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  • Journal article
    Nilsson H, Wieser GS, Behar E, Gunell H, Wieser M, Galand M, Simon Wedlund C, Alho M, Goetz C, Yamauchi M, Henri P, Odelstad E, Vigren Eet al., 2017,

    Evolution of the ion environment of comet 67P during the Rosetta mission as seen by RPC-ICA

    , Monthly Notices of the Royal Astronomical Society, Vol: 469, Pages: S252-S261, ISSN: 0035-8711

    Rosetta has followed comet 67P from low activity at more than 3.6 au heliocentric distance to high activity at perihelion (1.24 au) and then out again. We provide a general overview of the evolution of the dynamic ion environment using data from the RPC-ICA ion spectrometer. We discuss where Rosetta was located within the evolving comet magnetosphere. For the initial observations, the solar wind permeated all of the coma. In 2015 mid-April, the solar wind started to disappear from the observation region, to re-appear again in 2015 December. Low-energy cometary ions were seen at first when Rosetta was about 100 km from the nucleus at 3.6 au, and soon after consistently throughout the mission except during the excursions to farther distances from the comet. The observed flux of low-energy ions was relatively constant due to Rosetta's orbit changing with comet activity. Accelerated cometary ions, moving mainly in the antisunward direction gradually became more common as comet activity increased. These accelerated cometary ions kept being observed also after the solar wind disappeared from the location of Rosetta, with somewhat higher fluxes further away from the nucleus. Around perihelion, when Rosetta was relatively deep within the comet magnetosphere, the fluxes of accelerated cometary ions decreased, as did their maximum energy. The disappearance of more energetic cometary ions at close distance during high activity is suggested to be due to a flow pattern where these ions flow around the obstacle of the denser coma or due to charge exchange losses.
  • Journal article
    Henri P, Vallières X, Hajra R, Goetz C, Richter I, Glassmeier K-H, Galand M, Rubin M, Eriksson AI, Nemeth Z, Vigren E, Beth A, Burch JL, Carr C, Nilsson H, Tsurutani B, Wattieaux Get al., 2017,

    Diamagnetic region(s): structure of the unmagnetized plasma around Comet 67P/CG

    , Monthly Notices of the Royal Astronomical Society, Vol: 469, Pages: S372-S379, ISSN: 0035-8711

    The ESA’s comet chaser Rosetta has monitored the evolution of the ionized atmosphere of comet 67P/Churyumov–Gerasimenko (67P/CG) and its interaction with the solar wind, during more than 2 yr. Around perihelion, while the cometary outgassing rate was highest, Rosetta crossed hundreds of unmagnetized regions, but did not seem to have crossed a large-scale diamagnetic cavity as anticipated. Using in situ Rosetta observations, we characterize the structure of the unmagnetized plasma found around comet 67P/CG. Plasma density measurements from RPC-MIP are analysed in the unmagnetized regions identified with RPC-MAG. The plasma observations are discussed in the context of the cometary escaping neutral atmosphere, observed by ROSINA/COPS. The plasma density in the different diamagnetic regions crossed by Rosetta ranges from ∼100 to ∼1500 cm−3. They exhibit a remarkably systematic behaviour that essentially depends on the comet activity and the cometary ionosphere expansion. An effective total ionization frequency is obtained from in situ observations during the high outgassing activity phase of comet 67P/CG. Although several diamagnetic regions have been crossed over a large range of distances to the comet nucleus (from 50 to 400 km) and to the Sun (1.25–2.4 au), in situ observations give strong evidence for a single diamagnetic region, located close to the electron exobase. Moreover, the observations are consistent with an unstable contact surface that can locally extend up to about 10 times the electron exobase.
  • Journal article
    Ceppi P, Brient F, Zelinka MD, Hartmann DLet al., 2017,

