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  • 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
  • Journal article
    Telloni D, Romoli M, Velli M, Zank GP, Adhikari L, Zhao L, Downs C, Halekas JS, Verniero JL, Mcmanus MD, Shi C, Burtovoi A, Susino R, Spadaro D, Liberatore A, Antonucci E, 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, Bale SD, Kasper JCet al., 2023,

    Energy Budget in the Solar Corona

    , ASTROPHYSICAL JOURNAL, Vol: 954, ISSN: 0004-637X
  • 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

    Earth’s orbit and rotation produces systematic variations in geomagnetic activity, most notably via the changing orientation of the dayside magnetospheric magnetic field with respect to the heliospheric magnetic field (HMF). Aside from these geometric effects, it is generally assumed that the solar wind in near-Earth is uniformly sampled. But systematic changes in the intrinsic solar wind conditions in near-Earth space could arise due to the annual variations in Earth heliocentric distance and heliographic latitude. In this study, we use 24 years of Advanced Composition Explorer data to investigate the annual variations in the scalar properties of the solar wind, namely the solar wind proton density, the radial solar wind speed and the HMF intensity. All parameters do show some degree of systematic annual variation, with amplitudes of around 10 to 20%. For HMF intensity, the variation is in phase with the Earth’s heliocentric distance variation, and scaling observations for distance largely explains the observed variation. For proton density and solar wind speed, however, the phase of the annual variation is inconsistent with Earth’s heliocentric distance. Instead, we attribute the variations in speed and density to Earth’s heliographic latitude variation and systematic sampling of higher speed solar wind at higher latitudes. Indeed, these annual variations are most strongly ordered at solar minimum. Conversely, combining scalar solar wind parameters to produce estimates of dynamic pressure and potential power input to the magnetosphere results in solar maximum exhibiting a greater annual variation, with an amplitude of around 40%. This suggests Earth’s position in the heliosphere makes a significant contribution to annual variations in space weather, in addition to the already well-studied geometric effects.

  • Journal article
    Huang J, Kasper JC, Larson DE, Mcmanus MD, Whittlesey P, Livi R, Rahmati A, Romeo O, Liu M, Jian LK, Verniero JL, Velli M, Badman ST, Rivera YJ, Niembro T, Paulson K, Stevens M, Case AW, Bowen TA, Pulupa M, Bale SD, Halekas JSet al., 2023,

    The Temperature, Electron, and Pressure Characteristics of Switchbacks: Parker Solar Probe Observations

    , ASTROPHYSICAL JOURNAL, Vol: 954, ISSN: 0004-637X
  • Journal article
    Bessho N, Chen L-J, Hesse M, Ng J, Wilson LB, Stawarz JEet al., 2023,

    Electron Acceleration and Heating during Magnetic Reconnection in the Earth's Quasi-parallel Bow Shock

    , ASTROPHYSICAL JOURNAL, Vol: 954, ISSN: 0004-637X
  • Journal article
    Romeo OM, Braga CR, Badman ST, Larson DE, Stevens ML, Huang J, Phan T, Rahmati A, Livi R, Alnussirat ST, Whittlesey PL, Szabo A, Klein KG, Niembro-Hernandez T, Paulson K, Verniero JL, Lario D, Raouafi NE, Ervin T, Kasper J, Pulupa M, Bale SD, Linton MGet al., 2023,

    Near-Sun In Situ and Remote-sensing Observations of a Coronal Mass Ejection and its Effect on the Heliospheric Current Sheet

    , ASTROPHYSICAL JOURNAL, Vol: 954, ISSN: 0004-637X
  • Journal article
    Jebaraj IC, Krasnoselskikh V, Pulupa M, Magdalenic J, Bale SDet al., 2023,

    Fundamental-Harmonic Pairs of Interplanetary Type III Radio Bursts

    , ASTROPHYSICAL JOURNAL LETTERS, Vol: 955, ISSN: 2041-8205
  • 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
  • Journal article
    Alnussirat ST, Livi R, Larson DE, Rahmati A, Whittlesey PL, Romeo O, Badman ST, Buitrago-Casas M, Oliveros JCM, Pulupa M, Bale SD, Huang J, Verniero J, Raouafi N, Mitchell D, Mccomas DJ, Hill M, Cohen Cet al., 2023,

    Dispersive Suprathermal Ion Events Observed by the Parker Solar Probe Mission

    , ASTROPHYSICAL JOURNAL LETTERS, Vol: 954, ISSN: 2041-8205
  • Journal article
    Basar G, Ozturk IK, Erdogan H, Bingol D, Guzelcimen F, Kroger S, Windholz L, Pickering JC, Basar Get al., 2023,

    New even parity fine structure energy levels of atomic vanadium

    , SPECTROCHIMICA ACTA PART B-ATOMIC SPECTROSCOPY, Vol: 207, ISSN: 0584-8547
  • Journal article
    Boucher O, Bellouin N, Clark H, Gryspeerdt E, Karadayi Jet al., 2023,

    Comparison of actual and time-optimized flight trajectories in the context of the in-service aircraft for a global observing system (IAGOS) programme

    , Aerospace, Vol: 10, ISSN: 2226-4310

    Airlines optimize flight trajectories in order to minimize their operational costs, of which fuel consumption is a large contributor. It is known that flight trajectories are not fuel-optimal because of airspace congestion and restrictions, safety regulations, bad weather and other operational constraints. However, the extent to which trajectories are not fuel-optimal (and therefore CO2-optimal) is not well known. In this study, we present two methods for optimizing the flight cruising time by taking best advantage of the wind pattern at a given flight level and for constant airspeed. We test these methods against actual flight trajectories recorded under the In-service Aircraft for a Global Observing System (IAGOS) programme. One method is more robust than the other (computationally faster) method, but when successful, the two methods agree very well with each other, with optima generally within the order of 0.1%. The IAGOS actual cruising trajectories are on average 1% longer than the computed optimal for the transatlantic route, which leaves little room for improvement given that by construction the actual trajectory cannot be better than our optimum. The average degree of non-optimality is larger for some other routes and can be up to 10%. On some routes, there are also outlier flights that are not well optimized; however, the reason for this is not known.

