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  • Journal article
    Kasper JC, Bale SD, Belcher JW, Berthomier M, Case AW, Chandran BDG, Curtis DW, Gallagher D, Gary SP, Golub L, Halekas JS, Ho GC, Horbury TS, Hu Q, Huang J, Klein KG, Korreck KE, Larson DE, Livi R, Maruca B, Lavraud B, Louarn P, Maksimovic M, Martinovic M, McGinnis D, Pogorelov NV, Richardson JD, Skoug RM, Steinberg JT, Stevens ML, Szabo A, Velli M, Whittlesey PL, Wright KH, Zank GP, MacDowall RJ, McComas DJ, McNutt RL, Pulupa M, Raouafi NE, Schwadron NAet al., 2019,

    Alfvenic velocity spikes and rotational flows in the near-Sun solar wind

    , Nature, Vol: 576, Pages: 228-233, ISSN: 0028-0836

    The prediction of a supersonic solar wind1 was first confirmed by spacecraft near Earth2,3 and later by spacecraft at heliocentric distances as small as 62 solar radii4. These missions showed that plasma accelerates as it emerges from the corona, aided by unidentified processes that transport energy outwards from the Sun before depositing it in the wind. Alfvénic fluctuations are a promising candidate for such a process because they are seen in the corona and solar wind and contain considerable energy5,6,7. Magnetic tension forces the corona to co-rotate with the Sun, but any residual rotation far from the Sun reported until now has been much smaller than the amplitude of waves and deflections from interacting wind streams8. Here we report observations of solar-wind plasma at heliocentric distances of about 35 solar radii9,10,11, well within the distance at which stream interactions become important. We find that Alfvén waves organize into structured velocity spikes with duration of up to minutes, which are associated with propagating S-like bends in the magnetic-field lines. We detect an increasing rotational component to the flow velocity of the solar wind around the Sun, peaking at 35 to 50 kilometres per second—considerably above the amplitude of the waves. These flows exceed classical velocity predictions of a few kilometres per second, challenging models of circulation in the corona and calling into question our understanding of how stars lose angular momentum and spin down as they age12,13,14.
  • Journal article
    McComas DJ, Christian ER, Cohen CMS, Cummings AC, Davis AJ, Desai MI, Giacalone J, Hill ME, Joyce CJ, Krimigis SM, Labrador AW, Leske RA, Malandraki O, Matthaeus WH, McNutt RL, Mewaldt RA, Mitchell DG, Posner A, Rankin JS, Roelof EC, Schwadron NA, Stone EC, Szalay JR, Wiedenbeck ME, Bale SD, Kasper JC, Case AW, Korreck KE, MacDowall RJ, Pulupa M, Stevens ML, Rouillard APet al., 2019,

    Probing the energetic particle environment near the Sun

    , NATURE, Vol: 576, Pages: 223-+, ISSN: 0028-0836
  • Journal article
    Bale SD, Badman ST, Bonnell JW, Bowen TA, Burgess D, Case AW, Cattell CA, Chandran BDG, Chaston CC, Chen CHK, Drake JF, De Wit TD, Eastwood JP, Ergun RE, Farrell WM, Fong C, Goetz K, Goldstein M, Goodrich KA, Harvey PR, Horbury TS, Howes GG, Kasper JC, Kellogg PJ, Klimchuk JA, Korreck KE, Krasnoselskikh VV, Krucker S, Laker R, Larson DE, MacDowall RJ, Maksimovic M, Malaspina DM, Martinez-Oliveros J, McComas DJ, Meyer-Vernet N, Moncuquet M, Mozer FS, Phan TD, Pulupa M, Raouafi NE, Salem C, Stansby D, Stevens M, Szabo A, Velli M, Woolley T, Wygant JRet al., 2019,