    Cloud feedback mechanisms and their representation in global climate models

    , Wiley Interdisciplinary Reviews: WIREs Climate Change, Vol: 8, ISSN: 1757-7780

    Cloud feedback—the change in top‐of‐atmosphere radiative flux resulting from the cloud response to warming—constitutes by far the largest source of uncertainty in the climate response to CO2 forcing simulated by global climate models (GCMs). We review the main mechanisms for cloud feedbacks, and discuss their representation in climate models and the sources of intermodel spread. Global‐mean cloud feedback in GCMs results from three main effects: (1) rising free‐tropospheric clouds (a positive longwave effect); (2) decreasing tropical low cloud amount (a positive shortwave [SW] effect); (3) increasing high‐latitude low cloud optical depth (a negative SW effect). These cloud responses simulated by GCMs are qualitatively supported by theory, high‐resolution modeling, and observations. Rising high clouds are consistent with the fixed anvil temperature (FAT) hypothesis, whereby enhanced upper‐tropospheric radiative cooling causes anvil cloud tops to remain at a nearly fixed temperature as the atmosphere warms. Tropical low cloud amount decreases are driven by a delicate balance between the effects of vertical turbulent fluxes, radiative cooling, large‐scale subsidence, and lower‐tropospheric stability on the boundary‐layer moisture budget. High‐latitude low cloud optical depth increases are dominated by phase changes in mixed‐phase clouds. The causes of intermodel spread in cloud feedback are discussed, focusing particularly on the role of unresolved parameterized processes such as cloud microphysics, turbulence, and convection.
  • Journal article
    Vigren E, André M, Edberg NJT, Engelhardt IAD, Eriksson AI, Galand M, Goetz C, Henri P, Heritier K, Johansson FL, Nilsson H, Odelstad E, Rubin M, Stenberg-Wieser G, Tzou C-Y, Vallières Xet al., 2017,

    Effective ion speeds at ∼200–250 km from comet 67P/Churyumov–Gerasimenko near perihelion

    , Monthly Notices of the Royal Astronomical Society, Vol: 469, Pages: S142-S148, ISSN: 0035-8711

    In 2015 August, comet 67P/Churyumov–Gerasimenko, the target comet of the ESA Rosetta mission, reached its perihelion at ∼1.24 au. Here, we estimate for a three-day period near perihelion, effective ion speeds at distances ∼200–250 km from the nucleus. We utilize two different methods combining measurements from the Rosetta Plasma Consortium (RPC)/Mutual Impedance Probe with measurements either from the RPC/Langmuir Probe or from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA)/Comet Pressure Sensor (COPS) (the latter method can only be applied to estimate the effective ion drift speed). The obtained ion speeds, typically in the range 2–8 km s−1, are markedly higher than the expected neutral outflow velocity of ∼1 km s−1. This indicates that the ions were de-coupled from the neutrals before reaching the spacecraft location and that they had undergone acceleration along electric fields, not necessarily limited to acceleration along ambipolar electric fields in the radial direction. For the limited time period studied, we see indications that at increasing distances from the nucleus, the fraction of the ions’ kinetic energy associated with radial drift motion is decreasing.
  • Journal article
    Kinrade J, Badman SV, Bunce EJ, Tao C, Provan G, Cowley SWH, Grocott A, Gray RL, Grodent D, Kimura T, Nichols JD, Arridge CS, Radioti A, Clarke JT, Crary FJ, Pryor WR, Melin H, Baines KH, Dougherty MKet al., 2017,

    An isolated, bright cusp aurora at Saturn

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 122, Pages: 6121-6138, ISSN: 2169-9380

    Saturn's dayside aurora displays a number of morphological features poleward of the main emission region. We present an unusual morphology captured by the Hubble Space Telescope on 14 June 2014 (day 165), where for 2 h, Saturn's FUV aurora faded almost entirely, with the exception of a distinct emission spot at high latitude. The spot remained fixed in local time between 10 and 15 LT and moved poleward to a minimum colatitude of ~4°. It was bright and persistent, displaying intensities of up to 49 kR over a lifetime of 2 h. Interestingly, the spot constituted the entirety of the northern auroral emission, with no emissions present at any other local time—including Saturn's characteristic dawn arc, the complete absence of which is rarely observed. Solar wind parameters from propagation models, together with a Cassini magnetopause crossing and solar wind encounter, indicate that Saturn's magnetosphere was likely to have been embedded in a rarefaction region, resulting in an expanded magnetosphere configuration during the interval. We infer that the spot was sustained by reconnection either poleward of the cusp or at low latitudes under a strong component of interplanetary magnetic field transverse to the solar wind flow. The subsequent poleward motion could then arise from either reconfiguration of successive open field lines across the polar cap or convection of newly opened field lines. We also consider the possible modulation of the feature by planetary period rotating current systems.
  • Journal article
    Heritier KL, Henri P, Vallières X, Galand M, Odelstad E, Eriksson AI, Johansson FL, Altwegg K, Behar E, Beth A, Broiles TW, Burch JL, Carr CM, Cupido E, Nilsson H, Rubin M, Vigren Eet al., 2017,

