Publications

Journal article

Owens MJ, Lockwood M, Barnard LA, Yardley SL, Hietala H, LaMoury AT, Vuorinen Let al., 2023,

Annual Variations in the Near-Earth Solar Wind

, SOLAR PHYSICS, Vol: 298, ISSN: 0038-0938

Cite

Journal article

Archer M, Southwood D, Hartinger M, Rastatter L, Nykyri Ket al., 2023,

Magnetosonic ULF waves with anomalous plasma - magnetic field correlations: standing waves and inhomogeneous plasmas

, Geophysical Research Letters, Vol: 50, Pages: 1-13, ISSN: 0094-8276

Ultra-low frequency (ULF) wave observations across the heliosphere often rely on the sign of correlations between plasma (density/pressure) and magnetic field perturbations to distinguish between fast and slow magnetosonic modes. However, the assumptions behind this magnetohydrodynamic result are not always valid, particularly within the magnetosphere which is inhomogeneous and supports standing waves along the geomagnetic field. Through theory and a global simulation, we find both effects can result in anomalous plasma–magnetic field correlations. The interference pattern in standing waves can lead both body and surface magnetosonic waves to have different cross-phases than their constituent propagating waves. Furthermore, if the scale of gradients in the background are shorter than the wavelength or the waves are near-incompressible, then advection by the wave of inhomogeneities can overcome the wave's inherent sense of compression. These effects need to be allowed for and taken into account when applying the typical diagnostic to observations.

Journal article

Li Y, Tang Y, Wang S, Toumi R, Song X, Wang Qet al., 2023,

Recent increases in tropical cyclone rapid intensification events in global offshore regions

, Nature Communications, Vol: 14, ISSN: 2041-1723

Rapid intensification (RI) is an essential process in the development of strong tropical cyclones and a major challenge in prediction. RI in offshore regions is more threatening to coastal populations and economies. Although much effort has been devoted to studying basin-wide temporal-spatial fluctuations, variations of global RI events in offshore regions remain uncertain. Here, we show that compared with open oceans, where the annual RI counts do not show significant changes, offshore areas within 400 km of the coastline have experienced a significant increase in RI events, with the count tripling from 1980 to 2020. Furthermore, thermodynamic environments present more favorable conditions for this trend, and climate models show that global ocean warming has enhanced such changes. This work yields an important finding that an increasing threat of RI in coastal regions has occurred in the preceding decades, which may continue under a future warming climate.

Journal article

Murray-Watson R, Gryspeerdt E, Goren T, 2023,

Investigating the development of clouds within marine cold air outbreaks

, Atmospheric Chemistry and Physics, Vol: 23, Pages: 9365-9383, ISSN: 1680-7316

Marine cold air outbreaks are important parts of the high-latitude climate system, and are characterised by strong surface fluxes generated by the air-sea temperature gradient. These fluxes promote cloud formation, which can be identified in satellite imagery by the distinct transformation of stratiform cloud ‘streets’ into a broken field of cumuliform clouds downwind of the outbreak. This evolution in cloud morphology changes the radiative properties of the cloud, and therefore is of importanceto the surface energy budget. While the drivers of stratocumulus-to-cumulus transitions, such as aerosols or the sea surface temperature gradient, have been extensively studied for subtropical clouds, the factors influencing transitions at higher latitudes are relatively poorly understood. This work uses reanalysis data to create a set of composite trajectories of cold air outbreaks moving off the Arctic ice edge and co-locates these trajectories with satellite data to generate a unique view of liquid-dominated cloud development within cold air outbreaks.The results of this analysis show that clouds embedded in cold-air outbreaks have distinctive properties relative to clouds following other trajectories in the region. The initial strength of the outbreak shows a lasting effect on cloud properties, with differences between clouds in strong and weak events visible over 30 hours after the air has left the ice edge. However, while the strength (measured by the magnitude of the marine cold-air outbreak index) of the outbreak affects the magnitude of cloud properties, it does not affect the timing of the transition to cumuliform clouds nor the top-of-atmosphere albedo. In contrast, the initial aerosol conditions do not strongly affect the magnitude of the cloud properties, but are correlated to cloud break-up,leading to an enhanced cooling effect in clouds moving through high aerosol conditions due to delayed break-up. Both the aerosol environment and the strength and

