Publications

Conference paper

Beth A, Galand M, Modolo R, Leblanc F, Jia Xet al., 2024,

Impact of ion-neutral chemistry on Ganymede's ionosphere

<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'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+. As we showed in [1] by means of a test particle model, the ion composition during most flybys was a priori dominated by H2+and O2+. However, during Juno's flyby of Ganymede, plasma data revealed the additional presence of H3+ that may only stem from ion neutral reactions between H2 and H2+.&#160;&#160;We have updated our test particle model to account for these ion-neutral collisions of which &#160;H2 + H2+. We show how it modifies the ion composition compared with [1] and assess the role of these collisions in the production of new ion species within Ganymede's exo-ionosphere. This will help to interpret plasma observations made by Juno and in the future by JUICE around Ganymede.&#160;[1] Beth et al., EGU24, https://doi.org/10.5194/egusphere-egu24-11772, 2024</jats:p>

Conference paper

Lewis Z, Stephenson P, Kallio E, Galand M, Beth Aet al., 2024,

Evolution of the ion dynamics at comet 67P during the escort phase

<jats:p>Comet 67P/Churyumov-Gerasimenko was escorted by the Rosetta spacecraft through a 2 year section of its 6 year orbit around the Sun. This enabled the observation of a large variation in comet outgassing and the resulting evolution of the plasma environment. The diamagnetic cavity, a region of negligible magnetic field arising from the interaction of the unmagnetised cometary plasma with the solar wind, began to be detected sporadically by the Rosetta Plasma Consortium/ Magnetometer (RPC/MAG) in April 2015 at a heliocentric distance of 1.8 au [1]. The last detections were in February 2016 at 2.4 au. Within this cavity, the flow of cometary ions has been shown to be largely radial [2]; the ions are accelerated above the neutral gas speed by an ambipolar electric field, but many newborn ions still undergo multiple ion-neutral chemical reactions before escaping [3,4]. Outside the diamagnetic cavity boundary, which is itself highly variable, the ion flow is considerably more complex, and the ambipolar electric field plays a more minor role compared to the convective electric field of the solar wind [2]. &#160;At large heliocentric distances (>2.5 au), the total plasma density observed from RPC plasma sensors is well explained by a simple flux conservation model that assumes the ions travel radially away from the nucleus at speed close to that of neutrals [5,6]. However, closer to perihelion and once the diamagnetic cavity has formed, such an approach does not hold [7]. We aim to better understand this transition, the driver of ions' acceleration, and the role that the diamagnetic cavity plays.In this study, we explore the varying ion dynamics both in the presence (e.g. during high outgassing activity) and absence (low outgassing activity) of a diamagnetic cavity. Electric and magnetic fields from hybrid simulations of the cometary environment are used to drive a 3D test particle model of the cometary ions for a range of comet activity levels.

Journal article

Ervin T, Bale SD, Badman ST, Rivera YJ, Romeo O, Huang J, Riley P, Bowen TA, Lepri ST, Dewey RMet al., 2024,

Compositional Metrics of Fast and Slow Alfvénic Solar Wind Emerging from Coronal Holes and Their Boundaries

, ASTROPHYSICAL JOURNAL, Vol: 969, ISSN: 0004-637X

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Journal article

Schwadron NA, Bale SD, Bonnell J, Case A, Shen M, Christian ER, Cohen CMS, Davis AJ, Desai MI, Goetz K, Giacalone J, Hill ME, Kasper JC, Korreck K, Larson D, Livi R, Lim T, Leske RA, Malandraki O, Malaspina D, Matthaeus WH, McComas DJ, McNutt RL, Mewaldt RA, Mitchell DG, Niehof JT, Pulupa M, Pecora F, Rankin JS, Smith C, Stone EC, Szalay JR, Vourlidas A, Wiedenbeck ME, Whittlesey Pet al., 2024,

Parker Solar Probe Observations of Energetic Particles in the Flank of a Coronal Mass Ejection Close to the Sun

