Publications

We examine the origin of electrons in a weakly outgassing comet, using Rosetta mission data and a 3D collisional model of electrons at a comet. We have calculated a new data set of electron-impact ionization (EII) frequency throughout the Rosetta escort phase, with measurements of the Rosetta Plasma Consortium’s Ion and Electron Sensor (RPC/IES). The EII frequency is evaluated in 15-min intervals and compared to other Rosetta data sets. EII is the dominant source of electrons at 67P away from perihelion and is highly variable (by up to three orders of magnitude). Around perihelion, EII is much less variable and less efficient than photoionization at Rosetta. Several drivers of the EII frequency are identified, including magnetic field strength and the outgassing rate. Energetic electrons are correlated to the Rosetta-upstream solar wind potential difference, confirming that the ionizing electrons are solar wind electrons accelerated by an ambipolar field. The collisional test particle model incorporates a spherically symmetric, pure water coma and all the relevant electron-neutral collision processes. Electric and magnetic fields are stationary model inputs, and are computed using a fully kinetic, collision-less Particle-in-Cell simulation. Collisional electrons are modelled at outgassing rates of Q = 1026 s−1 and Q = 1.5 × 1027 s−1. Secondary electrons are the dominant population within a weakly outgassing comet. These are produced by collisions of solar wind electrons with the neutral coma. The implications of large ion flow speed estimates at Rosetta, away from perihelion, are discussed in relation to multi-instrument studies and the new results of the EII frequency obtained in this study.

Journal article

Zomerdijk-Russell S, Masters A, Sun WJ, Fear RC, Slavin JAet al., 2023,

Does reconnection only occur at points of maximum shear on Mercury’s dayside magnetopause?

, JGR: Space Physics, Vol: 128, ISSN: 2169-9402

MESSENGER observations of large numbers of flux transfer events (FTEs) during dayside crossings of Mercury's magnetopause have shown that the highly dynamic Hermean magnetosphere is strongly driven by frequent and intense magnetic reconnection. Since FTEs are products of reconnection, study of them can reveal information about whether reconnection sites favor points of maximum shear on the magnetopause. Here, we analyze 201 FTEs formed under relatively stable upstream solar wind conditions as observed by MESSENGER during inbound magnetopause crossings. By modeling paths of these FTEs along the magnetopause, we determine the conditions and locations of the reconnection sites at which these FTEs were likely formed. The majority of these FTE formation paths were found to intersect with high-magnetic shear regions, defined as shear angles above 135°. Seven FTEs were found where the maximum shear angle possible between the reconnecting magnetic field lines was less than 80° and three of these had shear angles less than 70°, supporting the idea that very low-shear reconnection could be occurring on Mercury's dayside magnetopause under this global-scale picture of magnetic reconnection. Additionally, for the FTEs formed under these low-shear reconnection conditions, tracing a dominant X-line connecting points of maximum shear along the magnetopause that passes through a region of very low-shear may be difficult to justify, implying reconnection could be occurring anywhere along Mercury's magnetopause and may not be confined to points of maximum shear.

Journal article

Mozer FS, Agapitov O, Bale SD, Livi R, Romeo O, Sauer K, Vasko IY, Verniero Jet al., 2023,

Density Enhancement Streams in The Solar Wind

, ASTROPHYSICAL JOURNAL LETTERS, Vol: 957, ISSN: 2041-8205

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Journal article

Trotta D, Horbury TS, Lario D, Vainio R, Dresing N, Dimmock A, Giacalone J, Hietala H, Wimmer-Schweingruber RF, Berger L, Yang Let al., 2023,

Irregular Proton Injection to High Energies at Interplanetary Shocks

, The Astrophysical Journal Letters, Vol: 957, Pages: L13-L13, ISSN: 2041-8205

<jats:title>Abstract</jats:title> <jats:p>How thermal particles are accelerated to suprathermal energies is an unsolved issue, crucial for many astrophysical systems. We report novel observations of irregular, dispersive enhancements of the suprathermal particle population upstream of a high-Mach-number interplanetary shock. We interpret the observed behavior as irregular “injections” of suprathermal particles resulting from shock front irregularities. Our findings, directly compared to self-consistent simulation results, provide important insights for the study of remote astrophysical systems where shock structuring is often neglected.</jats:p>

Journal article

Guilbert-Lepoutre A, Benseguane S, Martinien L, Lasue J, Besse S, Grieger B, Beth Aet al., 2023,