Journal article

Trotta D, Pezzi, Burgess D, Preisser L, Blanco-Cano X, Kajdic P, Hietala H, Horbury TS, Vainio R, Dresing N, Retino A, Marcucci MF, Sorriso-Valvo L, Servidio S, Valentini Fet al., 2023,

Three-dimensional modelling of the shock-turbulence interaction

, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 525, Pages: 1856-1866, ISSN: 0035-8711

Cite

Journal article

Horbury T, Bale S, mcmanus M, Larson D, Kasper J, Laker R, Matteini L, Raouafi N, Velli M, Woodham L, Woolley T, Fedorov A, Louarn P, Kieokaew R, Durovcova T, Chandran B, Owen Cet al., 2023,

Switchbacks, microstreams and broadband turbulence in the solar wind

, Physics of Plasmas, Vol: 30, ISSN: 1070-664X

Switchbacks are a striking phenomenon in near-Sun coronal hole flows, but their origins, evolution, and relation to the broadband fluctuations seen farther from the Sun are unclear. We use the near-radial lineup of Solar Orbiter and Parker Solar Probe during September 2020 when both spacecraft were in wind from the Sun's Southern polar coronal hole to investigate if switchback variability is related to large scale properties near 1 au⁠. Using the measured solar wind speed, we map measurements from both spacecraft to the source surface and consider variations with source Carrington longitude. The patch modulation of switchback amplitudes at Parker at 20 solar radii was associated with speed variations similar to microstreams and corresponds to solar longitudinal scales of around 5°–10°. Near 1 au⁠, this speed variation was absent, probably due to interactions between plasma at different speeds during their propagation. The alpha particle fraction, which has recently been shown to have spatial variability correlated with patches at 20 solar radii, varied on a similar scale at 1 au⁠. The switchback modulation scale of 5°–10°, corresponding to a temporal scale of several hours at Orbiter, was present as a variation in the average deflection of the field from the Parker spiral. While limited to only one stream, these results suggest that in coronal hole flows, switchback patches are related to microstreams, perhaps associated with supergranular boundaries or plumes. Patches of switchbacks appear to evolve into large scale fluctuations, which might be one driver of the ubiquitous turbulent fluctuations in the solar wind.

Abstract
Cite

Journal article

Zazzeri G, Graven H, Xu X, Saboya E, Blyth L, Manning AJ, Chawner H, Wu D, Hammer Set al., 2023,

Radiocarbon measurements reveal underestimated fossil CH₄ and CO₂ emissions in London

, Geophysical Research Letters, Vol: 50, ISSN: 0094-8276

Radiocarbon (14C) is a powerful tracer of fossil emissions because fossil fuels are entirely depleted in 14C, but observations of 14CO2 and especially 14CH4 in urban regions are sparse. We present the first observations of 14C in both methane (CH4) and carbon dioxide (CO2) in an urban area (London) using a recently developed sampling system. We find that the fossil fraction of CH4 and the atmospheric concentration of fossil CO2 are consistently higher than simulated values using the atmospheric dispersion model NAME coupled with emission inventories. Observed net biospheric uptake in June–July is not well correlated with simulations using the SMURF model with NAME. The results show the partitioning of fossil and biospheric CO2 and CH4 in cities can be evaluated and improved with 14C observations when the nuclear power plants influence is negligible.