, ASTROPHYSICAL JOURNAL, Vol: 970, ISSN: 0004-637X

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Journal article

Mathews J, Czaja A, 2024,

Oceanic maintenance of atmospheric blocking in wintertime in the North Atlantic

, Climate Dynamics, Vol: 62, ISSN: 0930-7575

The connection between atmospheric blocking over the North Atlantic and the diabatic influence of the Gulf Stream is investigated using potential vorticity and moist potential vorticity diagnostics in the ERA5 reanalysis data set during wintertime (1979 - 2020). In line with previous research, the reliance atmospheric blocking has on turbulent heat fluxes over the Gulf Stream and its extension, for induction and maintenance, is shown to be significant. The air-sea heat flux generates negative potential vorticity air masses in the atmospheric boundary layer. These air masses subsequently contribute to the block’s negative potential vorticity anomaly at upper levels through ascending motion in the warm conveyor belt. It is shown that the block’s size and frequency partially depends on oceanic preconditioning via anomalous oceanic heat transport and heat content, prior to the blocking event, both of which allow for stronger turbulent heat fluxes. It is further hypothesized that the block feeds back positively on itself through the advection of cold dry air over the Gulf Stream, sustaining this air-sea interaction. This in turn decreases ocean heat content, eventually halting this air-sea interaction and severing the atmospheric block from its maintenance pathway.

Journal article

Lester JG, Graven HD, Khatiwala S, McNichol APet al., 2024,

Changes in Oceanic Radiocarbon and CFCs Since the 1990s

, JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, Vol: 129, ISSN: 2169-9275

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Journal article

Wilson Kemsley S, Ceppi P, Andersen H, Cermak J, Stier P, Nowack Pet al., 2024,

A systematic evaluation of high-cloud controlling factors

, Atmospheric Chemistry and Physics, Vol: 24, Pages: 8295-8316, ISSN: 1680-7316

Clouds strongly modulate the top-of-the-atmosphere energy budget and are a major source of uncertainty in climate projections. “Cloud controlling factor” (CCF) analysis derives relationships between large-scale meteorological drivers and cloud radiative anomalies, which can be used to constrain cloud feedback. However, the choice of meteorological CCFs is crucial for a meaningful constraint. While there is rich literature investigating ideal CCF setups for low-level clouds, there is a lack of analogous research explicitly targeting high clouds. Here, we use ridge regression to systematically evaluate the addition of five candidate CCFs to previously established core CCFs within large spatial domains to predict longwave high-cloud radiative anomalies: upper-tropospheric static stability (SUT), sub-cloud moist static energy, convective available potential energy, convective inhibition, and upper-tropospheric wind shear (ΔU300). We identify an optimal configuration for predicting high-cloud radiative anomalies that includes SUT and ΔU300 and show that spatial domain size is more important than the selection of CCFs for predictive skill. We also find an important discrepancy between the optimal domain sizes required for predicting locally and globally aggregated radiative anomalies. Finally, we scientifically interpret the ridge regression coefficients, where we show that SUT captures physical drivers of known high-cloud feedbacks and deduce that the inclusion of SUT into observational constraint frameworks may reduce uncertainty associated with changes in anvil cloud amount as a function of climate change. Therefore, we highlight SUT as an important CCF for high clouds and longwave cloud feedback.

Journal article

Acevski M, Masters A, ZomerdijkRussell S, 2024,

Asymmetry in Uranus' high energy proton radiation belt

, Geophysical Research Letters, Vol: 51, ISSN: 0094-8276

Uranus is one of the least explored planets in our solar system, it exhibits a unique magnetic field structure which was observed by NASA's Voyager 2 mission nearly 50 years ago. Notably, Uranus displays extreme magnetic field asymmetry, a feature exclusive to the icy giants. We use the Boris algorithm to investigate how high energy protons behave within this unusual magnetic field, which is motivated by Voyager 2's observation of lower-than-expected high energy proton radiation belt intensities at Uranus. When considering full drift motions of high energy protons around Uranus, the azimuthal drift velocity can vary by as much as 15% around the planet. This results in areas around Uranus where particles will be more depleted (faster drift) and other regions where there is a surplus of particles (slower drift). This could provide a partial explanation for the “weak” proton radiation belts observed by Voyager 2.

