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  • Journal article
    Cui X, Newman S, Xu X, Andrews AE, Miller J, Lehman S, Jeong S, Zhang J, Priest C, Campos-Pineda M, Gurney KR, Graven H, Southon J, Fischer MLet al., 2019,

    Atmospheric observation-based estimation of fossil fuel CO<sub>2</sub> emissions from regions of central and southern California

    , SCIENCE OF THE TOTAL ENVIRONMENT, Vol: 664, Pages: 381-391, ISSN: 0048-9697
  • Journal article
    Phan TD, Eastwood JP, Shay MA, Drake JF, Sonnerup BUÖ, Fujimoto M, Cassak PA, Øieroset M, Burch JL, Torbert RB, Rager AC, Dorelli JC, Gershman DJ, Pollock C, Pyakurel PS, Haggerty CC, Khotyaintsev Y, Lavraud B, Saito Y, Oka M, Ergun RE, Retino A, Le Contel O, Argall MR, Giles BL, Moore TE, Wilder FD, Strangeway RJ, Russell CT, Lindqvist PA, Magnes Wet al., 2019,

    Publisher Correction: Electron magnetic reconnection without ion coupling in Earth's turbulent magnetosheath

    , Nature, Vol: 569, Pages: E9-E9, ISSN: 0028-0836

    Change history: In this Letter, the y-axis values in Fig. 3f should go from 4 to -8 (rather than from 4 to -4), the y-axis values in Fig. 3h should appear next to the major tick marks (rather than the minor ticks), and in Fig. 1b, the arrows at the top and bottom of the electron-scale current sheet were going in the wrong direction; these errors have been corrected online.
  • Journal article
    Bowen TA, Zhivun E, Wickenbrock A, Dumont V, Bale SD, Pankow C, Dobler G, Wurtele JS, Budker Det al., 2019,

    A network of magnetometers for multi-scale urban science and informatics

    , GEOSCIENTIFIC INSTRUMENTATION METHODS AND DATA SYSTEMS, Vol: 8, Pages: 129-138, ISSN: 2193-0856
  • Journal article
    Barnes D, Davies JA, Harrison RA, Byrne JP, Perry CH, Bothmer V, Eastwood JP, Gallagher PT, Kilpua EKJ, Moestl C, Rodriguez L, Rouillard AP, Odstrcil Det al., 2019,

    CMEs in the heliosphere: II. A statistical analysis of the kinematic properties derived from single-spacecraft geometrical modelling techniques applied to CMEs detected in the heliosphere from 2007 to 2017 by STEREO/HI-1

    , Solar Physics, Vol: 294, ISSN: 0038-0938

    Recent observations with the Heliospheric Imagers (HIs) onboard the twin NASA Solar Terrestrial Relations Observatory (STEREO) spacecraft have provided unprecedented observations of a large number of coronal mass ejections (CMEs) in the inner heliosphere. In this article we discuss the generation of the HIGeoCAT CME catalogue and perform a statistical analysis of its events. The catalogue was generated as part of the EU FP7 HELCATS (Heliospheric Cataloguing, Analysis and Techniques Service) project ( www.helcats-fp7.eu/ ). It is created by generating time/elongation maps for CMEs using observations from the inner (HI-1) and outer (HI-2) cameras along a position angle close to the CME apex. Next, we apply single-spacecraft geometric-fitting techniques to determine the kinematic properties of these CMEs, including their speeds, propagation directions, and launch times. The catalogue contains a total of 1455 events (801 from STEREO-A and 654 from STEREO-B) from April 2007 to the end of August 2017. We perform a statistical analysis of the properties of CMEs in HIGeoCAT and compare the results with those from the Large Angle Spectrometric Coronagraph (LASCO) CDAW catalogues (Yashiro et al.J. Geophys. Res. Space Phys.109, A07105, 2004) and the COR-2 catalogue of Vourlidas et al. (Astrophys. J.838, 141, 2004) during the same period. We find that the distributions of both speeds and latitudes for the HIGeoCAT CMEs correlate with the sunspot number over the solar cycle. We also find that the HI-derived CME speed distributions are generally consistent with coronagraph catalogues over the solar cycle, albeit with greater absolute speeds due to the differing methods with which each is derived.
  • Journal article
    Tang T, Shindell D, Faluvegi G, Myhre G, Olivié D, Voulgarakis A, Kasoar M, Andrews T, Boucher O, Forster PM, Hodnebrog, Iversen T, Kirkevåg A, Lamarque JF, Richardson T, Samset BH, Stjern CW, Takemura T, Smith Cet al., 2019,