Journal article

Livi S, Lepri ST, Raines JM, Dewey RM, Galvin AB, Louarn P, Collier MR, Allegrini F, Alterman BL, Bert CM, Bruno R, Chornay DJ, D'Amicis R, Eddy TJ, Ellis L, Fauchon-Jones E, Fedorov A, Gershkovich I, Holmes J, Horbury TS, Kistler LM, Kucharek H, Lugaz N, Nieves-Chinchilla T, O'Brien H, Ogasawara K, Owen CJ, Phillips M, Ploof K, Rivera YJ, Spitzer SA, Stubbs TJ, Wurz Pet al., 2023,

First results from the Solar Orbiter Heavy Ion Sensor

, ASTRONOMY & ASTROPHYSICS, Vol: 676, ISSN: 0004-6361

Cite
Citations: 20

Journal article

Lewis HC, Stawarz JE, Franci L, Matteini L, Klein K, Salem CS, Burch JL, Ergun RE, Giles BL, Russell CT, Lindqvist P-Aet al., 2023,

Magnetospheric Multiscale measurements of turbulent electric fields in earth's magnetosheath: how do plasma conditions influence the balance of terms in generalized Ohm's law?

, Physics of Plasmas, Vol: 30, ISSN: 1070-664X

Turbulence is ubiquitous within space plasmas, where it is associated with numerous nonlinear interactions. Magnetospheric Multiscale (MMS) provides the unique opportunity to decompose the electric field (E) dynamics into contributions from different linear and nonlinearprocesses via direct measurements of the terms in generalized Ohm’s law. Using high-resolution multipoint measurements, we compute the magnetohydrodynamic (EMHD), Hall (EHall), electron pressure (EPe ), and electron inertia (Einertia) terms for 60 turbulent magnetosheath intervals, to uncover the varying contributions to the dynamics as a function of scale for different plasma conditions. We identify key spectral characteristics of the Ohm’s law terms: the Hall scale, kHall, where EHall becomes dominant over EMHD; the relative amplitude of EPe to EHall, which is constant in the sub-ion range; and the relative scaling of the nonlinear and linear components of EMHD and of EHall, which are independent of scale. We find expressions for the characteristics as a function of plasma conditions. The underlying relationship between turbulent fluctuation amplitudes and ambient plasma conditions is discussed. Depending on the interval, we observe that EMHD and EHall can be dominated by either nonlinear or linear dynamics. We find that EPe is dominated by its linear contributions, with a tendency for electron temperature fluctuations to dominate at small scales. The findings are not consistent with existing linear kinetic Alfven wave theory for isothermal fluctuations. Our work shows how contributions to turbulent dynamics change in different plasma conditions, which may provide insight into other turbulent plasma environments.

Journal article

Zhu X, He J, Duan D, Verscharen D, Owen CJ, Fedorov A, Louarn P, Horbury TSet al., 2023,

Non-field-aligned Proton Beams and Their Roles in the Growth of Fast Magnetosonic/Whistler Waves: Solar Orbiter Observations

, ASTROPHYSICAL JOURNAL, Vol: 953, ISSN: 0004-637X

Cite
Citations: 5

Journal article

Heyns MJ, Lotz SI, Cilliers PJ, Gaunt CTet al., 2023,

Adaptations to a geomagnetic field interpolation method in Southern Africa

, ADVANCES IN SPACE RESEARCH, Vol: 72, Pages: 854-865, ISSN: 0273-1177

Journal article

Misal H, Varela E, Voulgarakis A, Rovithakis A, Grillakis M, Kountouris Yet al., 2023,

Assessing public preferences for a wildfire mitigation policy in Crete, Greece

, Forest Policy and Economics, Vol: 153, Pages: 1-16, ISSN: 1389-9341

The increased frequency and severity of wildfires in the Mediterranean region generates significant damages in ecosystems and landscapes while harming human populations. Institutional complexities, along with socioeconomic and demographic changes encouraging development into the wildland-urban interface, rural abandonment, and focus on fire suppression, are increasing the vulnerability and flammability of Mediterranean ecosystems. Developing effective strategies for managing wildfire incidence and its aftermath requires understanding of the public preferences for wildfire policy characteristics. Here we elicit public preferences for wildfire mitigation policies employing a stated choice experiment applied in Crete, Greece. A region with typical Mediterranean landscape experiencing significant development and rural-to-urban migration that disrupts existing fire regimes. We estimate conditional logit, mixed logit and latent class models to study the general public's preferences and willingness to pay for limiting wildfire frequency and agricultural land burnt, maintaining landscape features, and managing post-wildfire recovery. Results of our study show that measures to manage post-wildfire damage are consistently valued as the most positive amongst the sampled respondents, achieving values that range between €25.92 in conditional logit model to €46 in one of the latent classes identified. Improving the landscape quality follows in importance, although it shows more heterogeneity in the responses. The latent class approach allowed to identify that those associated with either the agricultural or the tourism sector of the sampled individuals, displayed significantly different preferences for the proposed attributes. Overall, our findings indicate that there is a strong preference amongst the general public to shift current policies based on suppression towards more integrated approaches dealing both with prevention and post-fire management. The outcomes of th