    Highly structured slow solar wind emerging from an equatorial coronal hole

    , Nature, Vol: 576, Pages: 237-242, ISSN: 0028-0836

    During the solar minimum, when the Sun is at its least active, the solar wind1,2 is observed at high latitudes as a predominantly fast (more than 500 kilometres per second), highly Alfvénic rarefied stream of plasma originating from deep within coronal holes. Closer to the ecliptic plane, the solar wind is interspersed with a more variable slow wind3 of less than 500 kilometres per second. The precise origins of the slow wind streams are less certain4; theories and observations suggest that they may originate at the tips of helmet streamers5,6, from interchange reconnection near coronal hole boundaries7,8, or within coronal holes with highly diverging magnetic fields9,10. The heating mechanism required to drive the solar wind is also unresolved, although candidate mechanisms include Alfvén-wave turbulence11,12, heating by reconnection in nanoflares13, ion cyclotron wave heating14 and acceleration by thermal gradients1. At a distance of one astronomical unit, the wind is mixed and evolved, and therefore much of the diagnostic structure of these sources and processes has been lost. Here we present observations from the Parker Solar Probe15 at 36 to 54 solar radii that show evidence of slow Alfvénic solar wind emerging from a small equatorial coronal hole. The measured magnetic field exhibits patches of large, intermittent reversals that are associated with jets of plasma and enhanced Poynting flux and that are interspersed in a smoother and less turbulent flow with a near-radial magnetic field. Furthermore, plasma-wave measurements suggest the existence of electron and ion velocity-space micro-instabilities10,16 that are associated with plasma heating and thermalization processes. Our measurements suggest that there is an impulsive mechanism associated with solar-wind energization and that micro-instabilities play a part in heating, and we provide evidence that low-latitude coronal holes are a key source of the slow solar wind.
  • Journal article
    Richardson TB, Forster PM, Smith CJ, Maycock AC, Wood T, Andrews T, Boucher O, Faluvegi G, Flaeschner D, Hodnebrog O, Kasoar M, Kirkevag A, Lamarque J-F, Muelmenstaedt J, Myhre G, Olivie D, Portmann RW, Samset BH, Shawki D, Shindell D, Stier P, Takemura T, Voulgarakis A, Watson-Parris Det al., 2019,

    Efficacy of climate forcings in PDRMIP models

    , Journal of Geophysical Research: Atmospheres, Vol: 124, Pages: 12824-12844, ISSN: 2169-897X

    Quantifying the efficacy of different climate forcings is important for understanding the real‐world climate sensitivity. This study presents a systematic multimodel analysis of different climate driver efficacies using simulations from the Precipitation Driver and Response Model Intercomparison Project (PDRMIP). Efficacies calculated from instantaneous radiative forcing deviate considerably from unity across forcing agents and models. Effective radiative forcing (ERF) is a better predictor of global mean near‐surface air temperature (GSAT) change. Efficacies are closest to one when ERF is computed using fixed sea surface temperature experiments and adjusted for land surface temperature changes using radiative kernels. Multimodel mean efficacies based on ERF are close to one for global perturbations of methane, sulfate, black carbon, and insolation, but there is notable intermodel spread. We do not find robust evidence that the geographic location of sulfate aerosol affects its efficacy. GSAT is found to respond more slowly to aerosol forcing than CO2 in the early stages of simulations. Despite these differences, we find that there is no evidence for an efficacy effect on historical GSAT trend estimates based on simulations with an impulse response model, nor on the resulting estimates of climate sensitivity derived from the historical period. However, the considerable intermodel spread in the computed efficacies means that we cannot rule out an efficacy‐induced bias of ±0.4 K in equilibrium climate sensitivity to CO2 doubling when estimated using the historical GSAT trend.
  • Journal article
    Czaja A, Frankignoul C, Minobe S, Vanniere Bet al., 2019,

    Simulating the midlatitude atmospheric circulation: What might we gain from high-resolution modeling of air-sea interactions?

    , Current Climate Change Reports, Vol: 5, Pages: 390-406, ISSN: 2198-6061

    Purpose of ReviewTo provide a snapshot of the current research on the oceanic forcing of the atmospheric circulation in midlatitudes and a concise update on previous review papers.Recent FindingsAtmospheric models used for seasonal and longer timescales predictions are starting to resolve motions so far only studied in conjunction with weather forecasts. These phenomena have horizontal scales of ~ 10–100 km which coincide with energetic scales in the ocean circulation. Evidence has been presented that, as a result of this matching of scale, oceanic forcing of the atmosphere was enhanced in models with 10–100 km grid size, especially at upper tropospheric levels. The robustness of these results and their underlying mechanisms are however unclear.SummaryDespite indications that higher resolution atmospheric models respond more strongly to sea surface temperature anomalies, their responses are still generally weaker than those estimated empirically from observations. Coarse atmospheric models (grid size greater than 100 km) will miss important signals arising from future changes in ocean circulation unless new parameterizations are developed.
  • Journal article
    Wellbrock A, Coates AJ, Jones GH, Vuitton V, Lavvas P, Desai RT, Waite JHet al., 2019,