    Comparison of effective radiative forcing calculations using multiple methods, drivers, and models

    , Journal of Geophysical Research: Atmospheres, Vol: 124, Pages: 4382-4394, ISSN: 2169-897X

    American Geophysical Union. All Rights Reserved. We compare six methods of estimating effective radiative forcing (ERF) using a set of atmosphere-ocean general circulation models. This is the first multiforcing agent, multimodel evaluation of ERF values calculated using different methods. We demonstrate that previously reported apparent consistency between the ERF values derived from fixed sea surface temperature simulations and linear regression holds for most climate forcings, excluding black carbon (BC). When land adjustment is accounted for, however, the fixed sea surface temperature ERF values are generally 10–30% larger than ERFs derived using linear regression across all forcing agents, with a much larger (~70–100%) discrepancy for BC. Except for BC, this difference can be largely reduced by either using radiative kernel techniques or by exponential regression. Responses of clouds and their effects on shortwave radiation show the strongest variability in all experiments, limiting the application of regression-based ERF in small forcing simulations.
  • Journal article
    Yang L, Wang L, Li G, Wimmer-Schweingruber RF, He J, Tu C, Tian H, Bale SDet al., 2019,

    Electron Acceleration by ICME-driven Shocks at 1 au

    , ASTROPHYSICAL JOURNAL, Vol: 875, ISSN: 0004-637X
  • Journal article
    Gryspeerdt E, Goren T, Sourdeval O, Quaas J, Mülmenstädt J, Dipu S, Unglaub C, Gettelman A, Christensen Met al., 2019,

    Constraining the aerosol influence on cloud liquid water path

    , Atmospheric Chemistry and Physics, Vol: 19, Pages: 5331-5347, ISSN: 1680-7316

    The impact of aerosols on cloud properties is one of the largest uncertainties in the anthropogenic radiative forcing of the climate. Significant progress has been made in constraining this forcing using observations, but uncertainty remains, particularly in the magnitude of cloud rapid adjustments to aerosol perturbations. Cloud liquid water path (LWP) is the leading control on liquid-cloud albedo, making it important to observationally constrain the aerosol impact on LWP.Previous modelling and observational studies have shown that multiple processes play a role in determining the LWP response to aerosol perturbations, but that the aerosol effect can be difficult to isolate. Following previous studies using mediating variables, this work investigates use of the relationship between cloud droplet number concentration (Nd) and LWP for constraining the role of aerosols. Using joint-probability histograms to account for the non-linear relationship, this work finds a relationship that is broadly consistent with previous studies. There is significant geographical variation in the relationship, partly due to role of meteorological factors (particularly relative humidity). The Nd–LWP relationship is negative in the majority of regions, suggesting that aerosol-induced LWP reductions could offset a significant fraction of the instantaneous radiative forcing from aerosol–cloud interactions (RFaci).However, variations in the Nd–LWP relationship in response to volcanic and shipping aerosol perturbations indicate that the Nd–LWP relationship overestimates the causal Nd impact on LWP due to the role of confounding factors. The weaker LWP reduction implied by these “natural experiments” means that this work provides an upper bound to the radiative forcing from aerosol-induced changes in the LWP.
  • Journal article
    Misios S, Gray LJ, Knudsen MF, Karoff C, Schmidt H, Haigh JDet al., 2019,

    Slowdown of the Walker circulation at solar cycle maximum

    , Proceedings of the National Academy of Sciences of USA, Vol: 116, Pages: 7186-7191, ISSN: 0027-8424

