cumuliform fields downwind. This change cloud morphology changes the radiative properties of the cloud, and therefore is of importance to the surface energy budget. Therefore, it is crucial to understand the factors which may drive transition to a broken cloud field. Previous in situ and modelling studies suggest the formation of ice may enhance precipitation and therefore accelerate break-up. However, little is known about the development of mixed-phase clouds in MCAOs.&#160;This study uses pseudo-Lagrangian trajectories and satellite data to analyze this mixed-phase cloud development. We observe a rapid transition from liquid to ice phases in MCAO clouds, contrasting with similar cloud formations outside MCAO conditions. These mixed-phase clouds initially form at temperatures below -20&#176;C near ice edges but can dominate even at -13&#176;C further into outbreaks. This temperature shift suggests a significant role for biological ice nucleating particles (INPs), which increase in prevalence as air masses age over marine environments. The study also notes the influence of the air mass's history over snow- and ice-covered surfaces, which may be low in INPs, on cloud evolution. This link helps explain seasonal variations in Arctic cloud development, both during and outside of MCAOs. Our findings emphasize the importance of understanding local marine aerosol sources and the broader INP distribution in the Arctic for accurate cloud phase modeling in the region.&#160;</jats:p>
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Conference paperBeth A, Galand M, Modolo R, et al., 2025,
Ionospheric environment of Ganymede during the Galileo flybys
<jats:p>The Galileo spacecraft flew by Ganymede, down to 0.1 RG from the surface for the closest, six times giving us insight into its plasma environment. Its ionosphere, made of ions born from the ionisation of neutrals present in Ganymede&#8217;s exosphere, represents the bulk of the plasma near the moon around closest approach. As it has been revealed by Galileo and Juno, near closest approach the ion population is dominated by low-energy ions from the water ion group (O+, HO+, H2O+) and O2+. However, little is known about their density, spatial distribution, and effect on the surface weathering of the moon itself. Galileo G2 flyby has been extensively studied. Based on a comparison between observations and 3D test-particle simulations, Carnielli et al. (2020a and 2020b) confirmed the ion composition (debated at the time), highlighted the inconsistency between the assumed exospheric densities and the observed ionospheric densities, and derived the contribution of ionospheric ions as an exospheric source. However, other flybys of Ganymede are also available (e.g. G1, G7, G8, G28, and G29) providing in-situ measurements at different phases of Ganymede around Jupiter or jovian magnetospheric conditions at the moon. We extend the original study by Carnielli et al. to other flybys, and compare our modelled ion moments (ion number density, velocity, and energy distribution) with Galileo in-situ data. We discuss our results and contrast them with those obtained for the G2 flyby.&#160;&#160;</jats:p>
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Conference paperLewis Z, Beth A, Galand M, et al., 2025,
Constraining ion transport in the diamagnetic cavity of comet 67P
<jats:p>Comets are small icy bodies originating from the outer solar system that produce an increasingly dense gas coma through sublimation as they approach perihelion. Photoionisation of this gas results in a cometary ionosphere, which interacts with the impinging solar wind, leading to large scale plasma structures. One such structure is the diamagnetic cavity: the magnetic field-free inner region that the solar wind cannot penetrate. This region was encountered many times by the ESA Rosetta mission, which escorted comet 67P/Churyumov-Gerasimenko for a two-year section of its orbit.Within the diamagnetic cavity, high ion bulk velocities have been observed by the Rosetta Plasma Consortium (RPC) instruments. The fast ions are thought to have been accelerated by an ambipolar electric field, but the nature and strength of this field are difficult to determine analytically. Our study therefore aims to model the impact of various electric field profiles on the ionospheric density profile and ion composition. The 1D numerical model we have developed includes three key ion species (H2O+, H3O+, and NH4+) in order to assess the sensitivity of each to the timescale of plasma loss through transport. NH4+ is of particular interest, as it has been previously shown to be the dominant ion species at low cometocentric distances near perihelion. It is only produced through the protonation of NH3, a minor component of the neutral gas, and we show that this makes it particularly sensitive to the electric field.We also compare the simulated electron density to RPC datasets, to find the electric field strength and profile which best recreate the plasma densities measured inside the diamagnetic cavity near perihelion. From this, we also constrain the radial bulk ion speed that is required to explain the observations with the model.</jats:p>