    Vertical structure of the near-surface expanding ionosphere of comet 67P probed by Rosetta

    , Monthly Notices of the Royal Astronomical Society, Vol: 469, Pages: S118-S129, ISSN: 0035-8711

    The plasma environment has been measured for the first time near the surface of a comet. This unique data set has been acquired at 67P/Churyumov–Gerasimenko during ESA/Rosetta spacecraft's final descent on 2016 September 30. The heliocentric distance was 3.8 au and the comet was weakly outgassing. Electron density was continuously measured with Rosetta Plasma Consortium (RPC)–Mutual Impedance Probe (MIP) and RPC–LAngmuir Probe (LAP) during the descent from a cometocentric distance of 20 km down to the surface. Data set from both instruments have been cross-calibrated for redundancy and accuracy. To analyse this data set, we have developed a model driven by Rosetta Orbiter Spectrometer for Ion and Neutral Analysis–COmetary Pressure Sensor total neutral density. The two ionization sources considered are solar extreme ultraviolet radiation and energetic electrons. The latter are estimated from the RPC–Ion and Electron Sensor (IES) and corrected for the spacecraft potential probed by RPC–LAP. We have compared the results of the model to the electron densities measured by RPC–MIP and RPC–LAP at the location of the spacecraft. We find good agreement between observed and modelled electron densities. The energetic electrons have access to the surface of the nucleus and contribute as the main ionization source. As predicted, the measurements exhibit a peak in the ionospheric density close to the surface. The location and magnitude of the peak are estimated analytically. The measured ionospheric densities cannot be explained with a constant outflow velocity model. The use of a neutral model with an expanding outflow is critical to explain the plasma observations.
  • Journal article
    Haigh JD, 2017,

    acp-2017-477

    , Atmospheric Chemistry and Physics, ISSN: 1680-7316
  • Journal article
    Orr JC, Najjar RG, Aumont O, Bopp L, Bullister JL, Danabasoglu G, Doney SC, Dunne JP, Dutay J-C, Graven H, Griffies SM, John JG, Joos F, Levin I, Lindsay K, Matear RJ, McKinley GA, Mouchet A, Oschlies A, Romanou A, Schlitzer R, Tagliabue A, Tanhua T, Yool Aet al., 2017,

    Biogeochemical protocols and diagnostics for the CMIP6 Ocean Model Intercomparison Project (OMIP)

    , Geoscientific Model Development, Vol: 10, Pages: 2169-2199, ISSN: 1991-959X

    The Ocean Model Intercomparison Project (OMIP) focuses on the physics and biogeochemistry of the ocean component of Earth system models participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6). OMIP aims to provide standard protocols and diagnostics for ocean models, while offering a forum to promote their common assessment and improvement. It also offers to compare solutions of the same ocean models when forced with reanalysis data (OMIP simulations) vs. when integrated within fully coupled Earth system models (CMIP6). Here we detail simulation protocols and diagnostics for OMIP's biogeochemical and inert chemical tracers. These passive-tracer simulations will be coupled to ocean circulation models, initialized with observational data or output from a model spin-up, and forced by repeating the 1948–2009 surface fluxes of heat, fresh water, and momentum. These so-called OMIP-BGC simulations include three inert chemical tracers (CFC-11, CFC-12, SF6) and biogeochemical tracers (e.g., dissolved inorganic carbon, carbon isotopes, alkalinity, nutrients, and oxygen). Modelers will use their preferred prognostic BGC model but should follow common guidelines for gas exchange and carbonate chemistry. Simulations include both natural and total carbon tracers. The required forced simulation (omip1) will be initialized with gridded observational climatologies. An optional forced simulation (omip1-spunup) will be initialized instead with BGC fields from a long model spin-up, preferably for 2000 years or more, and forced by repeating the same 62-year meteorological forcing. That optional run will also include abiotic tracers of total dissolved inorganic carbon and radiocarbon, CTabio and 14CTabio, to assess deep-ocean ventilation and distinguish the role of physics vs. biology. These simulations will be forced by observed atmospheric histories of the three inert gases and CO2 as well as carbon isotope ratios of CO2. OMIP-BGC simulation protocols
  • Journal article
    Mistry R, Eastwood JP, Phan TD, Hietala Het al., 2017,