Pits on Jupiter-family comets and the age of cometary surfaces

, The Planetary Science Journal, Vol: 4, ISSN: 2632-3338

Large and deep depressions, also known as pits, are observed at the surface of all Jupiter-family comets (JFCs) imaged by spacecraft missions. They offer the opportunity to glimpse the subsurface characteristics of comet nuclei and study the complex interplay between surface structures and cometary activity. This work investigates the evolution of pits at the surface of 81P/Wild 2, 9P/Tempel 1, and 103P/Hartley 2, in continuation of the work by Benseguane et al. on 67P/Churyumov–Gerasimenko. Pits are selected across the surface of each nucleus, and high-resolution shape models are used to compute the energy they receive. A thermal evolution model is applied to constrain how cometary activity sustained under current illumination conditions could modify them. Similar to what was found for 67P, we show that erosion resulting from water-driven activity is primarily controlled by seasonal patterns that are unique to each comet as a consequence of their shape and rotational properties. However, progressive erosion sustained after multiple perihelion passages is not able to carve any of the observed pits. Instead, cometary activity tends to erase sharp morphological features; they become wider and shallower over time. Our results reinforce the evolutionary sequence evidenced from independent measurables to transform "young" cometary surfaces, with sharp surface topography prone to outbursts, into "old" cometary surfaces. Finally, we suggest that the mechanism at the origin of the pits on JFCs should be able to carve these structures in a region of the solar system where water ice does not sublimate; the Centaur phase thus appears critical to understand JFC surface properties.

Book chapter

Cargill P, 2023,

Sydney Chapman

, Oxford's Sedleian Professors of Natural Philosophy, Editors: Hollings, McCartney, Publisher: Oxford University Press, Pages: 157-176, ISBN: 9780192843210

Sydney Chapman FRS was the Sedleian professor between 1946 and 1953. He was also one of the outstanding geophysicists of the twentieth century. His achievements cover a wide range of topics and include pioneering theory of transport in non-uniform gases, the first proposal of the nature of the ozone layer, and a comprehensive early theory of the nature of geomagnetic storms. The last of these forms the foundation of present-day studies of the Earth’s magnetosphere, and the impact of solar activity on society, referred to as space weather.

Journal article

Horner G, Gryspeerdt E, 2023,

The evolution of deep convective systems and their associated cirrus outflows

, Atmospheric Chemistry and Physics, Vol: 23, Pages: 14239-14253, ISSN: 1680-7316

Tropical deep convective clouds, particularly their large cirrus outflows, play an important role in modulating the energy balance of the Earth’s atmosphere. Whilst the cores of these deep convective clouds have a significant shortwave (SW) cooling effect, they dissipate quickly. Conversely, the thin cirrus that flow from these cores can persist for days after the core has dissipated, reaching hundreds of kilometers in extent. These thin cirrus have a potential for large warming in the tropics. Understanding the evolution of these clouds and how they change in response to anthropogenic emissions is therefore important to understand past and future climate change.This work uses a novel approach to investigate the evolution of tropical convective clouds by introducing the concept of ‘Time Since Convection’ (TSC). This is used to build a composite picture of the lifecycle of deep convection, from anvil cirrus to thin detrained cirrus. Cloud properties are a strong function of time since convection, showing decreases in the optical thickness, cloud top height, and cloud fraction over time. After an initial dissipation of the convective core, changes in thin cirrus cloud amount were seen beyond 200 hours from convection.Finally, in the initial stages of convection there was a large net negative cloud radiative effect (CRE). However, once the convective core had dissipated after 6–12 hours, the sign of the CRE flipped, and there was a sustained net warming CRE beyond 120 hours from the convective event. Changes are present in the cloud properties long after the main convective activities have dissipated, signalling the need to continue further analysis at longer time scales than previously studied.

Journal article

Salvi P, Gregory JM, Ceppi P, 2023,

Time‐evolving radiative feedbacks in the historical period

, Journal of Geophysical Research: Atmospheres, Vol: 128, ISSN: 2169-8996

We investigate the time-dependence of radiative feedback in the historical period (since the late 19th century), by analyzing experiments using coupled atmosphere–ocean climate models with historical greenhouse gas, anthropogenic aerosol, and natural forcings, each separately. We find that radiative feedback depends on forcing agent, primarily through the effect of cloud on shortwave radiation, because the various forcings cause different changes in global-mean tropospheric stability per degree of global-mean temperature change. The large time-variation of historical feedback driven by observed sea surface temperature change alone, with no forcing agents, is also consistent with tropospheric stability change, and differs from the similarly large and significant historical time-variation of feedback that is simulated in response to all forcing agents together. We show that the latter results from the varying relative sizes of individual forcings. We highlight that volcanic forcing is especially important for understanding the time-variation, because it stimulates particularly strong feedbacks that tend to reduce effective climate sensitivity. We relate this to stability changes due to enhanced surface temperature response in the Indo-Pacific warm pool.