Journal article

Vuorinen L, LaMoury AT, Hietala H, Koller Fet al., 2023,

Magnetosheath Jets Over Solar Cycle 24: An Empirical Model

, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 128, ISSN: 2169-9380

Cite
Citations: 8

Journal article

Kilpua E, Vainio R, Cohen C, Dresing N, Good S, Ruohotie J, Trotta D, Bale SD, Christian E, Hill M, McComas DJ, McNutt R, Schwadron Net al., 2023,

Energetic ion enhancements in sheaths driven by interplanetary coronal mass ejections

, ASTROPHYSICS AND SPACE SCIENCE, Vol: 368, ISSN: 0004-640X

Cite
Citations: 7

Journal article

Adhikari S, Shay M, Parashar T, Matthaeus W, Pyakurel P, Stawarz J, Eastwood Jet al., 2023,

Effect of a guide field on the turbulence like properties of magnetic reconnection

, Physics of Plasmas, Vol: 30, Pages: 1-14, ISSN: 1070-664X

The effect of an external guide field on the turbulence-like properties of magneticreconnection is studied using five different 2.5D kinetic particle-in-cell (PIC) simulations. The magnetic energy spectrum is found to exhibit a slope of approximately−5/3 in the inertial range, independent of the guide field. On the contrary, theelectric field spectrum, in the inertial range steepens more with the guide field andapproaches a slope of −5/3. In addition, spectral analysis of the different terms ofthe generalized Ohm’s law is performed and found to be consistent with PIC simulations of turbulence and MMS observations. Finally, the guide field effect on theenergy transfer behavior is examined using von-K´arm´an Howarth (vKH) equationbased on incompressible Hall-MHD. The general characteristics of the vKH equationwith constant rate of energy transfer in the inertial range, is consistent in all the simulations. This suggests that the qualitative behavior of energy spectrum, and energytransfer in reconnection is similar to that of turbulence, indicating that reconnectionfundamentally involves an energy cascade.

Journal article

Lewis ZM, Beth A, Altwegg K, Galand M, Goetz C, Heritier K, ORourke L, Rubin M, Stephenson Pet al., 2023,

Origin and trends in NH4+ observed in the coma of 67P

, Monthly Notices of the Royal Astronomical Society, Vol: 523, Pages: 6208-6219, ISSN: 0035-8711

The European Space Agency/Rosetta mission escorted comet 67P/Churyumov–Gerasimenko and witnessed the evolution of its coma from low activity (∼2.5–3.8 au) to rich ion-neutral chemistry (∼1.2–2.0 au). We present an analysis of the ion composition in the coma, focusing on the presence of protonated high proton affinity (HPA) species, in particular NH4+⁠. This ion is produced through the protonation of NH3 and is an indicator of the level of ion-neutral chemistry in the coma. We aim to assess the importance of this process compared with other NH4+ sources, such as the dissociation of ammonium salts embedded in dust grains. The analysis of NH4+ has been possible thanks to the high mass resolution of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis/Double Focusing Mass Spectrometer (ROSINA/DFMS). In this work, we examine the NH4+ data set alongside data from the Rosetta Plasma Consortium instruments, and against outputs from our in-house ionospheric model. We show that increased comet outgassing around perihelion yields more detections of NH4+ and other protonated HPA species, which results from more complex ion-neutral chemistry occurring in the coma. We also reveal a link between the low magnetic field strength associated with the diamagnetic cavity and higher NH4+ counts. This suggests that transport inside and outside the diamagnetic cavity is very different, which is consistent with 3D hybrid simulations of the coma: non-radial plasma dynamics outside the diamagnetic cavity is an important factor affecting the ion composition.