    Statistical properties of solar wind reconnection exhausts

    , Journal of Geophysical Research: Space Physics, Vol: 122, Pages: 5895-5909, ISSN: 2169-9380

    The solar wind provides an excellent opportunity to study the exhausts that form as a result of symmetric guide field reconnection, where spacecraft rapidly cross the exhausts far downstream of the X line. We study the statistical properties of solar wind exhausts through a superposed epoch analysis of 188 events observed at 1 AU using the Wind spacecraft. These events span a range of guide fields of 0 to 10 times the reconnecting magnetic field and inflow region plasma beta of 0.1 to 6.6. This analysis reveals that the out-of-plane magnetic field is enhanced within solar wind exhausts. Furthermore, the amount by which the plasma density and ion temperature increase from inflow region to exhaust region is found to be a function of the inflow region plasma beta and reconnection guide field, which explains the lack of these enhancements in a subset of previous observations. This dependence is consistent with the scaling of ion heating with inflow region Alfven speed, which is measured to be consistent with previous observations in the solar wind and at the magnetopause.
  • Journal article
    Radioti A, Grodent D, Gerard JC, Southwood DJ, Chane E, Bonfond B, Pryor Wet al., 2017,

    Stagnation of Saturn’s auroral emission at noon

    , Journal of Geophysical Research: Space Physics, Vol: 122, Pages: 6078-6087, ISSN: 2169-9402

    Auroral emissions serve as a powerful tool to investigate themagnetospheric processes at Saturn. Solar wind and internally driven processes largely control Saturn’s auroral morphology. The main auroral emission at Saturn is suggested to be connected with the magnetosphere - solar wind interaction, through the flow shear related to rotational dynamics. Dawn auroral enhancements are associated with intense field-aligned currents generated by hot tenuous plasma carried towards the planet in fast moving flux tubes as they return from tail reconnection site to the dayside. In this work we demonstrate, based on Cassini auroral observations, that the main auroral emission at Saturn, as it rotates from midnight to dusk via noon, occasionally stagnates near noon over a couple of hours. In half of the sequences examined, the auroral emission is blocked close to noon, while in three out of four cases, the blockage of the auroral emission is accompanied with signatures of dayside reconnection. We discuss some possible interpretations of the auroral ’blockage’ near noon. According to the first one it could be related to local time variations of the flow shear close to noon. Auroral local time variations are also suggested to be initiated by radial transport process. Alternatively, the auroral blockage at noon could be associated with a plasma circulation theory, according to which tenuously populated closed flux tubes as they return from the nightside to the morning sector experience a blockage in the equatorial plane and they cannot rotate beyond noon.
  • Journal article
    Parfitt R, Czaja A, Seo H, 2017,

    A simple diagnostic for the detection of atmospheric fronts

    , Geophysical Research Letters, Vol: 44, Pages: 4351-4358, ISSN: 1944-8007

    In this article, a simple diagnostic to identify atmospheric fronts objectively from gridded data sets is presented. For this diagnostic, fronts are identified as regions where the normalized product of the isobaric relative vorticity and horizontal temperature gradient exceeds a threshold value. The purpose is to introduce a method that is both robust and particularly straightforward in calculation. A climatology of atmospheric fronts, as well as the identification of an individual frontal system, is computed using this diagnostic. These are subsequently compared to a more traditional frontal detection method and the similarities and differences discussed.
  • Journal article
    Gryspeerdt E, Quaas J, Ferrachat S, Gettelman A, Ghan S, Lohmann U, Morrison H, Neubauer D, Partridge DG, Stier P, Takemura T, Wang H, Wang M, Zhang Ket al., 2017,