    The Pacific Walker Circulation (PWC) fluctuates on interannual and multidecadal timescales under the influence of internal variability and external forcings. Here, we provide observational evidence that the 11-y solar cycle (SC) affects the PWC on decadal timescales. We observe a robust reduction of east-west sea-level pressure gradients over the Indo-Pacific Ocean during solar maxima and the following 1-2 y. This reduction is associated with westerly wind anomalies at the surface and throughout the equatorial troposphere in the western/central Pacific paired with an eastward shift of convective precipitation that brings more rainfall to the central Pacific. We show that this is initiated by a thermodynamical response of the global hydrological cycle to surface warming, further amplified by atmosphere-ocean coupling, leading to larger positive ocean temperature anomalies in the equatorial Pacific than expected from simple radiative forcing considerations. The observed solar modulation of the PWC is supported by a set of coupled ocean-atmosphere climate model simulations forced only by SC irradiance variations. We highlight the importance of a muted hydrology mechanism that acts to weaken the PWC. Demonstration of this mechanism acting on the 11-y SC timescale adds confidence in model predictions that the same mechanism also weakens the PWC under increasing greenhouse gas forcing.
  • Journal article
    Hesse M, Norgren C, Tenfjord P, Burch JL, Liu YH, Chen LJ, Bessho N, Wang S, Nakamura R, Eastwood JP, Hoshino M, Torbert RB, Ergun REet al., 2019,

    Erratum: "On the role of separatrix instabilities in heating the reconnection outflow region" [Phys. Plasmas 25, 122902 (2018)]

    , Physics of Plasmas, Vol: 26, ISSN: 1070-664X

    In a recent paper1 about electron heating at the reconnection separatrix, two figures depicting the contributions to the electron energy balance and the contribution to the total, quasi-viscous heating are incorrectly displayed. The correct figures are as follows: [Table Presented].
  • Journal article
    Kajdic P, Preisser L, Blanco-Cano X, Burgess D, Trotta Det al., 2019,

    First Observations of Irregular Surface of Interplanetary Shocks at Ion Scales by <i>Cluster</i>

    , ASTROPHYSICAL JOURNAL LETTERS, Vol: 874, ISSN: 2041-8205
  • Journal article
    Lai T-K, Menelaou K, Yau MK, 2019,

    Barotropic Instability across the Moat and Inner Eyewall Dissipation: A Numerical Study of Hurricane Wilma (2005)

    , JOURNAL OF THE ATMOSPHERIC SCIENCES, Vol: 76, Pages: 989-1013, ISSN: 0022-4928
  • Book chapter
    Gryspeerdt E, 2019,

    Ruskin and Meteorology

    , Ruskin, Turner and the Storm Cloud, Editors: Cooper, Johns, Publisher: Paul Holberton Publishing, ISBN: 978-1-911300-60-1
  • Journal article
    Müller-Wodarg ICF, Koskinen TT, Moore L, Serigano J, Yelle R, Hörst S, Waite JH, Mendillo Met al., 2019,

    Atmospheric waves and their possible effect on the thermal structure of Saturn's thermosphere

    , Geophysical Research Letters, Vol: 46, Pages: 2372-2380, ISSN: 0094-8276

    Atmospheric waves have been discovered for the first time in Saturn's neutral upper atmosphere (thermosphere). Waves may be generated from instabilities, convective storms or other atmospheric phenomena. The inferred wave amplitudes change little with height within the sampled region, raising the possibility of the waves being damped, which in turn may enhance the eddy friction within the thermosphere. Using our Saturn Thermosphere Ionosphere General Circulation Model, we explore the parameter space of how an enhanced Rayleigh drag in different latitude regimes would affect the global circulation pattern within the thermosphere and, in turn, its global thermal structure. We find that Rayleigh drag of sufficient magnitude at midlatitudes may reduce the otherwise dominant Coriolis forces and enhance equatorward winds to transport energy from poles toward the equator, raising the temperatures there to observed values. Without this Rayleigh drag, energy supplied into the polar upper atmosphere by magnetosphere‐atmosphere coupling processes remains trapped at high latitudes and causes low‐latitude thermosphere temperatures to remain well below the observed levels. Our simulations thus suggest that giant planet upper atmosphere global circulation models need to include additional Rayleigh drag in order to capture the effects of physical processes otherwise not resolved by the codes.
  • Journal article
    Hanson ELM, Agapitov OV, Mozer FS, Krasnoselskikh V, Bale SD, Avanov L, Khotyaintsev Y, Giles Bet al., 2019,

