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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
    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
  • Journal article
    Good SW, Rantala OK, Jylhä AM, Chen CHK, Möstl 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

    Interplanetary coronal mass ejections (ICMEs) have low proton beta across a broad range of heliocentric distances and a magnetic flux rope structure at large scales, making them a unique environment for studying solar wind fluctuations. Power spectra of magnetic field fluctuations in 28 ICMEs observed between 0.25 and 0.95 au by Solar Orbiter and Parker Solar Probe have been examined. At large scales, the spectra were dominated by power contained in the flux ropes. Subtraction of the background flux rope fields increased the mean spectral index from −5/3 to −3/2 at kd i ≤ 10−3. Rope subtraction also revealed shorter correlation lengths in the magnetic field. The spectral index was typically near −5/3 in the inertial range at all radial distances regardless of rope subtraction and steepened to values consistently below −3 with transition to kinetic scales. The high-frequency break point terminating the inertial range evolved approximately linearly with radial distance and was closer in scale to the proton inertial length than the proton gyroscale, as expected for plasma at low proton beta. Magnetic compressibility at inertial scales did not show any significant correlation with radial distance, in contrast to the solar wind generally. In ICMEs, the distinctive spectral properties at injection scales appear mostly determined by the global flux rope structure while transition-kinetic properties are more influenced by the low proton beta; the intervening inertial range appears independent of both ICME features, indicative of a system-independent scaling of the turbulence.
  • Journal article
    Trotta D, Pezzi O, Burgess D, Preisser L, Blanco-Cano X, Kajdic P, Hietala H, Horbury TS, Vainio R, Dresing N, Retinò 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

    The complex interaction between shocks and plasma turbulence is extremely important to address crucial features of energy conversion in a broad range of astrophysical systems. We study the interaction between a supercritical, perpendicular shock and pre-existing, fully developed plasma turbulence, employing a novel combination of magnetohydrodynamic and small-scale, hybrid-kinetic simulations where a shock is propagating through a turbulent medium. The variability of the shock front in the unperturbed case and for two levels of upstream fluctuations is addressed. We find that the behaviour of shock ripples, i.e. shock surface fluctuations with short (a few ion skin depths, di) wavelengths, is modified by the presence of pre-existing turbulence, which also induces strong corrugations of the shock front at larger scales. We link this complex behaviour of the shock front and the shock downstream structuring with the proton temperature anisotropies produced in the shock-turbulence system. Finally, we put our modelling effort in the context of spacecraft observations, elucidating the role of novel cross-scale, multispacecraft measurements in resolving shock front irregularities at different scales. These results are relevant for a broad range of astrophysical systems characterized by the presence of shock waves interacting with plasma turbulence.
  • 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

    The coronal mass ejection (CME) on 2022 September 5 was the fastest CME yet observed and measured in situ by a spacecraft inside the corona (0.06 au for the Parker Solar Probe). Here we assess the significance of this event for space weather studies by analyzing the source region characteristics and its temporal evolution via a magnetic complexity index. We also examine the kinematics and energetics of the CME. We find that it was a very fast and massive event, with a speed greater than 2200 km s−1 and a mass of 2 × 1016 g. Consequently, this is within the top 1% of all CMEs observed by SOHO/LASCO since 1996. It is therefore natural to ask, “What if this CME was an Earth-directed one?” To answer this question, we put the CME and the associated flare properties in the context of similar previous extreme events (namely, the 2012 July 23 and 2012 March 7 eruptions), discussing the possibility that these trigger a solar energetic particle (SEP) event. We find that 2022 September 5 could have resulted in a high-energy SEP event. We also estimate the transit time and speed of the CME and calculate the likely Dst variations if this was an Earth-directed event.
  • 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

    A central problem of space plasma physics is how protons and electrons are heated in a turbulent, magnetized plasma. The differential heating of charged species due to dissipation of turbulent fluctuations plays a key role in solar wind evolution. Measurements from previous heliophysics missions have provided estimates of proton and electron heating rates beyond 0.27 au. Using Parker Solar Probe (PSP) data accumulated during the first 10 encounters, we extend the evaluation of the individual rates of heat deposition for protons and electrons to a distance of 0.063 au (13.5 Re) in the newly formed solar wind. The PSP data in the near-Sun environment show different behavior of the electron heat conduction flux from what was predicted from previous fits to Helios and Ulysses data. Consequently, the empirically derived proton and electron heating rates exhibit significantly different behavior than previous reports, with the proton heating becoming increasingly dominant over electron heating at decreasing heliocentric distances. We find that the protons receive about 80% of the total plasma heating at ≈13 Re, slightly higher than the near-Earth values. This empirically derived heating partition between protons and electrons will help to constrain theoretical models of solar wind heating.
  • 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
    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
  • 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
    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

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