Journal article

Kasoar M, Perkins O, Millington JDA, Mistry J, Smith Cet al., 2024,

Model fires, not ignitions: capturing the human dimension of global fire regimes

, Cell Reports Sustainability, Vol: 1, ISSN: 2949-7906

Fire regimes are intrinsically shaped by humans, but current global fire models do not reflect the diverse objectives humans have for managing fire. With new data sources and collaboration across disciplines, an improved understanding of human influences on fire regimes is increasingly possible and essential to represent.

Journal article

Mülmenstädt J, Gryspeerdt E, Dipu S, Quaas J, Ackerman AS, Fridlind AM, Tornow F, Bauer SE, Gettelman A, Ming Y, Zheng Y, Ma P-L, Wang H, Zhang K, Christensen MW, Varble AC, Leung LR, Liu X, Neubauer D, Partridge DG, Stier P, Takemura Tet al., 2024,

General circulation models simulate negative liquid water path–droplet number correlations, but anthropogenic aerosols still increase simulated liquid water path

, Atmospheric Chemistry and Physics, Vol: 24, Pages: 7331-7345, ISSN: 1680-7316

General circulation models' (GCMs) estimates of the liquid water path adjustment to anthropogenic aerosol emissions differ in sign from other lines of evidence. This reduces confidence in estimates of the effective radiative forcing of the climate by aerosol–cloud interactions (ERFaci). The discrepancy is thought to stem in part from GCMs' inability to represent the turbulence–microphysics interactions in cloud-top entrainment, a mechanism that leads to a reduction in liquid water in response to an anthropogenic increase in aerosols. In the real atmosphere, enhanced cloud-top entrainment is thought to be the dominant adjustment mechanism for liquid water path, weakening the overall ERFaci. We show that the latest generation of GCMs includes models that produce a negative correlation between the present-day cloud droplet number and liquid water path, a key piece of observational evidence supporting liquid water path reduction by anthropogenic aerosols and one that earlier-generation GCMs could not reproduce. However, even in GCMs with this negative correlation, the increase in anthropogenic aerosols from preindustrial to present-day values still leads to an increase in the simulated liquid water path due to the parameterized precipitation suppression mechanism. This adds to the evidence that correlations in the present-day climate are not necessarily causal. We investigate sources of confounding to explain the noncausal correlation between liquid water path and droplet number. These results are a reminder that assessments of climate parameters based on multiple lines of evidence must carefully consider the complementary strengths of different lines when the lines disagree.

Journal article

Graven HD, Warren H, Gibbs HK, Khatiwala S, Koven C, Lester J, Levin I, Spawn-Lee SA, Wieder Wet al., 2024,

Bomb radiocarbon evidence for strong global carbon uptake and turnover in terrestrial vegetation

, Science, Vol: 384, Pages: 1335-1339, ISSN: 0036-8075

Vegetation and soils are taking up approximately 30% of anthropogenic carbon dioxide emissions because of small imbalances in large gross carbon exchanges from productivity and turnover that are poorly constrained. We combined a new budget of radiocarbon produced by nuclear bomb testing in the 1960s with model simulations to evaluate carbon cycling in terrestrial vegetation. We found that most state-of-the-art vegetation models used in the Coupled Model Intercomparison Project underestimated the radiocarbon accumulation in vegetation biomass. Our findings, combined with constraints on vegetation carbon stocks and productivity trends, imply that net primary productivity is likely at least 80 petagrams of carbon per year presently, compared with the 43 to 76 petagrams per year predicted by current models. Storage of anthropogenic carbon in terrestrial vegetation is likely more short-lived and vulnerable than previously predicted.