    Heavy negative ion growth in Titan's polar winter

    , MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 490, Pages: 2254-2261, ISSN: 0035-8711
  • Conference paper
    Nowack P, Ong QYE, Braesicke P, Haigh J, Abraham L, Pyle J, Voulgarakis Aet al., 2019,

    Machine learning parameterizations for ozone: climate model transferability

    , https://sites.google.com/view/climateinformatics2019/proceedings, 9th International Workshop on Climate Informatics, Publisher: UCAR, Pages: 263-268

    Many climate modeling studies have demon-strated the importance of two-way interactions betweenozone and atmospheric dynamics. However, atmosphericchemistry models needed for calculating changes in ozoneare computationally expensive. Nowack et al. [1] high-lighted the potential of machine learning-based ozoneparameterizations in constant climate forcing simulations,with ozone being predicted as a function of the atmo-spheric temperature state. Here we investigate the roleof additional time-lagged temperature information underpreindustrial forcing conditions. In particular, we testif the use of Long Short-Term Memory (LSTM) neuralnetworks can significantly improve the predictive skill ofthe parameterization. We then introduce a novel workflowto transfer the regression model to the new UK EarthSystem Model (UKESM). For this, we show for the firsttime how machine learning parameterizations could betransferred between climate models, a pivotal step tomaking any such parameterization widely applicable inclimate science. Our results imply that ozone parame-terizations could have much-extended scope as they arenot bound to individual climate models but, once trained,could be used in a number of different models. We hope tostimulate similar transferability tests regarding machinelearning parameterizations developed for other Earthsystem model components such as ocean eddy modeling,convection, clouds, or carbon cycle schemes.
  • Conference paper
    Weiss Z, Pickering JC, Hoffmann V, 2019,

    Sixty years of spectroscopic research: a tribute to Professor Edward B. M. Steers

    , 16th Czech-Slovak Spectroscopic Conference (CSSC), Publisher: SPRINGER INTERNATIONAL PUBLISHING AG, Pages: 2891-2896, ISSN: 2585-7290
  • Journal article
    Scannell C, Booth BBB, Dunstone NJ, Rowell DP, Bernie DJ, Kasoar M, Voulgarakis A, Wilcox LJ, Acosta Navarro JC, Seland O, Paynter DJet al., 2019,

    The influence of remote aerosol forcing from industrialized economies on the future evolution of East and West African rainfall

    , Journal of Climate, Vol: 32, Pages: 8335-8354, ISSN: 0894-8755

    Past changes in global industrial aerosol emissions have played a significant role in historical shifts in African rainfall, and yet assessment of the impact on African rainfall of near-term (10–40 yr) potential aerosol emission pathways remains largely unexplored. While existing literature links future aerosol declines to a northward shift of Sahel rainfall, existing climate projections rely on RCP scenarios that do not explore the range of air quality drivers. Here we present projections from two emission scenarios that better envelop the range of potential aerosol emissions. More aggressive emission cuts result in northward shifts of the tropical rainbands whose signal can emerge from expected internal variability on short, 10–20-yr time horizons. We also show for the first time that this northward shift also impacts East Africa, with evidence of delays to both onset and withdrawal of the short rains. However, comparisons of rainfall impacts across models suggest that only certain aspects of both the West and East African model responses may be robust, given model uncertainties. This work motivates the need for wider exploration of air quality scenarios in the climate science community to assess the robustness of these projected changes and to provide evidence to underpin climate adaptation in Africa. In particular, revised estimates of emission impacts of legislated measures every 5–10 years would have a value in providing near-term climate adaptation information for African stakeholders.
  • Journal article
    Verscharen D, Chandran BDG, Jeong S-Y, Salem CS, Pulupa MP, Bale SDet al., 2019,

    Self-induced Scattering of Strahl Electrons in the Solar Wind

    , ASTROPHYSICAL JOURNAL, Vol: 886, ISSN: 0004-637X
  • Journal article
    Ergun RE, Hoilijoki S, Ahmadi N, Schwartz SJ, Wilder FD, Burch JL, Torbert RB, Lindqvist P-A, Graham DB, Strangeway RJ, Le Contel O, Holmes JC, Stawarz JE, Goodrich KA, Eriksson S, Giles BL, Gershman D, Chen LJet al., 2019,