Journal article

Rosu I-A, Grillakis M, Papadopoulos A, Agop M, Voulgarakis Aet al., 2024,

Fractal and Spectral Analysis of Recent Wildfire Scars in Greece

, FIRE TECHNOLOGY, ISSN: 0015-2684

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Journal article

George H, Malaspina DM, Goodrich K, Ma Y, Ramstad R, Conner D, Bale SD, Curry Set al., 2023,

Non-Lightning-Generated Whistler Waves in Near-Venus Space

, GEOPHYSICAL RESEARCH LETTERS, Vol: 50, ISSN: 0094-8276

Journal article

Blasl KA, Nakamura TKM, Nakamura R, Settino A, Hasegawa H, Voeroes Z, Hosner M, Schmid D, Volwerk M, Roberts OW, Panov E, Liu Y-H, Plaschke F, Stawarz JE, Holmes JCet al., 2023,

Electron-Scale Reconnecting Current Sheet Formed Within the Lower-Hybrid Wave-Active Region of Kelvin-Helmholtz Waves

, GEOPHYSICAL RESEARCH LETTERS, Vol: 50, ISSN: 0094-8276

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Journal article

Shi P, Scime EE, Barbhuiya MH, Cassak PA, Adhikari S, Swisdak M, Stawarz JEet al., 2023,

Using Direct Laboratory Measurements of Electron Temperature Anisotropy to Identify the Heating Mechanism in Electron-Only Guide Field Magnetic Reconnection

, PHYSICAL REVIEW LETTERS, Vol: 131, ISSN: 0031-9007

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Conference paper

Zhang Z, Desai R, Shebanits O, Miyake Y, Usui Het al., 2023,

Cassini's floating potential in Titan's ionosphere: 3-D particle-in-cell simulations

, URSI GASS 2023, Publisher: IEEE, Pages: 1-4

Accurate determination of Cassini’s spacecraft potential in Titan’s ionosphere is important for interpreting measurements by its low energy plasma instruments. Estimates of the floating potential varied significantly, however, between the various different plasma instruments. In this study we utilize 3-D particle-in-cell simulations to understand the key features of Cassini’s plasma interaction in Titan’s ionosphere. The spacecraft is observed to charge to negative potentials for all scenarios considered, and close agreement is found between the current onto the simulated Langmuir Probe and that observed in Titan’s ionosphere. These simulations are therefore shown to provide a viable technique for modeling spacecraft interacting with Titan’s dusty ionosphere.

Journal article

Goodrich K, Cohen IJ, Schwartz S, Wilson LB, Turner D, Caspi A, Smith K, Rose R, Whittlesey P, Plaschke Fet al., 2023,

The multi-point assessment of the kinematics of shocks (MAKOS)

, FRONTIERS IN ASTRONOMY AND SPACE SCIENCES, Vol: 10, ISSN: 2296-987X

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Journal article

Bandyopadhyay R, Meyer CM, Matthaeus WH, McComas DJ, Cranmer SR, Halekas JS, Huang J, Larson DE, Livi R, Rahmati A, Whittlesey PL, Stevens ML, Kasper JC, Bale SDet al., 2023,

Estimates of Proton and Electron Heating Rates Extended to the Near-Sun Environment

, ASTROPHYSICAL JOURNAL LETTERS, Vol: 955, ISSN: 2041-8205

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Journal article

Paouris E, Vourlidas A, Kouloumvakos A, Papaioannou A, Jagarlamudi VK, Horbury Tet al., 2023,

The Space Weather Context of the First Extreme Event of Solar Cycle 25, on 2022 September 5

, ASTROPHYSICAL JOURNAL, Vol: 956, ISSN: 0004-637X

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Journal article

Ala-Lahti M, Pulkkinen TI, Ruohotie J, Akhavan-Tafti M, Good SW, Kilpua EKJet al., 2023,

Multipoint Observations of the Dynamics at an ICME Sheath-Ejecta Boundary

, ASTROPHYSICAL JOURNAL, Vol: 956, ISSN: 0004-637X

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Journal article

Good SW, Rantala OK, Jylha A-SM, Chen CHK, Mostl C, Kilpua EKJet al., 2023,

Turbulence Properties of Interplanetary Coronal Mass Ejections in the Inner Heliosphere: Dependence on Proton Beta and Flux Rope Structure