  • Journal article
    Kang SM, Ceppi P, Yu Y, Kang I-Set al., 2023,

    Recent global climate feedback controlled by Southern Ocean cooling

    , Nature Geoscience, Vol: 16, Pages: 775-780, ISSN: 1752-0894

    The magnitude of global warming is controlled by climate feedbacks associated with various aspects of the climate system, such as clouds. The global climate feedback is the net effect of these feedbacks, and its temporal evolution is thought to depend on the tropical Pacific sea surface temperature pattern. However, current coupled climate models fail to simulate the pattern observed in the Pacific between 1979 and 2013 and its associated anomalously negative feedback. Here we demonstrate a mechanism whereby the Southern Ocean controls the global climate feedback. Using climate model experiments in which Southern Ocean sea surface temperatures are restored to observations, we show that accounting for recent Southern Ocean cooling—which is absent in coupled climate models—halves the bias in the global climate feedback by removing the cloud component bias. This global impact is mediated by a teleconnection to the Southeast Pacific, where remote sea surface temperature anomalies cause a strong stratocumulus cloud feedback. We propose that this Southern Ocean-driven pattern effect is underestimated in most climate models, owing to an overly weak stratocumulus cloud feedback. Addressing this bias may shift climate sensitivities to higher values than currently simulated as the Southern Ocean undergoes accelerated warming in future projections.

  • 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
    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
    Daei F, Pomoell J, Price DJ, Kumari A, Good S, Kilpua EKJet al., 2023,

    Modeling the formation and eruption of coronal structures by linking data-driven magnetofrictional and MHD simulations for AR 12673⋆

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

  • 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
  • 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
    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
  • Journal article
    Zimbardo G, Ying B, Nisticò G, Feng L, Rodríguez-García L, Panasenco O, Andretta V, Banerjee D, Bemporad A, De Leo Y, Franci L, Frassati F, Habbal S, Long D, Magdalenic J, Mancuso S, Naletto G, Perri S, Romoli M, Spadaro D, Stangalini M, Strachan L, Susino R, Vainio R, Velli M, Cohen CMS, Giacalone J, Shen M, Telloni D, Abbo L, Burtovoi A, Jerse G, Landini F, Nicolini G, Pancrazzi M, Russano G, Sasso C, Uslenghi Met al., 2023,

    A high-latitude coronal mass ejection observed by a constellation of coronagraphs: Solar Orbiter/Metis, STEREO-A/COR2, and SOHO/LASCO

    , Astronomy and Astrophysics, Vol: 676, ISSN: 0004-6361

    Context. A few days before the first perihelion of the Solar Orbiter nominal mission, which occurred on 2022 March 26, the Metis coronagraph on board Solar Orbiter detected a coronal mass ejection (CME) that was moving away from the far side of the Sun (with respect to Solar Orbiter) at high northern latitudes. The eruption was also seen by other spacecraft, in particular, by STEREO-A, which was in quadrature configuration with Solar Orbiter. Aims. We analyse the different views of the CME by a constellation of spacecraft with the purpose to determine the speed and acceleration of the CME, and to identify the source region of the CME. Methods. Considering the positions of various spacecraft on 2022 March 22, this CME happened to be within the field of view of STEREO-A/SECCHI, and it was visible over the limb from SOHO/LASCO. We present the results of the 3D reconstruction of the CME based on the graduated cylindrical shell model and of the identification of the possible origin of the CME using extreme-ultraviolet (EUV) observations by Solar Orbiter/EUI, STEREO-A/EUVI, and SDO/AIA. The observations in EUV are compared with the coronal magnetic structure obtained by the potential field source surface method. Results. The 3D reconstruction of the CME derives a central latitude of 29 N, a Stonyhurst longitude of 125, and an average radial speed at the apex of 322 ± 33 km s1 between 4 and 13 RȮ, which is probably not high enough to generate a shock wave. The estimated average acceleration of the CME is 16 ± 11 m s2 in the same range of distances from the Sun. This CME may be associated with the disappearance of a coronal cloud prominence, which is seen in the EUV by STEREO-A/EUVI and SDO/AIA, and is also associated with rapidly evolving emerging magnetic flux.

  • 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
    Roberts OW, Voeroes Z, Torkar K, Stawarz J, Bandyopadhyay R, Gershman DJ, Narita Y, Kieokaew R, Lavraud B, Klein K, Yang Y, Nakamura R, Chasapis A, Matthaeus WHet al., 2023,

    Estimation of the Error in the Calculation of the Pressure-Strain Term: Application in the Terrestrial Magnetosphere

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 128, ISSN: 2169-9380
  • Journal article
    Usanova ME, Ergun RE, Stawarz JE, 2023,

    Ion Energization by Turbulent Electric Fields in Fast Earthward Flows and Its Implications for the Dynamics of the Inner Magnetosphere

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

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