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Journal articleAmes F, Ferreira D, Czaja A, et al.,
Ocean stratification impedes particulate transport to the plumes of Enceladus
, Nature Communications, ISSN: 2041-1723 -
Journal articleKaweeyanun N, Masters A, 2025,
Three-dimensional modelling of Ganymede’s Chapman–Ferraro magnetic field and its role in subsurface ocean induction
, Icarus, Vol: 426, ISSN: 0019-1035In April 2023, the Jupiter Icy Moons Explorer (Juice) began its journey to orbit Jupiter’s largest and only magnetic moon, Ganymede. Part of the mission’s objectives aim to verify existence of the moon’s subsurface ocean and determine its structure through its induced response to external excitation by periodically varying magnetic field. Known contributions to the excitation are those from Jupiter’s dipole (at synodic period) and quadrupole (at half-synodic period) variations, and Ganymede’s inclined eccentric orbit around Jupiter (at orbital period). We propose that Ganymede’s magnetopause, where the Chapman–Ferraro (C–F) magnetic field arises from local currents, also contributes to subsurface ocean induction. This article introduces the first three-dimensional model of the C–F field and its outputs at Ganymede’s subsurface ocean and larger magnetosphere. The field is shown to be non-uniform — strongest near upstream Ganymede’s subflow region and gradually weakening away from it. Magnetopause asymmetry due to the Jovian guide field results in largely synodic variation of the C–F field, with exceptions near Ganymede’s equator and subflow meridian where asymmetry effects are minimal and the variations are half-synodic. The C–F field amplitude is of general order ∼50 nT, which is significant relative to excitation from the Jovian field. Comparisons to Galileo data and magnetohydrodynamic simulation results suggest the model is useful, therefore the magnetopause effects must be considered in future induction modeling of Ganymede’s subsurface ocean ahead of the Juice mission.
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Journal articleSharan S, Dougherty M, Masters A, et al.,
Viability of the early JUICE flyby trajectories to confirm ocean existence at Ganymede
, The Planetary Science Journal, ISSN: 2632-3338 -
Journal articleZhang J, Chen Y-S, Gryspeerdt E, et al., 2025,
Radiative forcing from the 2020 shipping fuel regulation is large but hard to detect
, Communications Earth & Environment, Vol: 6<jats:title>Abstract</jats:title> <jats:p>Reduction in aerosol cooling unmasks greenhouse gas warming, exacerbating the rate of future warming. The strict sulfur regulation on shipping fuel implemented in 2020 (IMO2020) presents an opportunity to assess the potential impacts of such emission regulations and the detectability of deliberate aerosol perturbations for climate intervention. Here we employ machine learning to capture cloud natural variability and estimate a radiative forcing of +0.074 ±0.005 W m<jats:sup>−2</jats:sup> related to IMO2020 associated with changes in shortwave cloud radiative effect over three low-cloud regions where shipping routes prevail. We find low detectability of the cloud radiative effect of this event, attributed to strong natural variability in cloud albedo and cloud cover. Regionally, detectability is higher for the southeastern Atlantic stratocumulus deck. These results raise concerns that future reductions in aerosol emissions will accelerate warming and that proposed deliberate aerosol perturbations such as marine cloud brightening will need to be substantial in order to overcome the low detectability.</jats:p>
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Journal articleWang JH, Horbury TS, Matteini L, et al., 2025,
Alpha–proton relative drift: implications for the origins and dynamics of the solar wind
, Letters of the Astrophysical Journal, Vol: 978, ISSN: 2041-8205Helium nuclei (alpha particles) strongly influence the momentum and energy balance in the solar wind, comprising up to 20% of the solar wind mass density. In fast Alfvénic wind at heliocentric distances greater than 0.3 au, the alpha particles' bulk flow speed is systematically different to that of the protons. This relative drift speed is of unknown origin and is often close to the local Alfvén wave speed. Novel Parker Solar Probe measurements of the solar wind below 0.3 au show that, closer to the Sun, the alpha–proton drift speed remains on the order of 100–200 km s−1, even where the Alfvén speed is greater than 600 km s−1. This relative speed is quantitatively similar to oxygen–hydrogen drift speeds observed in the transition region by remote sensing, suggesting similar selective acceleration processes in the corona. Due to the relative speed of the Alfvén wave to each particle population close to the Sun, the alphas fluctuate with velocity amplitudes comparable to those of the protons, altering the energy balance of the wave. As a result, alpha particles carry a significant fraction of the total kinetic energy in Alfvénic fluctuations in the near-Sun solar wind. The alpha–proton drift speed is comparable to the proton speed in the near-Sun wind, making the bulk flow of the alpha particles a significant contribution to the kinetic energy flux. These heavy-ion dynamics provide new observational constraints on quantifying the energy budget of the solar wind and the magnetic field evolution through the heliosphere.