Journal article

Amtmann C, Pollinger A, Ellmeier M, Dougherty M, Brown P, Lammegger R, Betzler A, Agu M, Hagen C, Jernej I, Wilfinger J, Baughen R, Strickland A, Magnes Wet al., 2024,

Accuracy of the scalar magnetometer aboard ESA's JUICE mission

, GEOSCIENTIFIC INSTRUMENTATION METHODS AND DATA SYSTEMS, Vol: 13, Pages: 177-191, ISSN: 2193-0856

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Journal article

Kang H, Choi Y-S, Jiang JH, 2024,

Factors determining tropical upper-level cloud radiative effect in the radiative-convective equilibrium framework

, Scientific Reports, Vol: 14

<jats:title>Abstract</jats:title> <jats:p>Investigation of the major factors determining tropical upper-level cloud radiative effect (TUCRE) is crucial for understanding cloud feedback mechanisms. We examined the TUCRE inferred from the outputs of historical runs and AMIP runs from CMIP6 models employing a radiative-convective equilibrium (RCE). In this study, we incorporated the RCE model configurations of atmospheric dynamics and thermodynamics from the climate models, while simplifying the intricate systems. Using the RCE model, we adjusted the global mean surface temperature to achieve energy balance, considering variations in tropical cloud fraction, regional reflectivity, and emission temperature corresponding to each climate model. Subsequently, TUCRE was calculated as a unit of K/%, representing the change in global mean surface temperature (K) in response to an increment in the tropical upper-level clouds (%). Our RCE model simulation indicates that the major factors determining the TUCRE are the emission temperatures of tropical moist-cloudy and moist-clear regions, as well as the fraction of tropical upper-level clouds. The higher determination coefficients between TUCRE and both the emission temperature of tropical moist regions and the upper-level cloud fraction are attributable to their contribution to the trapping effect on the outgoing longwave radiations, which predominantly determines TUCRE. Consequently, the results of this study underscore the importance of accurately representing the upper-level cloud fraction and emission temperature in tropical moist regions to enhance the representation of TUCRE in climate models.</jats:p>

Journal article

Hou C, Rouillard AP, He J, Gannouni B, Reville V, Louarn P, Fedorov A, Prech L, Owen CJ, Verscharen D, D'Amicis R, Sorriso-Valvo L, Fargette N, Coburn J, Genot V, Raines JM, Bruno R, Livi S, Lavraud B, Andre N, Fruit G, Kieokaew R, Plotnikov I, Penou E, Barthe A, Kataria D, Berthomier M, Allegrini F, Fortunato V, Mele G, Horbury Tet al., 2024,

Connecting Solar Wind Velocity Spikes Measured by Solar Orbiter and Coronal Brightenings Observed by SDO

, ASTROPHYSICAL JOURNAL LETTERS, Vol: 968, ISSN: 2041-8205

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Journal article

Jebaraj IC, Agapitov O, Krasnoselskikh V, Vuorinen L, Gedalin M, Choi K-E, Palmerio E, Wijsen N, Dresing N, Cohen C, Kouloumvakos A, Balikhin M, Vainio R, Kilpua E, Afanasiev A, Verniero J, Mitchell JG, Trotta D, Hill M, Raouafi N, Bale SDet al., 2024,

Acceleration of Electrons and Ions by an "Almost" Astrophysical Shock in the Heliosphere

, ASTROPHYSICAL JOURNAL LETTERS, Vol: 968, ISSN: 2041-8205

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Journal article

Agiwal O, Cao H, Hsu H-W, Moore L, Sulaiman AH, O'Donoghue J, Dougherty MKet al., 2024,

Current Events at Saturn: Ring-Planet Electromagnetic Coupling

, PLANETARY SCIENCE JOURNAL, Vol: 5

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Journal article

Krupar V, Kruparova O, Szabo A, Wilson III LB, Nemec F, Santolik O, Pulupa M, Issautier K, Bale SD, Maksimovic Met al., 2024,

Radial Variations in Solar Type III Radio Bursts

, ASTROPHYSICAL JOURNAL LETTERS, Vol: 967, ISSN: 2041-8205

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Journal article

Vasko IY, Mozer FS, Bowen T, Verniero J, An X, Artemyev AV, Bale SD, Bonnell JW, Halekas J, Kuzichev IVet al., 2024,

Resonance of Low-frequency Electromagnetic and Ion-sound Modes in the Solar Wind

, ASTROPHYSICAL JOURNAL LETTERS, Vol: 967, ISSN: 2041-8205

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Journal article

Eastwood JP, Brown P, Magnes W, Carr CM, Agu M, Baughen R, Berghofer G, Hodgkins J, Jernej I, Moestl C, Oddy T, Strickland A, Vitkova Aet al., 2024,