, ASTROPHYSICAL JOURNAL LETTERS, Vol: 956, ISSN: 2041-8205

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Journal article

Pookkandy B, Graven H, Martin A, 2023,

Contemporary oceanic radiocarbon response to ocean circulation changes

, Climate Dynamics, Vol: 61, Pages: 3223-3235, ISSN: 0930-7575

Radiocarbon (14C) is a valuable tracer of ocean circulation, owing to its natural decay over thousands of years and to its perturbation by nuclear weapons testing in the 1950s and 1960s. Previous studies have used 14C to evaluate models or to investigate past climate change. However, the relationship between ocean 14C and ocean circulation changes over the past few decades has not been explored. Here we use an Ocean-Sea-ice model (NEMO) forced with transient or fixed atmospheric reanalysis (JRA-55-do) and atmospheric 14C and CO2 boundary conditions to investigate the effect of ocean circulation trends and variability on 14C. We find that 14C/C (∆14C) variability is generally anti-correlated with potential density variability. The areas where the largest variability occurs varies by depth: in upwelling regions at the surface, at the edges of the subtropical gyres at 300 m depth, and in Antarctic Intermediate Water and North Atlantic Deep Water at 1000 m depth. We find that trends in the Atlantic Meridional Overturning Circulation may influence trends in ∆14C in the North Atlantic. In the high-variability regions the simulated variations are larger than typical ocean ∆14C measurement uncertainty of 2–5‰ suggesting that ∆14C data could provide a useful tracer of circulation changes.

Journal article

Fletcher LN, Cavalié T, Grassi D, Hueso R, Lara LM, Kaspi Y, Galanti E, Greathouse TK, Molyneux PM, Galand M, Vallat C, Witasse O, Lorente R, Hartogh P, Poulet F, Langevin Y, Palumbo P, Gladstone GR, Retherford KD, Dougherty MK, Wahlund J-E, Barabash S, Iess L, Bruzzone L, Hussmann H, Gurvits LI, Santolik O, Kolmasova I, Fischer G, Müller-Wodarg I, Piccioni G, Fouchet T, Gérard J-C, Sánchez-Lavega A, Irwin PGJ, Grodent D, Altieri F, Mura A, Drossart P, Kammer J, Giles R, Cazaux S, Jones G, Smirnova M, Lellouch E, Medvedev AS, Moreno R, Rezac L, Coustenis A, Costa Met al., 2023,

Jupiter science Enabled by ESA's Jupiter Icy Moons Explorer

, Space Science Reviews, Vol: 219, ISSN: 0038-6308

ESA's Jupiter Icy Moons Explorer (JUICE) will provide a detailed investigation of the Jovian system in the 2030s, combining a suite of state-of-the-art instruments with an orbital tour tailored to maximise observing opportunities. We review the Jupiter science enabled by the JUICE mission, building on the legacy of discoveries from the Galileo, Cassini, and Juno missions, alongside ground- and space-based observatories. We focus on remote sensing of the climate, meteorology, and chemistry of the atmosphere and auroras from the cloud-forming weather layer, through the upper troposphere, into the stratosphere and ionosphere. The Jupiter orbital tour provides a wealth of opportunities for atmospheric and auroral science: global perspectives with its near-equatorial and inclined phases, sampling all phase angles from dayside to nightside, and investigating phenomena evolving on timescales from minutes to months. The remote sensing payload spans far-UV spectroscopy (50-210 nm), visible imaging (340-1080 nm), visible/near-infrared spectroscopy (0.49-5.56 μm), and sub-millimetre sounding (near 530-625 GHz and 1067-1275 GHz). This is coupled to radio, stellar, and solar occultation opportunities to explore the atmosphere at high vertical resolution; and radio and plasma wave measurements of electric discharges in the Jovian atmosphere and auroras. Cross-disciplinary scientific investigations enable JUICE to explore coupling processes in giant planet atmospheres, to show how the atmosphere is connected to (i) the deep circulation and composition of the hydrogen-dominated interior; and (ii) to the currents and charged particle environments of the external magnetosphere. JUICE will provide a comprehensive characterisation of the atmosphere and auroras of this archetypal giant planet.