Journal article

Kang H, Choi Y-S, 2023,

Radiative effects of observationally constrained tropical upper-level clouds in a radiative-convective equilibrium model

, Climate Dynamics, Vol: 61, Pages: 1903-1912, ISSN: 0930-7575

<jats:title>Abstract</jats:title><jats:p>Tropical upper-level clouds (TUCs) control the radiation budget in a climate system and strongly influence surface temperatures. This study examines global mean surface temperature changes due to the percent change in TUC cover, which is referred to as the tropical upper-level cloud radiative effect (TUCRE, in units of Kelvin per %). We use a radiative-convective equilibrium model that can control both upper- and lower-level cloud layers separately in three idealized regions (extratropics, tropical moist, and tropical dry regions) and two sub-regions (clear-moist and cloudy-moist regions) within the tropical moist regions. In the simulation, tropical reflectivity based on the TUC fraction assumes a primary role in determining the TUCRE. Accurate estimate of the TUCRE requires careful prescriptions according to actual satellite observations. We use the extent of TUC fraction and reflectivity obtained from 18 years (2003–2020) of satellite data on daily MODIS cloud properties. Our results show that the estimated net TUCRE ranges from 0.19 to 0.33 K/%, with a higher TUC fraction leading to higher temperatures (a warming effect) in the climate system. This means that a longwave TUCRE dominates over a shortwave TUCRE. When upper- and lower-level clouds interplay in the model, the range of the TUCRE was greater with a combination of two cloud layers, although all values were positive. The TUCRE is greater by 0.22 to 0.40 K/% when upper- and lower-level clouds are negatively coupled, because the Earth warms due to a decline in the reflectance of solar radiation. When upper- and lower-level clouds are positively coupled, the TUCRE is lower by 0.14 to 0.30 K/%, as less radiation reaches the Earth through combined cloud layers. Finally, we test the sensitivity of the TUCRE with five TUC fractions and 15 combinations of tropical reflectivity. Comparing our results with the TUCREs estimated fro

Journal article

Grimmich N, Plaschke F, Archer MO, Heyner D, Mieth JZD, Nakamura R, Sibeck DGet al., 2023,

Study of extreme magnetopause distortions under varying solar wind conditions

, JGR: Space Physics, Vol: 128, Pages: 1-22, ISSN: 2169-9402

To first order, the magnetopause (MP) is defined by a pressure balance between the solar wind and the magnetosphere. The boundary moves under the influence of varying solar wind conditions and transient foreshock phenomena, reaching unusually large and small distances from the Earth. We investigate under which solar wind conditions such extreme MP distortions occur. Therefore, we construct a database of magnetopause crossings (MPCs) observed by the THEMIS spacecraft in the years 2007 to mid-2022 using a simple Random Forest Classifier. Roughly 7% of the found crossing events deviate beyond reported errors in the stand-off distance from the Shue et al. (1998, https://doi.org/10.1029/98JA01103) MP model and thus are termed extreme distortions. We find the occurrence of these extreme events in terms of expansion or compression of the MP to be linked to different solar wind parameters, most notably to the IMF magnitude, cone angle, velocity, Alfvén Mach number and temperature. Foreshock transients like hot-flow anomalies and foreshock bubbles could be responsible for extreme magnetospheric expansions. The results should be incorporated into future magnetopause models and may be helpful for the reconstruction of the MP locations out of soft x-ray images, relevant for the upcoming SMILE mission.