The Vigil magnetometer for operational space weather services from the Sun-Earth L5 point

, Space Weather, Vol: 22, ISSN: 1539-4956

Severe space weather has the potential to cause significant socio-economic impact and it is widely accepted that mitigating this risk requires more comprehensive observations of the Sun and heliosphere, enabling more accurate forecasting of significant events with longer lead-times. In this context, it is now recognized that observations from the L5 Sun-Earth Lagrange point (both remote and in situ) would offer considerable improvements in our ability to monitor and forecast space weather. Remote sensing from L5 allows for the observation of solar features earlier than at L1, providing early monitoring of active region development, as well as tracking of interplanetary coronal mass ejections through the inner heliosphere. In situ measurements at L5 characterize the solar wind's geoeffectiveness (particularly stream interaction regions), and can also be ingested into heliospheric models, improving their performance. The Vigil space weather mission is part of the ESA Space Safety Program and will provide a real-time data stream for space weather services from L5 following its anticipated launch in the early 2030s. The interplanetary magnetic field is a key observational parameter, and here we describe the development of the Vigil magnetometer instrument for operational space weather monitoring at the L5 point. We summarize the baseline instrument capabilities, demonstrating how heritage from science missions has been leveraged to develop a low-risk, high-heritage instrument concept.

Journal article

Fuselier SA, Petrinec SM, Reiff PH, Birn J, Baker DN, Cohen IJ, Nakamura R, Sitnov MI, Stephens GK, Hwang J, Lavraud B, Moore TE, Trattner KJ, Giles BL, Gershman DJ, Toledo-Redondo S, Eastwood JPet al., 2024,

Global-scale processes and effects of magnetic reconnection on the geospace environment

, Space Science Reviews, Vol: 220, ISSN: 0038-6308

Recent multi-point measurements, in particular from the Magnetospheric Multiscale (MMS)spacecraft, have advanced the understanding of micro-scale aspects of magnetic reconnection. In addition, the MMS mission, as part of the Heliospheric System Observatory, combined with recent advances in global magnetospheric modeling, have furthered the understanding of meso- and global-scale structure and consequences of reconnection. Magneticreconnection at the dayside magnetopause and in the magnetotail are the drivers of the globalDungey cycle, a classical picture of global magnetospheric circulation. Some recent advances in the global structure and consequences of reconnection that are addressed hereinclude a detailed understanding of the location and steadiness of reconnection at the dayside magnetopause, the importance of multiple plasma sources in the global circulation, andreconnection consequences in the magnetotail. These advances notwithstanding, there areimportant questions about global reconnection that remain. These questions focus on howmultiple reconnection and reconnection variability fit into and complicate the Dungey Cyclepicture of global magnetospheric circulation.

Journal article

Choi H, Choi Y-S, Song H-J, Kang H, Kim Get al., 2024,

Potential Improvement of GK2A Clear-Sky Atmospheric Motion Vectors Using the Convolutional Neural Network Model

, Asia-Pacific Journal of Atmospheric Sciences, Vol: 60, Pages: 245-253, ISSN: 1976-7633

<jats:title>Abstract</jats:title><jats:p>In this study, we propose a new approach to improve the accuracy of the horizontal atmospheric motion vector (AMV) in cloud-free skies and its forecasting. We adapted the optical flow of the convolutional neural network (CNN) framework model using two 10-min interval infrared images at water vapor channels (centered at 6.3, 7.0, and 7.3 <jats:inline-formula><jats:alternatives><jats:tex-math>$$\mu m$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>μ</mml:mi> <mml:mi>m</mml:mi> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula>) from the Korean geostationary satellite GEO-KOMPSAT-2A (GK2A). Since all pixels had seamless AMVs calculated by CNN (CNN AMVs), we could also predict AMVs using the linear regression method. The tracking performance of the CNN-based algorithm was validated using AMVs retrieved from GK2A (GK2A AMVs) by estimating the difference between those values and the ECMWF (European Centre for Medium-Range Weather Forecasts) Reanalysis v5 (ERA5) wind data over Korea in 2022. CNN AMVs showed similar or better root-mean-square vector differences (RMSVDs) than GK2A AMVs (12.33–12.86 vs. 15.89–19.96 m/s). The RMSVDs of the forecasted AMVs were 2.74, 2.95, 3.41, and 4.79 m/s at lead times of 10, 20, 30, and 60 min, respectively. Consequently, our method showed higher accuracy for tracking motion in the production of AMVs and succeeded in forecasting AMVs. We expect that such potential improvements in computational accuracy for operational GK2A AMVs will contribute to increased accuracy when forecasting meteorological phenomena related to wind.</jats:p>