    Cross-Shock Potential in Rippled Versus Planar Quasi-Perpendicular Shocks Observed by MMS

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 46, Pages: 2381-2389, ISSN: 0094-8276
  • Journal article
    Fox S, Mendrok J, Eriksson P, Ekelund R, O'Shea SJ, Bower KN, Baran AJ, Harlow RC, Pickering JCet al., 2019,

    Airborne validation of radiative transfer modelling of ice clouds at millimetre and sub-millimetre wavelengths

    , ATMOSPHERIC MEASUREMENT TECHNIQUES, Vol: 12, Pages: 1599-1617, ISSN: 1867-1381
  • Journal article
    Brophy K, Graven H, Manning AJ, White E, Arnold T, Fischer ML, Jeong S, Cui X, Rigby Met al., 2019,

    Characterizing uncertainties in atmospheric inversions of fossil fuel CO2 emissions in California

    , Atmospheric Chemistry and Physics, Vol: 19, Pages: 2991-3006, ISSN: 1680-7316

    Atmospheric inverse modelling has become an increasingly useful tool for evaluating emissions of greenhouse gases including methane, nitrous oxide, and synthetic gases such as hydrofluorocarbons (HFCs). Atmospheric inversions for emissions of CO2 from fossil fuel combustion (ffCO2) are currently being developed. The aim of this paper is to investigate potential errors and uncertainties related to the spatial and temporal prior representation of emissions and modelled atmospheric transport for the inversion of ffCO2 emissions in the US state of California. We perform simulation experiments based on a network of ground-based observations of CO2 concentration and radiocarbon in CO2 (a tracer of ffCO2), combining prior (bottom-up) emission models and transport models currently used in many atmospheric studies. The potential effect of errors in the spatial and temporal distribution of prior emission estimates is investigated in experiments by using perturbed versions of the emission estimates used to create the pseudo-data. The potential effect of transport error was investigated by using three different atmospheric transport models for the prior and pseudo-data simulations. We find that the magnitude of biases in posterior total state emissions arising from errors in the spatial and temporal distribution in prior emissions in these experiments are 1 %–15 % of posterior total state emissions and are generally smaller than the 2σ uncertainty in posterior emissions. Transport error in these experiments introduces biases of −10 % to +6 % into posterior total state emissions. Our results indicate that uncertainties in posterior total state ffCO2 estimates arising from the choice of prior emissions or atmospheric transport model are on the order of 15 % or less for the ground-based network in California we consider. We highlight the need for temporal variations to be included in prior emissions and for continuing efforts to
  • Journal article
    Stansby D, Horbury TS, Wallace S, Nick Arge Cet al., 2019,

    Predicting Large-scale Coronal Structure for Parker Solar Probe Using Open Source Software

    , Research Notes of the AAS, Vol: 3, Pages: 57-57
  • Journal article
    Perrone D, Stansby D, Horbury T, Matteini Let al., 2019,

    Radial evolution of the solar wind in pure high-speed streams: HELIOS revised observations

    , Monthly Notices of the Royal Astronomical Society, Vol: 483, Pages: 3730-3737, ISSN: 0035-8711

    Spacecraft observations have shown that the proton temperature in the solar wind falls off with radial distance more slowly than expected for an adiabatic prediction. Usually, previous studies have been focused on the evolution of the solar-wind plasma by using the bulk speed as an order parameter to discriminate different regimes. In contrast, here, we study the radial evolution of pure and homogeneous fast streams (i.e. well-defined streams of coronal-hole plasma that maintain their identity during several solar rotations) by means of re-processed particle data, from the HELIOS satellites between 0.3 and 1 au. We have identified 16 intervals of unperturbed high-speed coronal-hole plasma, from three different sources and measured at different radial distances. The observations show that, for all three streams, (i) the proton density decreases as expected for a radially expanding plasma, unlike previous analysis that found a slower decrease; (ii) the magnetic field deviates from the Parker prediction, with the radial component decreasing more slowly and the tangential more quickly than expected; (iii) the double-adiabatic invariants are violated and an increase of entropy is observed; (iv) the collisional frequency is not constant, but decreases as the plasma travels away from the Sun. This work provides an insight into the heating problem in pure fast solar wind, fitting in the context of the next solar missions, and, especially for Parker Solar Probe, it enables us to predict the high-speed solar-wind environment much closer to the Sun.
  • Journal article
    DAmicis R, Matteini L, Bruno R, 2019,