    Constraining the instantaneous aerosol influence on cloud albedo

    , Proceedings of the National Academy of Sciences of the United States of America, Vol: 114, Pages: 4899-4904, ISSN: 1091-6490

    Much of the uncertainty in estimates of the anthropogenic forcing of climate change comes from uncertainties in the instantaneous effect of aerosols on cloud albedo, known as the Twomey effect or the radiative forcing from aerosol–cloud interactions (RFaci), a component of the total or effective radiative forcing. Because aerosols serving as cloud condensation nuclei can have a strong influence on the cloud droplet number concentration (Nd), previous studies have used the sensitivity of the Nd to aerosol properties as a constraint on the strength of the RFaci. However, recent studies have suggested that relationships between aerosol and cloud properties in the present-day climate may not be suitable for determining the sensitivity of the Nd to anthropogenic aerosol perturbations. Using an ensemble of global aerosol–climate models, this study demonstrates how joint histograms between Nd and aerosol properties can account for many of the issues raised by previous studies. It shows that if the anthropogenic contribution to the aerosol is known, the RFaci can be diagnosed to within 20% of its actual value. The accuracy of different aerosol proxies for diagnosing the RFaci is investigated, confirming that using the aerosol optical depth significantly underestimates the strength of the aerosol–cloud interactions in satellite data.
  • Journal article
    Owens MJ, Riley P, Horbury TS, 2017,

    Probabilistic Solar Wind and Geomagnetic Forecasting Using an Analogue Ensemble or "Similar Day" Approach

    , Solar Physics, Vol: 292, ISSN: 0038-0938

    Effective space-weather prediction and mitigation requires accurate forecastingof near-Earth solar-wind conditions. Numerical magnetohydrodynamic models of the solarwind, driven by remote solar observations, are gaining skill at forecasting the large-scalesolar-wind features that give rise to near-Earth variations over days and weeks. There remainsa need for accurate short-term (hours to days) solar-wind forecasts, however. In thisstudy we investigate the analogue ensemble (AnEn), or “similar day”, approach that wasdeveloped for atmospheric weather forecasting. The central premise of the AnEn is thatpast variations that are analogous or similar to current conditions can be used to provide agood estimate of future variations. By considering an ensemble of past analogues, the AnEnforecast is inherently probabilistic and provides a measure of the forecast uncertainty. Weshow that forecasts of solar-wind speed can be improved by considering both speed anddensity when determining past analogues, whereas forecasts of the out-of-ecliptic magneticfield [BN] are improved by also considering the in-ecliptic magnetic-field components. Ingeneral, the best forecasts are found by considering only the previous 6 – 12 hours of observations.Using these parameters, the AnEn provides a valuable probabilistic forecast forsolar-wind speed, density, and in-ecliptic magnetic field over lead times from a few hoursto around four days. For BN, which is central to space-weather disturbance, the AnEn onlyprovides a valuable forecast out to around six to seven hours. As the inherent predictabilityof this parameter is low, this is still likely a marked improvement over other forecast methods.We also investigate the use of the AnEn in forecasting geomagnetic indices Dst and Kp.The AnEn provides a valuable probabilistic forecast of both indices out to around four days.We outline a number of future improvements to AnEn forecasts of near-Earth solar-windand geomagnetic conditions.
  • Journal article
    Wilder FD, Ergun RE, Newman DL, Goodrich KA, Trattner KJ, Goldman MV, Eriksson S, Jaynes AN, Leonard T, Malaspina DM, Ahmadi N, Schwartz SJ, Burch JL, Torbert RB, Argall MR, Giles BL, Phan TD, Le Contel O, Graham DB, Khotyaintsev YV, Strangeway RJ, Russell CT, Magnes W, Plaschke F, Lindqvist P-Aet al., 2017,

    The nonlinear behavior of whistler waves at the reconnecting dayside magnetopause as observed by the Magnetospheric Multiscale mission: A case study

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 122, Pages: 5487-5501, ISSN: 2169-9380
  • Journal article
    Yan B, Martinez-Monteagudo SI, Cooperstone JL, Riedl KM, Schwartz SJ, Balasubramaniam VMet al., 2017,