Journal article

Vuorinen L, Hietala H, Lamoury AT, Plaschke Fet al., 2023,

Solar Wind Parameters Influencing Magnetosheath Jet Formation: Low and High IMF Cone Angle Regimes

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

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Journal article

Colomban L, Agapitov OV, Krasnoselskikh V, Kretzschmar M, de Wit TD, Karbashewski S, Mozer FS, Bonnell JW, Bale S, Malaspina D, Raouafi NEet al., 2023,

Reconstruction of Polarization Properties of Whistler Waves From Two Magnetic and Two Electric Field Components: Application to Parker Solar Probe Measurements

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

Journal article

Zhou Y-J, He F, Zhang X-X, Archer MO, Lin Y, Ma H, Tian A-M, Yao Z-H, Wei Y, Ni B, Liu W, Zong Q-G, Pu Z-Yet al., 2023,

A radial standing Pc5-6 wave and its energy coupling with field line resonance within the dusk-sector magnetosphere

, JGR: Space Physics, Vol: 128, ISSN: 2169-9402

Global ultra-low frequency (ULF) oscillations are believed to play a significant role in the mass, energy, and momentum transport within the Earth's magnetosphere. In this letter, we observe a ∼1.2 mHz radial standing wave in the dusk-sector magnetosphere accompanied by the field line resonance (FLR) on 16 July 2017. The frequency estimation from the simple box model also confirms the radial standing wave. The essential characteristics of FLR are concurrently identified at the dusk-sector magnetosphere and the conjugated ground location. Further, the radial standing wave dissipates energy into upper atmosphere to enhance the local aurora by coupling itself to the FLR. The magnetospheric dominant 1.2/1.1 mHz ULF waves plausibly correspond well with the discrete ∼1 mHz magnetosheath ion dynamic pressure/velocity oscillation, suggesting this radial standing wave and FLR in the flank magnetosphere may be triggered by the solar-wind and/or magnetosheath dynamic pressure/velocity fluctuations.

Journal article

Collinson GA, Hietala H, Plaschke F, Karlsson T, Wilson LB, Archer M, Battarbee M, BlancoCano X, Bertucci C, Long D, Opher M, Sergis N, Gasque C, Liu T, Raptis S, Burne S, Frahm R, Zhang T, Futaana Yet al., 2023,

Shocklets and short large amplitude magnetic structures (SLAMS) in the high mach foreshock of Venus

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

Shocklets and short large-amplitude magnetic structures (SLAMS) are steepened magnetic fluctuations commonly found in Earth's upstream foreshock. Here we present Venus Express observations from the 26th of February 2009 establishing their existence in the steady-state foreshock of Venus, building on a past study which found SLAMS during a substantial disturbance of the induced magnetosphere. The Venusian structures were comparable to those reported near Earth. The 2 Shocklets had magnetic compression ratios of 1.23 and 1.34 with linear polarization in the spacecraft frame. The 3 SLAMS had ratios between 3.22 and 4.03, two of which with elliptical polarization in the spacecraft frame. Statistical analysis suggests SLAMS coincide with unusually high solar wind Alfvén mach-number at Venus (12.5, this event). Thus, while we establish Shocklets and SLAMS can form in the stable Venusian foreshock, they may be rarer than at Earth. We estimate a lower limit of their occurrence rate of ≳14%.

Journal article

Chatoutsidou SE, Saridaki A, Raisi L, Katsivela E, Stathopoulou P, Tsiamis G, Voulgarakis A, Lazaridis Met al., 2023,

Variations, seasonal shifts and ambient conditions affecting airborne microorganisms and particles at a southeastern Mediterranean site

, SCIENCE OF THE TOTAL ENVIRONMENT, Vol: 892, ISSN: 0048-9697

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Citations: 1

Journal article

Telloni D, Romoli M, Velli M, Zank GP, Adhikari L, Downs C, Burtovoi A, Susino R, Spadaro D, Zhao L, Liberatore A, Shi C, De Leo Y, Abbo L, Frassati F, Jerse G, Landini F, Nicolini G, Pancrazzi M, Russano G, Sasso C, Andretta V, Da Deppo V, Fineschi S, Grimani C, Heinzel P, Moses JD, Naletto G, Stangalini M, Teriaca L, Uslenghi M, Berlicki A, Bruno R, Capobianco G, Capuano GE, Casini C, Casti M, Chioetto P, Corso AJ, D'Amicis R, Fabi M, Frassetto F, Giarrusso M, Giordano S, Guglielmino SL, Magli E, Massone G, Messerotti M, Nistico G, Pelizzo MG, Reale F, Romano P, Schuehle U, Solanki SK, Straus T, Ventura R, Volpicelli CA, Zangrilli L, Zimbardo G, Zuppella P, Bale SD, Kasper JCet al., 2023,

Coronal Heating Rate in the Slow Solar Wind

, ASTROPHYSICAL JOURNAL LETTERS, Vol: 955, ISSN: 2041-8205

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The evolution of deep convective systems and their associated cirrus outflows

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