    On slow solar wind with high Alfvénicity: from composition and microphysics to spectral properties

    , Monthly Notices of the Royal Astronomical Society, Vol: 483, Pages: 4665-4677, ISSN: 0035-8711

    Alfvénic fluctuations are very common features in the solar wind and are found especially within the main portion of fast-wind streams while the slow wind usually is less Alfvénic and more variable. In general, the fast and slow winds show many differences, which span from the large-scale structure to small-scale phenomena, including also a different turbulent behaviour. Recent studies, however, have shown that even the slow wind can sometimes be highly Alfvénic, with fluctuations as large as those of the fast wind. This study is devoted to presenting many facets of this Alfvénic slow solar wind, including for example the study of the source regions and their connection to coronal structures, large-scale properties, and microscale phenomena and also impact on the spectral features. This study will be conducted performing a comparative analysis with the typical slow wind and with the fast wind. It has been found that the fast wind and the Alfvénic slow wind share common characteristics, probably attributable to their similar solar origin, that is coronal-hole solar wind. Given these similarities, it is suggested that in the Alfvénic slow wind a major role is played by the superradial expansion responsible for the lower velocity. Relevant implications of these new findings for the upcoming Solar Orbiter and Solar Probe Plus missions, and more in general for turbulence measurements close to the Sun, will be discussed.
  • Journal article
    Stansby D, Perrone D, Matteini L, Horbury T, Salem Cet al., 2019,

    Alpha particle thermodynamics in the inner heliosphere fast solar wind

    , Astronomy and Astrophysics, Vol: 623, ISSN: 0004-6361

    Context. Plasma processes occurring in the corona and solar wind can be probed by studying the thermodynamic properties ofdifferent ion species. However, most in-situ observations of positive ions in the solar wind are taken at 1 AU, where information ontheir solar source properties may have been irreversibly erased.Aims. In this study we aimed to use the properties of alpha particles at heliocentric distances between 0.3 and 1 AU to study plasmaprocesses occurring at the points of observation, and to infer processes occurring inside 0.3 AU by comparing our results to previousremote sensing observations of the plasma closer to the Sun.Methods. We reprocessed the original Helios positive ion distribution functions, isolated the alpha particle population, and computedthe alpha particle number density, velocity, and magnetic field perpendicular and parallel temperatures. We then investigated the radialvariation of alpha particle temperatures in fast solar wind observed between 0.3 and 1 AU.Results. Between 0.3 and 1 AU alpha particles are heated in the magnetic field perpendicular direction, and cooled in the magneticfield parallel direction. Alpha particle evolution is bounded by the alpha firehose instability threshold, which provides one possiblemechanism to explain the observed parallel cooling and perpendicular heating. Closer to the Sun our observations suggest that thealpha particles undergo heating in the perpendicular direction, whilst the large magnetic field parallel temperatures observed at 0.3 AUmay be due to the combined effect of double adiabatic expansion and alpha particle deceleration inside 0.3 AU.
  • Journal article
    Goodrich KA, Ergun R, Schwartz SJ, Wilson LB, Johlander A, Newman D, Wilder FD, Holmes J, Burch J, Torbert R, Khotyaintsev Y, Lindqvist P-A, Strangeway R, Gershman D, Giles Bet al., 2019,

    Impulsively Reflected Ions: A Plausible Mechanism for Ion Acoustic Wave Growth in Collisionless Shocks

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 1855-1865, ISSN: 2169-9380
  • Journal article
    Kilpua EKJ, Turner DL, Jaynes AN, Hietala H, Koskinen HEJ, Osmane A, Palmroth M, Pulkkinen T, Vainio R, Baker D, Claudepierre SGet al., 2019,

    Outer Van Allen Radiation Belt Response to Interacting Interplanetary Coronal Mass Ejectionsy

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 1927-1947, ISSN: 2169-9380
  • Journal article
    Graven H, Hocking T, Zazzeri G, 2019,