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Journal articleMaunder M, Foullon C, Forsyth R, et al., 2025,
Longitudinally Spaced Observations of a Magnetic Cloud-Like Structure Embedded in a Co-rotating Interaction Region
, Annales Geophysicae: atmospheres, hydrospheres and space sciences, ISSN: 0992-7689 -
Journal articleLow J, Teoh R, Ponsonby J, et al., 2025,
Ground-based contrail observations: Comparisons with reanalysis weather data and contrail model simulations
, Atmospheric Measurement Techniques, Vol: 18, Pages: 37-56, ISSN: 1867-1381Observations of contrails are vital for improving our understanding of the contrail formation and life cycle, informing models, and assessing mitigation strategies. Here, we developed a methodology that utilises ground-based cameras for tracking and analysing young contrails (< 35 min) formed under clear-sky conditions, comparing these observations against reanalysis meteorology and simulations from the contrail cirrus prediction model (CoCiP) with actual flight trajectories. Our observations consist of 14 h of video footage recorded over 5 different days in Central London, capturing 1582 flight waypoints from 281 flights. The simulation correctly predicted contrail formation and absence for around 75 % of these waypoints, with incorrect contrail predictions occurring at warmer temperatures than those with true-positive predictions (7.8 K vs. 12.8 K below the Schmidt-Appleman criterion threshold temperature). When evaluating contrails with observed lifetimes of at least 2 min, the simulation's correct prediction rate for contrail formation increases to over 85 %. Among all waypoints with contrail observations, 78 % of short-lived contrails (observed lifetimes < 2 min) formed under ice-subsaturated conditions, whereas 75 % of persistent contrails (observed lifetimes > 10 min) formed under ice-supersaturated conditions. On average, the simulated contrail geometric width was around 100 m smaller than the observed (visible) width over its observed lifetime, with the mean underestimation reaching up to 280 m within the first 5 min. Discrepancies between the observed and simulated contrail formation, lifetime, and width can be associated with uncertainties in reanalysis meteorology due to known model limitations and sub-grid-scale variabilities, contrail model simplifications, uncertainties in aircraft performance estimates, and observational challenges, among other possible factors. Overall, this study demonstrates the potential of ground-based cameras to create
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Journal articleHall RJ, Czaja A, Danabasoglu G, et al., 2025,
A new robust frontal disturbance index of the Oyashio Extension sea surface temperature front
, Journal of Climate, Vol: 38, Pages: 293-307, ISSN: 0894-8755The Oyashio Extension (OE) frontal zone in the northwest Pacific Ocean is associated with strong gradients of sea surface temperature (SST) and salinity. The OE front enhances baroclinicity and anchors the storm tracks; changes in its position and strength may impact atmospheric variability. North–south shifts in the OE front are often defined using the leading principal component for the latitude of the absolute maximum SST gradient in the northwest Pacific (145°–170°E), the so-called Oyashio Extension index (OEI). We show that the OEI is sensitive to the choice of SST dataset used in its construction, and that the significance of regressions of atmospheric fields onto the OEI also depends on the choice of SST datasets, leading to nonrobust results. This sensitivity primarily stems from the longitudinal domain used to define the OEI including a region with parallel or indistinct frontal zones in its central section (155°–164°E), leading to divergent results across datasets. We introduce a new index that considers the extent to which the SST front across this central section departs from climatology, the frontal disturbance index (FDI). For the months considered and over short time lags, the FDI produces more consistent results on air–sea interactions and associated high-frequency storm-track metrics than the conventional OEI, with a southward shift of the storm track for a more positive FDI. The FDI appears to be related to oceanic mesoscale eddy activity in the central OE region. There are significant asymmetric associations between the FDI and storm-track metrics dependent on the sign of the FDI.