Journal article

Archer M, Pilipenko V, Li B, Sorathia K, Nakariakov V, Elsden T, Nykyri Ket al., 2024,

Magnetopause MHD surface wave theory: progress & challenges

, Frontiers in Astronomy and Space Sciences, Vol: 11, ISSN: 2296-987X

Sharp boundaries are a key feature of space plasma environments universally, with their wave-like motion (driven by pressure variations or flow shears) playing a key role in mass, momentum, and energy transfer. This review summarises magnetohydrodynamic surface wave theory with particular reference to Earth’s magnetopause, due to its mediation of the solar-terrestrial interaction. Basic analytic theory of propagating and standing surface waves within simple models are presented, highlighting many of the typically-used assumptions. We raise several conceptual challenges to understanding the nature of surface waves within a complex environment such as a magnetosphere, including the effects of magnetic topology and curvilinear geometry, plasma inhomogeneity, finite boundary width, the presence of multiple boundaries, turbulent driving, and wave nonlinearity. Approaches to gain physical insight into these challenges are suggested. We also discuss how global simulations have proven a fruitful tool in studying surface waves in more representative environments than analytic theory allows. Finally, we highlight strong interdisciplinary links with solar physics which might help the magnetospheric community. Ultimately several upcoming missions provide motivation for advancing magnetopause surface wave theory towards understanding their global role in filtering, accumulating, and guiding turbulent solar wind driving.

Journal article

Opgenoorth HJ, Robinson R, Ngwira CM, Garcia Sage K, Kuznetsova M, El Alaoui M, Boteler D, Gannon J, Weygand J, Merkin V, Nykyri K, Kosar B, Welling D, Eastwood J, Eggington J, Heyns M, Kaggwa Kwagala N, Sur D, Gjerloev Jet al., 2024,

Earth’s geomagnetic environment—progress and gaps in understanding, prediction, and impacts

, Advances in Space Research, ISSN: 0273-1177

Understanding of Earth’s geomagnetic environment is critical to mitigating the space weather impacts caused by disruptive geoelectric fields in power lines and other conductors on Earth’s surface. These impacts are the result of a chain of processes driven by the solar wind and linking Earth’s magnetosphere, ionosphere, thermosphere and Earth’s surface. Tremendous progress has been made over the last two decades in understanding the solar wind driving mechanisms, the coupling mechanisms connecting the magnetically controlled regions of near-Earth space, and the impacts of these collective processes on human technologies on Earth’s surface. Studies of solar wind drivers have been focused on understanding the responses of the geomagnetic environment to spatial and temporal variations in the solar wind associated with Coronal Mass Ejections, Corotating Interaction Regions, Interplanetary Shocks, High-Speed Streams, and other interplanetary magnetic field structures. Increasingly sophisticated numerical models are able to simulate the magnetospheric response to the solar wind forcing associated with these structures. Magnetosphere-ionosphere-thermosphere coupling remains a great challenge, although new observations and sophisticated models that can assimilate disparate data sets have improved the ability to specify the electrodynamic properties of the high latitude ionosphere. The temporal and spatial resolution needed to predict the electric fields, conductivities, and currents in the ionosphere is driving the need for further advances. These parameters are intricately tied to auroral phenomena—energy deposition due to Joule heating and precipitating particles, motions of the auroral boundary, and ion outflow. A new view of these auroral processes is emerging that focuses on small-scale structures in the magnetosphere and their ionospheric effects, which may include the rapid variations in current associated with geomagnetically indu