    Detection of fossil and biogenic methane at regional scales using atmospheric radiocarbon

    , Earth's Future, Vol: 7, Pages: 283-299, ISSN: 2328-4277

    Regional emissions of methane and their attribution to a variety of sources presently have large uncertainties. Measurements of radiocarbon (14C) in methane (CH4) may provide a method for identifying regional CH4 emissions from fossil versus biogenic sources because adding 14C‐free fossil carbon reduces the 14C/C ratio (Δ14CH4) in atmospheric CH4 much more than biogenic carbon does. We describe an approach for estimating fossil and biogenic CH4 at regional scales using atmospheric Δ14CH4 observations. As a case study to demonstrate expected Δ14CH4 and Δ14CH4‐CH4 relationships, we simulate and compare Δ14CH4 at a network of sites in California using two gridded CH4 emissions estimates (Emissions Database for Global Atmospheric Research, EDGAR, and Gridded Environmental Protection Agency, GEPA) and the CarbonTracker‐Lagrange model for 2014, and for 2030 under business‐as‐usual and mitigation scenarios. The fossil fraction of CH4 (F) is closely linked with the simulated Δ14CH4‐CH4 slope and differences of 2–21% in median F are found for EDGAR versus GEPA in 2014, and 7–10% for business‐as‐usual and mitigation scenarios in 2030. Differences of 10% in F for >200 ppb of added CH4 produce differences of >10‰ in Δ14CH4, which are likely detectable from regular observations. Nuclear power plant 14CH4 emissions generally have small simulated median influences on Δ14CH4 (0–7‰), but under certain atmospheric conditions they can be much stronger (>30‰) suggesting they must be considered in applications of Δ14CH4 in California. This study suggests that atmospheric Δ14CH4 measurements could provide powerful constraints on regional CH4 emissions, complementary to other monitoring techniques.
  • Journal article
    Øieroset M, Phan TD, Drake JF, Eastwood JP, Fuselier SA, Strangeway RJ, Haggerty C, Shay MA, Oka M, Wang S, Chen L-J, Kacem I, Lavraud B, Angelopoulos V, Burch JL, Torbert RB, Ergun RE, Khotyaintsev Y, Lindqvist PA, Gershman DJ, Giles BL, Pollock C, Moore TE, Russell CT, Saito Y, Avanov LA, Paterson Wet al., 2019,

    Reconnection with magnetic flux pileup at the interface of converging jets at the magnetopause

    , Geophysical Research Letters, Vol: 46, Pages: 1937-1946, ISSN: 0094-8276

    We report Magnetospheric Multiscale observations of reconnection in a thin current sheet at the interface of interlinked flux tubes carried by converging reconnection jets at Earth's magnetopause. The ion skin depth‐scale width of the interface current sheet and the non‐frozen‐in ions indicate that Magnetospheric Multiscale crossed the reconnection layer near the X‐line, through the ion diffusion region. Significant pileup of the reconnecting component of the magnetic field in this and three other events on approach to the interface current sheet was accompanied by an increase in magnetic shear and decrease in Δβ, leading to conditions favorable for reconnection at the interface current sheet. The pileup also led to enhanced available magnetic energy per particle and strong electron heating. The observations shed light on the evolution and energy release in 3‐D systems with multiple reconnection sites.
  • Journal article
    Dimmock AP, Russell CT, Sagdeev RZ, Krasnoselskikh V, Walker SN, Carr C, Dandouras I, Escoubet CP, Ganushkina N, Gedalin M, Khotyaintsev YV, Aryan H, Pulkkinen TI, Balikhin MAet al., 2019,

    Direct evidence of nonstationary collisionless shocks in space plasmas

    , Science Advances, Vol: 5, ISSN: 2375-2548

    Collisionless shocks are ubiquitous throughout the universe: around stars, supernova remnants, active galactic nuclei, binary systems, comets, and planets. Key information is carried by electromagnetic emissions from particles accelerated by high Mach number collisionless shocks. These shocks are intrinsically nonstationary, and the characteristic physical scales responsible for particle acceleration remain unknown. Quantifying these scales is crucial, as it affects the fundamental process of redistributing upstream plasma kinetic energy into other degrees of freedom-particularly electron thermalization. Direct in situ measurements of nonstationary shock dynamics have not been reported. Thus, the model that best describes this process has remained unknown. Here, we present direct evidence demonstrating that the transition to nonstationarity is associated with electron-scale field structures inside the shock ramp.
  • Journal article
    Dubois D, Carrasco N, Bourgalais J, Vettier L, Desai RT, Wellbrock A, Coates AJet al., 2019,