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Journal articleAcevski M, Masters A, 2024,
Enhanced precipitation of energetic protons due to Uranus' asymmetric magnetic field
, Geophysical Research Letters, Vol: 51, ISSN: 0094-8276Uranus remains one of the most unexplored planets in our solar system, featuring a distinctive magnetic field structure first observed by NASA's Voyager 2 mission almost 40 years ago. Uranus is particularly notable for its pronounced magnetic field asymmetry, a characteristic unique to the icy giants. Here we show that, in the region where Voyager 2 did not pass (< 4 Ru), the asymmetric magnetic field can distort the trajectories of high energy protons within Uranus' radiation belts such that the particles hit the planet when they otherwise would not have (in a traditional dipole field). This implies that radiation belt protons which start with pitch angles well outside their respective loss cones can drift into a region where the loss cone is much bigger and then precipitate. This occurs preferentially in the magnetic north pole due to its significantly weaker surface field strength.
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Journal articleLewis HC, Stawarz JE, Matteini L, et al., 2024,
Turbulent Energy Conversion Associated With Kinetic Microinstabilities in Earth's Magnetosheath
, GEOPHYSICAL RESEARCH LETTERS, Vol: 51, ISSN: 0094-8276 -
Journal articleHarrison JA, Pearce PM, Yang F, et al., 2024,
Evaluating potential power output of terrestrial thermoradiative diodes with atmospheric modelling
, iScience, Vol: 27, ISSN: 2589-0042A thermoradiative diode is a device that can generate power through thermal emission from the warm Earth to the cold night sky. Accurate assessment of the potential power output requires knowledge of the downwelling radiation from the atmosphere. Here, accurate modelling of this radiation is used alongside a detailed balance model of a diode at the Earth’s surface temperature to evaluate its performance under nine different atmospheric conditions. In the radiative limit, these conditions yield power densities between 0.34 and 6.5 W.m-2, with optimal bandgaps near 0.094 eV. Restricting the angles of emission and absorption to less than a full hemisphere can marginally increase the power output. Accounting for non-radiative processes, we suggest that if a 0.094 eV device would have radiative efficiencies more than two orders of magnitude lower than a diode with a bandgap near 0.25 eV, the higher bandgap material is preferred.