    Magnetic Reconnection in Three Dimensions: Observations of Electromagnetic Drift Waves in the Adjacent Current Sheet

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 10104-10118, ISSN: 2169-9380
  • Journal article
    Hoilijoki S, Ergun RE, Schwartz SJ, Eriksson S, Wilder FD, Webster JM, Ahmadi N, Le Contel O, Burch JL, Torbert RB, Strangeway RJ, Giles BLet al., 2019,

    Electron-Scale Magnetic Structure Observed Adjacent to an Electron Diffusion Region at the Dayside Magnetopause

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 10153-10169, ISSN: 2169-9380
  • Journal article
    Wilson LB, Chen L-J, Wang S, Schwartz SJ, Turner DL, Stevens ML, Kasper JC, Osmane A, Caprioli D, Bale SD, Pulupa MP, Salem CS, Goodrich KAet al., 2019,

    Electron Energy Partition across Interplanetary Shocks. II. Statistics

    , ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, Vol: 245, ISSN: 0067-0049
  • Journal article
    Ergun RE, Hoilijoki S, Ahmadi N, Schwartz SJ, Wilder FD, Drake JF, Hesse M, Shay MA, Ji H, Yamada M, Graham DB, Cassak PA, Swisdak M, Burch JL, Torbert RB, Holmes JC, Stawarz JE, Goodrich KA, Eriksson S, Strangeway RJ, LeContel Oet al., 2019,

    Magnetic Reconnection in Three Dimensions: Modeling and Analysis of Electromagnetic Drift Waves in the Adjacent Current Sheet

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 10085-10103, ISSN: 2169-9380
  • Journal article
    Sparks N, Hon KK, Chan PW, Wang S, Chan JCL, Lee TC, Toumi Ret al., 2019,

    Aircraft observations of tropical cyclone boundary layer turbulence over the South China Sea

    , Journal of the Atmospheric Sciences, Vol: 76, Pages: 3773-3783, ISSN: 0022-4928

    There have been no high-frequency aircraft observations of tropical cyclone (TC) eyewall boundary layer turbulence since two flights into Atlantic hurricanes in the 1980s. We present an analysis of the first TC boundary layer flight observations in the South China Sea by the Hong Kong Observatory comprising four eyewall penetrations. We derive the vertical flux of momentum and vertical momentum diffusivity from observed turbulence parameters. We observe negative (upward) vertical fluxes of tangential momentum near the eyewall consistent with a jet below the flight level near the radius of maximum wind. Our observations of vertical momentum diffusivity support a superlinear relationship between diffusivity and wind speed at the high wind speeds in the inner-core of TCs (power-law exponent of 1.73 ± 0.20) while the few existing boundary layer hurricane observations in the North Atlantic suggest a more linear relationship.
  • Journal article
    Turc L, Roberts OW, Archer MO, Palmroth M, Battarbee M, Brito T, Ganse U, Grandin M, Pfau-Kempf Y, Escoubet CP, Dandouras Iet al., 2019,

    First observations of the disruption of the Earth's foreshock wave field During magnetic clouds

    , Geophysical Research Letters, Vol: 46, Pages: 12644-12653, ISSN: 0094-8276

    The foreshock, extending upstream of Earth's bow shock, is a region of intense electromagnetic wave activity and nonlinear phenomena, which can have global effects on geospace. It is also the first geophysical region encountered by solar wind disturbances journeying toward Earth. Here, we present the first observations of considerable modifications of the foreshock wave field during extreme events of solar origin called magnetic clouds. Cluster's multispacecraft data reveal that the typical quasi‐monochromatic foreshock waves can be completely replaced by a superposition of waves each with shorter correlation lengths. Global numerical simulations further confirm that the foreshock wave field is more intricate and organized at smaller scales. Ion measurements suggest that changes in shock‐reflected particle properties may cause these modifications of the wave field. This state of the foreshock is encountered only during extreme events at Earth, but intense magnetic fields are typical close to the Sun or other stars.
  • Journal article
    Hasekamp OP, Gryspeerdt E, Quaas J, 2019,

    Analysis of polarimetric satellite measurements suggests stronger cooling due to aerosol-cloud interactions