    Nitrogen-containing Anions and Tholin Growth in Titan's Ionosphere: Implications for Cassini CAPS-ELS Observations

    , ASTROPHYSICAL JOURNAL LETTERS, Vol: 872, ISSN: 2041-8205
  • Journal article
    Provan G, Cowley SWH, Bunce EJ, Bradley TJ, Hunt GJ, Cao H, Dougherty MKet al., 2019,

    Variability of Intra-D Ring Azimuthal Magnetic Field Profiles Observed on Cassini's Proximal Periapsis Passes

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 379-404, ISSN: 2169-9380
  • Journal article
    Gingell I, Schwartz SJ, Eastwood JP, Burch JL, Ergun RE, Fuselier S, Gershman DJ, Giles BL, Khotyaintsev Y, Lavraud B, Lindqvist P-A, Paterson WR, Phan TD, Russell CT, Stawarz JE, Strangeway RJ, Torbert RB, Wilder Fet al., 2019,

    Observations of magnetic reconnection in the ransition region of quasi-parallel hocks

    , Geophysical Research Letters, Vol: 46, Pages: 1177-1184, ISSN: 0094-8276

    Using observations of Earth's bow shock by the Magnetospheric Multiscale mission, we show for the first time that active magnetic reconnection is occurring at current sheets embedded within the quasi‐parallel shock's transition layer. We observe an electron jet and heating but no ion response, suggesting we have observed an electron‐only mode. The lack of ion response is consistent with simulations showing reconnection onset on sub‐ion time scales. We also discuss the impact of electron heating in shocks via reconnection.
  • Journal article
    Ball WT, Rozanov EV, Alsing J, Marsh DR, Tummon F, Mortlock DJ, Kinnison D, Haigh JDet al., 2019,

    The upper stratospheric solar cycle ozone response

    , Geophysical Research Letters, Vol: 46, Pages: 1831-1841, ISSN: 0094-8276

    The solar cycle (SC) stratospheric ozone response is thought to influence surface weather and climate. To understand the chain of processes and ensure climate models adequately represent them, it is important to detect and quantify an accurate SC ozone response from observations. Chemistry climate models (CCMs) and observations display a range of upper stratosphere (1–10 hPa) zonally averaged spatial responses; this and the recommended data set for comparison remains disputed. Recent data-merging advancements have led to more robust observational data. Using these data, we show that the observed SC signal exhibits an upper stratosphere U-shaped spatial structure with lobes emanating from the tropics (5–10 hPa) to high altitudes at midlatitudes (1–3 hPa). We confirm this using two independent chemistry climate models in specified dynamics mode and an idealized timeslice experiment. We recommend the BASIC v2 ozone composite to best represent historical upper stratospheric solar variability, and that those based on SBUV alone should not be used.
  • Journal article
    Archer MO, Hietala H, Hartinger MD, Plaschke F, Angelopoulos Vet al., 2019,

    Direct observations of a surface eigenmode of the dayside magnetopause

    , Nature Communications, Vol: 10, ISSN: 2041-1723

    The abrupt boundary between a magnetosphere and the surrounding plasma, the magnetopause, has long been known to support surface waves. It was proposed that impulses acting on the boundary might lead to a trapping of these waves on the dayside by the ionosphere, resulting in a standing wave or eigenmode of the magnetopause surface. No direct observational evidence of this has been found to date and searches for indirect evidence have proved inconclusive, leading to speculation that this mechanism might not occur. By using fortuitous multipoint spacecraft observations during a rare isolated fast plasma jet impinging on the boundary, here we show that the resulting magnetopause motion and magnetospheric ultra-low frequency waves at well-defined frequencies are in agreement with and can only be explained by the magnetopause surface eigenmode. We therefore show through direct observations that this mechanism, which should impact upon the magnetospheric system globally, does in fact occur.

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