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Journal articleHuang Z, Velli M, Shi C, et al., 2024,
Dominance of 2 Minute Oscillations near the Alfven Surface
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 977, ISSN: 2041-8205 -
Journal articleDing M, Kozuki H, Concepcion F, et al., 2024,
Laboratory confirmation and improved accuracy of 4f and 5d energy levels of Fe ii previously identified from stellar spectra
, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 536, Pages: 274-279, ISSN: 0035-8711 -
Journal articleTippett A, Gryspeerdt E, Manshausen P, et al., 2024,
Weak liquid water path response in ship tracks
, Atmospheric Chemistry and Physics, Vol: 24, Pages: 13269-13283, ISSN: 1680-7316The assessment of aerosol–cloud interactions remains a major source of uncertainty in understanding climate change, partly due to the difficulty in making accurate observations of aerosol impacts on clouds. Ships can release large numbers of aerosols that serve as cloud condensation nuclei, which can create artificially brightened clouds known as ship tracks. These aerosol emissions offer a “natural”, or “opportunistic”, experiment to explore aerosol effects on clouds, while also disentangling meteorological influences. Utilizing ship positions and reanalysis wind fields, we predict ship track locations, colocating them with satellite data to depict the temporal evolution of cloud properties after an aerosol perturbation. Repeating our analysis for a null experiment does not necessarily recover zero signal as expected; instead, it reveals subtleties between different null-experiment methodologies. This study uncovers a systematic bias in prior ship track research, due to the assumption that background gradients will, on average, be linear. We correct for this bias, which is linked to the correlation between wind fields and cloud properties, to reveal the true ship track response.We find that, once this bias is corrected for, the liquid water path (LWP) response after an aerosol perturbation is weak on average. This has important implications for estimates of radiative forcings due to LWP adjustments, as previous responses in unstable cases were overestimated. A noticeable LWP response is only recovered in specific cases, such as marine stratocumulus clouds, where a positive LWP response is found in precipitating or clean clouds. This work highlights subtleties in the analysis of isolated opportunistic experiments, reconciling differences in the LWP response to aerosols reported in previous studies.
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Journal articleHanna E, Francis J, Wang M, et al., 2024,
Influence of high-latitude blocking and the northern stratospheric polar vortex on cold-air outbreaks under Arctic amplification of global warming
, ENVIRONMENTAL RESEARCH-CLIMATE, Vol: 3 -
Book chapterBeth A, Galand M, Simon Wedlund C, et al., 2022,
Cometary Ionospheres: An Updated Tutorial
, Comets III, Editors: Meech, Combi, Bockelée-Morvan, Raymond, Zolensky, Publisher: University of Arizona Press, ISBN: 9780816553648This chapter aims at providing the tools and knowledge to understand and model the plasma environment surrounding comets in the innermost part near the nucleus. In particular, our goal is to give an updated post-Rosetta view of this ionised environment: what we knew, what we confirmed, what we overturned, and what we still do not understand.
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Journal articleRovithakis A, Voulgarakis A, 2024,
Wildfire aerosols and their impact on weather: a case study of the August 2021 fires in Greece using the WRF‐Chem model
, Atmospheric Science Letters, Vol: 25, ISSN: 1530-261XWildfires are significant contributors to atmospheric gases and aerosols, impacting air quality and composition. This pollution from fires also affects radiative forcing, influencing short-term weather patterns and climate dynamics. Our research employs the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) to investigate the repercussions of wildfires on aerosol abundances and associated immediate weather responses. We examine the summer season of 2021, a period marked by severe wildfire events in the country during a heatwave period. We conducted sensitivity experiments including and excluding wildfire emissions to measure their effects on aerosol optical depth (AOD), radiative forcing, and weather features such as temperature, humidity, clouds, and atmospheric circulation. Our findings demonstrate that the radiative impacts of wildfires negatively influence the local temperature over the fire smoke plume-affected areas. Conversely, neighbouring areas of continental Greece experience increases in temperature due to remote effects of wildfire emissions, caused by meteorological feedbacks that reduce atmospheric humidity. Crucially, including fire emissions significantly improves the simulated surface temperatures predicted by the model over the Greek domain. Our work demonstrates that wildfire-generated aerosols can significantly impact weather conditions and highlights the importance of including both local radiative effects and remote feedback for achieving more accurate weather prediction.
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Journal articleDing M, Ryabtsev AN, Kononov EY, et al., 2024,
Spectrum and energy levels of the high-lying singly excited configurations of Nd III: New Nd III experimental energy levels and wavelengths, with transition probability and ionisation energy calculations
, ASTRONOMY & ASTROPHYSICS, Vol: 692, ISSN: 0004-6361 -
Journal articleNykyri K, Di Matteo S, Archer MO, et al., 2024,
Could a low‐frequency perturbation in the Earth's magnetotail be generated by the lunar wake?