    , Nature Communications, Vol: 9, ISSN: 2041-1723

    Anthropogenic aerosol emissions lead to an increase in the amount of Cloud Condensation Nuclei and consequently an increase in cloud droplet number concentration and cloud albedo. The cor-responding negative radiative forcing due to aerosol cloud interactions (RFaci) is one of the most uncertain radiative forcing terms as reported in the 5th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). We show that previous observation-based studies underestimate aerosol-cloud interactions because they used measurements of aerosol optical properties that are not directly related to cloud formation and are hampered by measurement uncertainties. We have overcome this problem by the use of new polarimetric satellite retrievals of the relevant aerosol properties (aerosol number, size, shape). The resulting estimate of RFaci= -1.14 Wm−2(range be-tween -0.84 and -1.72 Wm−2) is more than a factor 2 stronger than the IPCC estimate that includes
  • Journal article
    Schwartz SJ, Andersson L, Xu S, Mitchell DL, Akbari H, Ergun RE, Mazelle C, Thaller SA, Sales ARN, Horaites K, DiBraccio GA, Meziane Ket al., 2019,

    Collisionless Electron Dynamics in the Magnetosheath of Mars

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 46, Pages: 11679-11688, ISSN: 0094-8276
  • Journal article
    Lin Y, Hwang Y, Ceppi P, Gregory Jet al., 2019,

    Uncertainty in the evolution of climate feedback traced to the strength of the Atlantic Meridional Overturning Circulation

    , Geophysical Research Letters, Vol: 46, Pages: 12331-12339, ISSN: 0094-8276

    In most coupled climate models, effective climate sensitivity increases for a few decades following an abrupt CO2 increase. The change in the climate feedback parameter between the first 20 years and the subsequent 130 years is highly model dependent. In this study, we suggest that the intermodel spread of changes in climate feedback can be partially traced to the evolution of the Atlantic Meridional Overturning Circulation. Models with stronger Atlantic Meridional Overturning Circulation recovery tend to project more amplified warming in the Northern Hemisphere a few decades after a quadrupling of CO2. Tropospheric stability then decreases as the Northern Hemisphere gets warmer, which leads to an increase in both the lapse‐rate and shortwave cloud feedbacks. Our results suggest that constraining future ocean circulation changes will be necessary for accurate climate sensitivity projections.
  • Journal article
    Gryspeerdt E, Smith T, O'Keeffe E, Christensen M, Goldsworth Fet al., 2019,

    The impact of ship emission controls recorded by cloud properties

    , Geophysical Research Letters, Vol: 46, Pages: 12547-12555, ISSN: 0094-8276

    The impact of aerosols on cloud properties is one of the leading uncertainties in the human forcing of the climate. Ships are large, isolated sources of aerosol creating linear cloud formations known as shiptracks. These are an ideal opportunity to identify and measure aerosol-cloud interactions. This work uses over 17,000 shiptracks during the implementation of fuel sulphur content regulations to demonstrate the central role of sulphate aerosol in ship exhaust for modifying clouds. By connecting individual shiptracks to transponder data, it is shown that almost half of shiptracks are likely undetected, masking a significant contribution to the climate impact of shipping. A pathway to retrieving ship sulphate emissions is demonstrated, showing how cloud observations could be used to monitor air pollution.
  • Journal article
    Siddle AG, Mueller-Wodarg ICF, Stone SW, Yelle RVet al., 2019,

    Global characteristics of gravity waves in the upper atmosphere of Mars as measured by MAVEN/NGIMS

    , Icarus, Vol: 333, Pages: 12-21, ISSN: 0019-1035

    We present an analysis of gravity waves in Mars' upper atmosphere above 120 km. Using in-situ data from NGIMS onboard MAVEN we have been able to characterise waves from nearly 4000 orbits. We have used temperature and density profiles to extract perturbations and interpret these as vertically propagating gravity waves which we characterise by their amplitude and wavelength. In this region of the atmosphere gravity waves have amplitudes of around 10%. Vertical wavelengths are found to be around 10–30 km. We observe an increase in gravity wave amplitudes with increasing solar zenith angle. Gravity wave amplitudes appear invariant in altitude on the dayside, however increase with altitude on the nightside.
  • Journal article
    Trenchi L, Coxon JC, Fear RC, Eastwood JP, Dunlop MW, Trattner KJ, Gershman DJ, Graham DB, Khotyaintsev Y, Lavraud Bet al., 2019,