Conference paper

Stephenson P, Galand M, Deca J, Henri P, Carnielli Get al., 2024,

Cooling of Electrons in a Weakly Outgassing Comet

<jats:p>The plasma instruments, Mutual Impedance Probe (MIP) and Langmuir Probe (LAP), part of the Rosetta Plasma Consortium (RPC), onboard the Rosetta mission to comet 67P revealed a population of cold electrons (</jats:p>

Journal article

Provan G, Bradley T, Bunce E, Hunt G, Cowley S, Cao H, Dougherty M, Roussos E, Tao Cet al., 2024,

Saturn&#8217;s nightside ring current during Cassini&#8217;s Grand Finale

<jats:p>During Cassini&#8217;s Grand Finale proximal orbits, the spacecraft traversed the nightside magnetotail to ~21 Saturn radii. &#160;Clear signatures of Saturn&#8217;s equatorial current sheet are observed in the magnetic field data. &#160;An axisymmetric model of the ring current is fitted to these data, amended to taken into account the tilt of the current layer by solar wind forcing, its teardrop-shaped nature and the magnetotail and magnetopause fringing fields. &#160;Variations in ring current parameters are examined in relation to external driving of the magnetosphere by the solar wind, and internal driving by the two planetary period oscillations (PPOs) and compared with dawn and dayside regimes. &#160;The relative phasing of the PPOs determines the ring current&#8217;s response to solar wind conditions. During solar wind compressions when the PPOS are in antiphase, magnetospheric storms are triggered and a thick partial ring current is formed on the nightside, dominated by hot plasma injected by tail reconnection.&#160; However, during solar wind compressions when the PPOs are in phase, the magnetosphere shows only a &#8216;minor&#8217; response and a partial ring current is not observed. During solar wind rarefactions an equatorial &#8216;magnetodisc&#8217; configuration is observed in the dayside/dawn/nightside regions, with similar total currents flowing at these local times. &#160;This partial ring current should close partly via magnetopause currents and possibly via field-aligned currents into the ionosphere. &#160;During very quiet intervals of prolonged solar wind rarefaction, a thin current sheet with an enhanced current density is formed, indicative of a ring current dominated by cool, dense, Enceladus water group ions.</jats:p>

Conference paper

Stephenson P, Galand M, Deca J, Henri P, Carnielli Get al., 2024,

Forming a cold electron population at a weakly outgassing comet

<jats:p>The Rosetta Mission rendezvoused with comet 67P/Churyumov-Gerasimenko in August 2014 and escorted it for two years along its orbit. The Rosetta Plasma Consortium (RPC) was a suite of instruments, which observed the plasma environment at the spacecraft throughout the escort phase. The Mutual Impedance Probe (RPC/MIP; Wattieaux et al, 2020; Gilet et al., 2020) and Langmuir Probe (RPC/LAP; Engelhardt et al., 2018), both part of RPC, measured the presence of a cold electron population within the coma.Newly born electrons, generated by ionisation of the neutral gas, form a warm population within the coma at ~10eV. Ionisation is either through absorption of extreme ultraviolet photons or through collisions of energetic electrons with the neutral molecules. The cold electron population is formed by cooling the newly born, warm electrons via electron-neutral collisions. Assuming the radial outflow of electrons, the cold population was only expected at comet 67P close to perihelion, where outgassing rate from the nucleus was at its highest (Q > 1028 s-1). However, cold electrons were observed until the end of the Rosetta mission at 3.8au when the outgassing was weak (Q</jats:p>

Conference paper

Rothkaehl H, Andre N, Auster U, Della Corte V, Edberg N, Galand M, Henri P, De Keyser J, Kolmasova I, Morawski M, Nilsson H, Prech L, Volwerk M, Goetz C, Gunell H, Lavraud B, Rotundi A, Soucek Jet al., 2024,

Dust, Field and Plasma instrument onboard ESA&#8217;s Comet Interceptor &#160;mission