, Geophysical Research Letters, Vol: 51, ISSN: 0094-8276Both ground based magnetometers and ionospheric radars at Earth have frequently detected Ultra Low Frequency (ULF) fluctuations at discrete frequencies extending below one mHz-range. Many dayside solar wind drivers have been convincingly demonstrated as driver mechanisms. In this paper we investigate and propose an additional, nightside generation mechanism of a low frequency magnetic field fluctuation. We propose that the Moon may excite a magnetic field perturbation of the order of 1 nT at discrete frequencies when it travels through the Earth's magnetotail 4–5 days every month. Our theoretical prediction is supported by a case study of ARTEMIS magnetic field measurements at the lunar orbit in the Earth's magnetotail. ARTEMIS detects statistically significant peaks in magnetic field fluctuation power at frequencies of 0.37–0.47 mHz that are not present in the solar wind.
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Journal articleZeng Z, Yao Z, Liu J, et al., 2024,
Ultralow-frequency waves in Jupiter’s magnetopause boundary layer
, The Astrophysical Journal: an international review of astronomy and astronomical physics, Vol: 976, ISSN: 0004-637XUltralow-frequency (ULF) waves (∼tens of minutes period) are widely identified in the Jovian system and are believed to be associated with energy dissipation in the magnetosphere and ionosphere. Due to the magnetodisk oscillation related to planetary rotation, it is challenging to identify the periodicities inside the magnetosphere, although remote sensing observations of the polar emissions provide clear evidence of the tens of minutes pulsations. In this study, we take advantage of Juno's in situ measurements in the magnetopause boundary layer for a long duration, i.e., >4 hr, to directly assess the tens of minutes periodicities of the boundary dynamics caused by the interactions between the internal plasma and external solar wind. Through periodogram analysis on the magnetic field and particle data, we find ULF waves with periodicities of ∼18 minutes, ∼40 minutes, and ∼70–80 minutes, which is generally consistent with pulsations in multiple remote sensing observations. A multiple-harmonic ULF phenomenon was also identified in the observations. The periodicities from in situ measurements provide crucial clues in understanding the origin of pulsating wave/auroral emissions in the Jovian system. The results could also further our understanding of energy transfer and release between the internal plasma of Jupiter and external solar wind.
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Journal articleLai T, Toumi R, 2024,
Sensitivity of the energy conversion efficiency of tropical cyclones during intensification to sea surface temperature and static stability
, Quarterly Journal of the Royal Meteorological Society, ISSN: 0035-9009It is projected that the sea surface temperature (SST) increases under climate change and enhances tropical cyclone (TC) intensification directly. An opposing expected feature of climate change is the strengthening atmospheric static stability, which may suppress intensification. The intensity and diabatic heating are closely related through the secondary circulation, but it has been unclear whether both will change at the same rate. Here we show that they respond differently to stability changes. The efficiency of converting diabatic heating to kinetic energy (KE) of TCs to SST and static stability during the intensification stage is examined. In a set of idealised simulations, the efficiency does not have a significant relation with the SST. However the efficiency is found to decrease with increasing static stability at a rate of about K. It is shown that the KE increment declines, while the diabatic heating in the eyewall remains unchanged with larger static stability. The decrease in KE gain at the eyewall is associated with an enhanced outward advection of absolute angular momentum. The combined effect of enhanced water‐vapour supply and the slightly reduced updraft at the eyewall keeps the diabatic heating steady with varying static stability. This study demonstrates the complex effects of enhanced static stability, which is expected to accompany surface warming, on tropical cyclones.
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Journal articleOpie S, Verscharen D, Chen CHK, et al., 2024,
Temperature anisotropy instabilities driven by intermittent velocity shears in the solar wind
, JOURNAL OF PLASMA PHYSICS, Vol: 90, ISSN: 0022-3778
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