Journal article

Arridge CS, Xystouris G, Cochrane C, Cohen I, DiBraccio G, Kollmann P, Lamy L, Masters A, Paty C, Solomonidou A, Stallard T, Styczinski M, Sulaiman Aet al., 2023,

Fundamental Space Physics in Uranus’ Magnetosphere

, Bulletin of the AAS

Journal article

Wimmer-Schweingruber RF, André N, Barabash S, Brandt PC, Horbury T, Iess L, Lavraud B, McNutt R, Provornikova E, Quemerais E, Wicks R, Wieser M, Wurz Pet al., 2023,

STELLA — In situ Investigations of the Very Local Interstellar Medium

, Bulletin of the AAS

Journal article

Chen L-J, Spence H, Klein K, Matthaeus W, Lavraud B, Szabo A, Roberts OW, Génot V, Verscharen D, Horbury T, Retino A, Alexandrova O, Reynolds C, Halekas J, Dors I, Arzamasskiy L, Contel OL, TenBarge J, Forsyth C, Jian L, Galvin A, Schekochihin A, Maruca BAet al., 2023,

Plasma turbulence: Challenges and next transformative steps from the perspective of multi-spacecraft measurements

, Bulletin of the AAS

Journal article

Wilson L, Goodrich K, Turner D, Cohen I, Whittlesey P, Schwartz Set al., 2023,

The necessity of accurate measurements of thermal velocity distribution functions in the solar wind

, Bulletin of the AAS

Journal article

Goodrich K, Schwartz S, III LW, Cohen I, Caspi A, Smith K, Rose R, Whittlesey P, Plaschke F, Halekas J, Hospodarsky G, Burch J, Gingell I, Chen L-J, Retino A, Khotyaintev Yet al., 2023,

The Persistent Mystery of Collisionless Shocks

, Bulletin of the AAS

Journal article

Montgomery J, Ebert R, Allegrini F, Bagenal F, Bolton S, DiBraccio G, Fuselier S, Wilson R, Masters Aet al., 2023,

Investigating the occurrence of Kelvin-Helmholtz instabilities at Jupiter’s dawn magnetopause

, Geophysical Research Letters, Vol: 50, ISSN: 0094-8276

We use the Kelvin-Helmholtz instability (KHI) condition with particle and magnetic field observations from Jovian Auroral Distributions Experiment and MAG on Juno along the dawn flank of Jupiter's magnetosphere. We identify the occurrence of magnetopause crossings that show evidence of being KH (Kelvin-Helmholtz) unstable. When estimating the k vector to be parallel to the velocity shear, we find that 25 of 62 (40%) magnetopause crossings satisfy the KHI condition. When considering the k vector of the maximum growth rate through a solid angle approach, we find that 60 of 62 (97%) events are KH unstable. This study shows evidence of KH waves at Jupiter's dawn flank, including primary drivers such as high velocity shears and changes in plasma pressure. Signatures of magnetic reconnection were also observed in ∼25% of the KH unstable crossings. We discuss these results and their implication for the prevalence of KHI at Juno's dawn magnetopause as measured by Juno.

Abstract
Cite

Journal article

Kang SM, Yu Y, Deser C, Zhang X, Kang I-S, Lee S-S, Rodgers KB, Ceppi Pet al., 2023,

Global impacts of recent Southern Ocean cooling

, Proceedings of the National Academy of Sciences, Vol: 120, Pages: 1-10, ISSN: 0027-8424

Since the beginning of the satellite era, Southern Ocean sea surface temperatures (SSTs) have cooled, despite global warming. While observed Southern Ocean cooling has previously been reported to have minimal impact on the tropical Pacific, the efficiency of this teleconnection has recently shown to be mediated by subtropical cloud feedbacks that are highly model-dependent. Here, we conduct a coupled model intercomparison of paired ensemble simulations under historical radiative forcing: one with freely evolving SSTs and the other with Southern Ocean SST anomalies constrained to follow observations. We reveal a global impact of observed Southern Ocean cooling in the model with stronger (and more realistic) cloud feedbacks, including Antarctic sea–ice expansion, southeastern tropical Pacific cooling, northward-shifted Hadley circulation, Aleutian low weakening, and North Pacific warming. Our results therefore suggest that observed Southern Ocean SST decrease might have contributed to cooler conditions in the eastern tropical Pacific in recent decades.