    Signatures of magnetic separatrices at the borders of a crater flux transfer event connected to an active X‐line

    , Journal of Geophysical Research: Space Physics, Vol: 124, Pages: 8600-8616, ISSN: 2169-9380

    In this paper, we present Magnetospheric Multiscale (MMS) observations of a flux transfer event (FTE) characterized by a clear signature in the magnetic field magnitude, which shows maximum at the center flanked by two depressions, detected during a period of stable southward interplanetary magnetic field. This class of FTEs are called “crater‐FTEs” and have been suggested to be connected with active reconnection X line. The MMS burst mode data allow the identification of intense fluctuations in the components of the electric field and electron velocity parallel to the magnetic field at the borders of the FTE, which are interpreted as signatures of the magnetic separatrices. In particular, the strong and persistent fluctuations of the parallel electron velocity at the borders of this crater‐FTE reported for the first time in this paper, sustain the field‐aligned current part of the Hall current system along the separatrix layer, and confirm that this FTE is connected with an active reconnection X line. Our observations suggest a stratification of particles inside the reconnection layer, where electrons are flowing toward the X line along the separatrix, are flowing away from the X line along the reconnected field lines adjacent to the separatrices, and more internally ions and electrons are flowing away from the X line with comparable velocities, forming the reconnection jets. This stratification of the reconnection layer forming the FTE, together with the reconnection jet at the trailing edge of the FTE, suggests clearly that this FTE is formed by the single X line generation mechanism.
  • Journal article
    Ceppi P, Shepherd TG, 2019,

    Contributions of climate feedbacks to changes in atmospheric circulation

    , Journal of Climate, Vol: 30, Pages: 9097-9118, ISSN: 0894-8755

    The projected response of the atmospheric circulation to the radiative changes induced by CO2 forcing and climate feedbacks is currently uncertain. In this modeling study, the impact of CO2-induced climate feedbacks on changes in jet latitude and speed is assessed by imposing surface albedo, cloud, and water vapor feedbacks as if they were forcings in two climate models, CAM4 and ECHAM6. The jet response to radiative feedbacks can be broadly interpreted through changes in midlatitude baroclinicity. Clouds enhance baroclinicity, favoring a strengthened, poleward-shifted jet; this is mitigated by surface albedo changes, which have the opposite effect on baroclinicity and the jet, while water vapor has opposing effects on upper- and lower-level baroclinicity with little net impact on the jet. Large differences between the CAM4 and ECHAM6 responses illustrate how model uncertainty in radiative feedbacks causes a large spread in the baroclinicity response to CO2 forcing. Across the CMIP5 models, differences in shortwave feedbacks by clouds and albedo are a dominant contribution to this spread. Forcing CAM4 with shortwave cloud and albedo feedbacks from a representative set of CMIP5 models yields a wide range of jet responses that strongly correlate with the meridional gradient of the anomalous shortwave heating and the associated baroclinicity response. Differences in shortwave feedbacks statistically explain about 50% of the intermodel spread in CMIP5 jet shifts for the set of models used, demonstrating the importance of constraining radiative feedbacks for accurate projections of circulation changes.
  • Journal article
    Hofstadter M, Simon A, Atreya S, Banfield D, Fortney Jonathan, Hayes A, Hedman M, Hospodarsky G, Mandt K, Masters A, Showalter M, Soderlund K, Turrini D, Turtle E, Reh K, Elliot J, Arora N, Petropoulos A, Ice giant mission study teamet al., 2019,

    Uranus and Neptune missions: a study in advance of the next Planetary Science Decadal Survey

    , Planetary and Space Science, Vol: 177, ISSN: 0032-0633

    The ice giant planets, Uranus and Neptune, represent an important and unexplored class of planets. Mostof our detailed information about themcomes from fleeting looks by the Voyager 2 spacecraftin the 1980s.Voyager,and ground-based work since then, found that these planets, their satellites, rings, and magnetospheres, challenge our understanding of the formation and evolution of planetarysystems. We also now knowthat Uranus-Neptune size planetsare common around other stars. These are some of the reasons ice giant exploration was a high priority in NASA’smost recent Planetary Science Decadal Survey. In preparation for the next Decadal Survey,NASA, with ESA participation,conducted a broad study of possible ice giant missions in the 2024 –2037 timeframe. This paper summarizes the key resultsof the study,and addressesquestionsthat have been raised by the science communityand in a recent NASA review. Foremost amongstthese are questions about the science objectives, the science payload, and the importance of an atmospheric probe. Theconclusions ofthe NASA/ESA study remain valid. In particular, it is a high priority to sendan orbiterand atmospheric probeto at least one of the ice giants, with instrumentationto studyall components of an ice giant system.Uranus and Neptune are found to be equally compelling as science targets. The two planets are not equivalent, however, and each systemhas thingsto teach us the other cannot. An additional mission study is needed to refine plans for future exploration of these worlds.
  • Journal article
    Jackman CM, Thomsen MF, Dougherty MK, 2019,