<jats:p>The main goal of ESA&#8217;s F-1 class Comet Interceptor mission is to characterise, for the first time, a long period comet; preferably a dynamically-new or an interstellar object. The main spacecraft, will have its trajectory outside of the inner coma, whereas two sub-spacecrafts will be targeted inside the inner coma, closer to the nucleus. The flyby of such a comet &#160;will offer unique multipoint measurement opportunity to study the comet's dusty and ionised environment in ways exceeding that of the previous cometary missions, including Rosetta.&#160;The Dust Field and Plasma (DFP) instruments located on both the main spacecraft A and on the sub-spacecraft B2, is a combined experiment dedicated to the in situ, multi-point study of the multi-phased ionized and dusty environment in the coma of the target and &#160;its interaction with the surrounding space environment and the Sun.&#160;The DFP instruments will be present in different configurations on the Comet Interceptor spacecraft A and B2. To enable the measurements on spacecraft A, the DFP is composed of 5 sensors; Fluxgate magnetometer DFP-FGM-A, Plasma instrument with nanodust and E-field measurements capabilities DFP-COMPLIMENT, Electron spectrometer DFP-LEES, Ion and energetic neutrals spectrometer DFP-SCIENA &#160;and Dust detector DFP-DISC. On board of spacecraft B2 the DFP is composed of 2 sensors: Fluxgate magnetometer DFP-FGM-B2 and Cometary dust detector DFP-DISC.&#160;The DFP instrument will measure magnetic field, the electric field, plasma parameters (density, temperature, speed), the distribution functions of electrons, ions and energetic neutrals, spacecraft potential, mass, number and spatial density of cometary dust particles and the dust impacts. &#160;&#160;The full set of DFP sensors will allow to model the comet plasma environment and its interaction with the solar wind. It will also allow to describe

Conference paper

Benseguane S, Guilbert-Lepoutre A, Lasue J, Leyrat C, Besse S, Beth A, Costa Sitjà M, Grieger B, Teresa Capria Met al., 2024,

A new take on the formation and evolution of circular depressions at the surface of 67P/Churyumov-Gerasimenko

<jats:p>&#160;IntroductionSome of the comets visited by spacecraft missions display some circular depressions at their surface: 81P/Wild 2 (Brownlee et al. 2004), 9P/Tempel 1 (Belton et al. 2013), 103P/Hartley 2 (Bruck Syal et al. 2013), 67P/C-G (Vincent et al. 2015). For 67P, they consist of circular holes, half holes or cliffs, with a size range of tens of meters to a few hundreds of meters (Ip et al. 2016). Owing to the high precision of the shape model obtained from the Rosetta/OSIRIS images (Preusker et al. 2015, Sierks et al. 2015), it is possible to investigate the thermal processing of 67P&#8217;s surface in relation to the formation and evolution of these features (Mousis et al. 2015, Vincent et al. 2015, Guilbert-Lepoutre et al. 2016).&#160;&#160;MethodsWe aim to investigate the formation and evolution of 67P&#8217;s circular depressions (or pits, thereafter) by thermally-induced processes (for instance sublimation and amorphous water ice crystallization) on its current orbit. In a departure from the aforementioned studies, we consider a high-resolution shape model of the nucleus, which allows to study several facets for each pit: at the bottom, and on the walls. For each facet, the complete thermal environment is considered, including self-heating and shadowing, either by neighboring facets or due to the complex global morphology of the comet. We compute the illumination, self-heating and shadowing conditions for 125k facets during a full orbit, with a time step of ~8 min, then use these conditions as an input of a 1D thermal evolution model for each facet. The model includes standard features: heat conduction, phase transitions, gas diffusion, erosion, dust mantling (De Sanctis et al. 2005, 2010, Lasue et al. 2008). Various initial setups have been considered, and many tests were conducted to assess the influence of each parameter. The behaviour of 30 circular depressions (pits, half pits and cliffs) was stud

Journal article

Cohen CMS, Leske RA, Christian ER, Cummings AC, de Nolfo GA, Desai MI, Giacalone J, Hill ME, Labrador AW, Mccomas DJ, Mcnutt RL, Mewaldt RA, Mitchell DG, Mitchell JG, Muro GD, Rankin JS, Schwadron NA, Sharma T, Shen MM, Szalay JR, Wiedenbeck ME, Xu ZG, Romeo O, Vourlidas A, Bale SD, Pulupa M, Kasper JC, Larson DE, Livi R, Whittlesey Pet al., 2024,