Journal article

Khabarova O, Balasis G, Bučík R, Eastwood JP, Erickson PJ, Treumann RAet al., 2023,

Editorial: Reviews in space physics

, Frontiers in Astronomy and Space Sciences, Vol: 10, Pages: 1-3, ISSN: 2296-987X

Journal article

Suen GHH, Owen CJ, Verscharen D, Horbury TS, Louarn P, De Marco Ret al., 2023,

Magnetic reconnection as an erosion mechanism for magnetic switchbacks

, ASTRONOMY & ASTROPHYSICS, Vol: 675, ISSN: 0004-6361

Cite
Citations: 2

Journal article

Sioulas N, Velli M, Huang Z, Shi C, Bowen TAA, Chandran BDG, Liodis I, Davis N, Bale SDD, Horbury TS, de Wit TD, Larson D, Stevens MLL, Kasper J, Owen CJJ, Case A, Pulupa M, Malaspina DMM, Livi R, Goetz K, Harvey PRR, MacDowall RJJ, Bonnell JWWet al., 2023,

On the Evolution of the Anisotropic Scaling of Magnetohydrodynamic Turbulence in the Inner Heliosphere

, ASTROPHYSICAL JOURNAL, Vol: 951, ISSN: 0004-637X

Cite
Citations: 14

Journal article

Leblanc F, Roth L, Chaufray JY, Modolo R, Galand M, Ivchenko N, Carnielli G, Baskevitch C, Oza A, Werner ALEet al., 2023,

Ganymede's atmosphere as constrained by HST/STIS observations

, Icarus, Vol: 399, ISSN: 0019-1035

A new analysis of aurora observations of Ganymede's atmosphere on the orbital leading and trailing hemispheres has been recently published by Roth et al. (2021), suggesting that water is its main constituent near noon. Here, we present two additional aurora observations of Ganymede's sub-Jovian and anti-Jovian hemispheres, which suggest a modulation of the atmospheric H2O/O2 ratio on the moon's orbital period, and analyze the orbital evolution of the atmosphere. For this, we propose a reconstruction of aurora observations based on a physical modelling of the exosphere taking into account its orbital variability (the Exospheric Global Model; Leblanc et al., 2017). The solution described in this paper agrees with Roth et al. (2021) that Ganymede's exosphere should be dominantly composed of water molecules. From Ganymede's position when its leading hemisphere is illuminated to when it is its trailing hemisphere, the column density of O2 may vary between 4.3 × 1014 and 3.6 × 1014 cm−2 whereas the H2O column density should vary between 5.6 × 1014 and 1.3 × 1015 cm−2. The water content of Ganymede's atmosphere is essentially constrained by its sublimation rate whereas the O2 component of Ganymede's atmosphere is controlled by the radiolytic yield. The other species, products of the water molecules, vary in a more complex way depending on their sources, either as ejecta from the surface and/or as product of the dissociation of the other atmospheric constituents. Electron impact on H2O and H2 molecules is shown to likely produce H Lyman-alpha emissions close to Ganymede, in addition to the observed extended Lyman-alpha corona from H resonant scattering. All these conclusions being highly dependent on our capability to accurately model the origins of the observed Ganymede auroral emissions, modelling these emissions remains poorly constrained without an accurate knowledge of the Jovian magnetospheric and Ganymede ionospheric electron popul

Journal article

Duan D, He J, Zhu X, Zhuo R, Wu Z, Nicolaou G, Huang J, Verscharen D, Yang L, Owen CJ, Fedorov A, Louarn P, Horbury TSet al., 2023,

Kinetic Features of Alpha Particles in a Pestchek-like Magnetic Reconnection Event in the Solar Wind Observed by Solar Orbiter

, ASTROPHYSICAL JOURNAL LETTERS, Vol: 952, ISSN: 2041-8205

Cite
Citations: 3

Search or filter publications

Filter by type:

Filter by year:

Results

Search results

Effect of a guide field on the turbulence like properties of magnetic reconnection

Useful Links