    Survey of Saturn's Magnetopause and Bow Shock Positions Over the Entire Cassini Mission: Boundary Statistical Properties and Exploration of Associated Upstream Conditions

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 8865-8883, ISSN: 2169-9380
  • Journal article
    Provan G, Cowley SWH, Bradley TJ, Bunce EJ, Hunt GJ, Cao H, Dougherty MKet al., 2019,

    Magnetic Field Observations on Cassini's Proximal Periapsis Passes: Planetary Period Oscillations and Mean Residual Fields

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 8814-8864, ISSN: 2169-9380
  • Journal article
    Hodnebrog O, Myhre G, Samset BH, Alterskjaer K, Andrews T, Boucher O, Faluvegi G, Flaeschner D, Forster PM, Kasoar M, Kirkevag A, Lamarque J-F, Olivie D, Richardson TB, Shawki D, Shindell D, Shine KP, Stier P, Takemura T, Voulgarakis A, Watson-Parris Det al., 2019,

    Water vapour adjustments and responses differ between climate drivers

    , Atmospheric Chemistry and Physics, Vol: 19, Pages: 12887-12899, ISSN: 1680-7316

    Water vapour in the atmosphere is the source of a major climate feedback mechanism and potential increases in the availability of water vapour could have important consequences for mean and extreme precipitation. Future precipitation changes further depend on how the hydrological cycle responds to different drivers of climate change, such as greenhouse gases and aerosols. Currently, neither the total anthropogenic influence on the hydrological cycle nor that from individual drivers is constrained sufficiently to make solid projections. We investigate how integrated water vapour (IWV) responds to different drivers of climate change. Results from 11 global climate models have been used, based on simulations where CO2, methane, solar irradiance, black carbon (BC), and sulfate have been perturbed separately. While the global-mean IWV is usually assumed to increase by ∼7 % per kelvin of surface temperature change, we find that the feedback response of IWV differs somewhat between drivers. Fast responses, which include the initial radiative effect and rapid adjustments to an external forcing, amplify these differences. The resulting net changes in IWV range from 6.4±0.9 % K−1 for sulfate to 9.8±2 % K−1 for BC. We further calculate the relationship between global changes in IWV and precipitation, which can be characterized by quantifying changes in atmospheric water vapour lifetime. Global climate models simulate a substantial increase in the lifetime, from 8.2±0.5 to 9.9±0.7 d between 1986–2005 and 2081–2100 under a high-emission scenario, and we discuss to what extent the water vapour lifetime provides additional information compared to analysis of IWV and precipitation separately. We conclude that water vapour lifetime changes are an important indicator of changes in precipitation patterns and that BC is particularly efficient in prolonging the mean time, and therefore like
  • Journal article
    Starkey MJ, Fuselier SA, Desai M, Burch JL, Gomez RG, Mukherjee J, Russell CT, Lai H, Schwartz SJet al., 2019,

    Acceleration of Interstellar Pickup He<SUP>+</SUP> at Earth's Perpendicular Bow Shock

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 46, Pages: 10735-10743, ISSN: 0094-8276
  • Journal article
    Nakamura T, Stawarz JE, Hasegawa H, Narita Y, Franci L, Wilder FD, Nakamura R, Nystrom WDet al., 2019,

    Effects of fluctuating magnetic field on the growth of the Kelvin-Helmholtz instability at the Earth's magnetopause
  • Journal article
    Cerri SS, Groselj D, Franci L, 2019,

    Kinetic Plasma Turbulence: Recent Insights and Open Questions From 3D3V Simulations

    , FRONTIERS IN ASTRONOMY AND SPACE SCIENCES, Vol: 6, ISSN: 2296-987X

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