    Impact of Thermal and Pressure-Based Technologies on Carotenoid Retention and Quality Attributes in Tomato Juice

    , FOOD AND BIOPROCESS TECHNOLOGY, Vol: 10, Pages: 808-818, ISSN: 1935-5130
  • Journal article
    Innocenti ME, Cazzola E, Mistry R, Eastwood JP, Goldman MV, Newman DL, Markidis S, Lapenta Get al., 2017,

    Switch-off slow shock/rotational discontinuity structures in collisionless magnetic reconnection: What to look for in satellite observations

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 44, Pages: 3447-3455, ISSN: 0094-8276

    In Innocenti et al. (2015) we have observed and characterized for the first time Petschek-like switch-off slow shock/rotational discontinuity (SO-SS/RD) compound structures in a 2-D fully kinetic simulation of collisionless magnetic reconnection. Observing these structures in the solar wind or in the magnetotail would corroborate the possibility that Petschek exhausts develop in collisionless media as a result of single X point collisionless reconnection. Here we highlight their signatures in simulations with the aim of easing their identification in observations. The most notable signatures include a four-peaked ion current profile in the out-of-plane direction, associated ion distribution functions, increased electron and ion anisotropy downstream the SS, and increased electron agyrotropy downstream the RDs.
  • Journal article
    Ergun RE, Chen L-J, Wilder FD, Ahmadi N, Eriksson S, Usanova ME, Goodrich KA, Holmes JC, Sturner AP, Malaspina DM, Newman DL, Torbert RB, Argall MR, Lindqvist P-A, Burch JL, Webster JM, Drake JF, Price L, Cassak PA, Swisdak M, Shay MA, Graham DB, Strangeway RJ, Russell CT, Giles BL, Dorelli JC, Gershman D, Avanov L, Hesse M, Lavraud B, Le Contel O, Retino A, Phan TD, Goldman MV, Stawarz JE, Schwartz SJ, Eastwood JP, Hwang K-J, Nakamura R, Wang Set al., 2017,

    Drift waves, intense parallel electric fields, and turbulence associated with asymmetric magnetic reconnection at the magnetopause

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 44, Pages: 2978-2986, ISSN: 0094-8276

    Observations of magnetic reconnection at Earth's magnetopause often display asymmetric structures that are accompanied by strong magnetic field (B) fluctuations and large-amplitude parallel electric fields (E||). The B turbulence is most intense at frequencies above the ion cyclotron frequency and below the lower hybrid frequency. The B fluctuations are consistent with a thin, oscillating current sheet that is corrugated along the electron flow direction (along the X line), which is a type of electromagnetic drift wave. Near the X line, electron flow is primarily due to a Hall electric field, which diverts ion flow in asymmetric reconnection and accompanies the instability. Importantly, the drift waves appear to drive strong parallel currents which, in turn, generate large-amplitude (~100 mV/m) E|| in the form of nonlinear waves and structures. These observations suggest that turbulence may be common in asymmetric reconnection, penetrate into the electron diffusion region, and possibly influence the magnetic reconnection process.
  • Journal article
    Hellinger P, Landi S, Matteini L, Verdini A, Franci Let al., 2017,

    Mirror Instability in the Turbulent Solar Wind

    , ASTROPHYSICAL JOURNAL, Vol: 838, ISSN: 0004-637X

    The relationship between a decaying strong turbulence and the mirror instability in a slowly expanding plasma is investigated using two-dimensional hybrid expanding box simulations. We impose an initial ambient magnetic field perpendicular to the simulation box, and we start with a spectrum of large-scale, linearly polarized, random-phase Alfvénic fluctuations that have energy equipartition between kinetic and magnetic fluctuations and a vanishing correlation between the two fields. A turbulent cascade rapidly develops, magnetic field fluctuations exhibit a Kolmogorov-like power-law spectrum at large scales and a steeper spectrum at sub-ion scales. The imposed expansion (taking a strictly transverse ambient magnetic field) leads to the generation of an important perpendicular proton temperature anisotropy that eventually drives the mirror instability. This instability generates large-amplitude, nonpropagating, compressible, pressure-balanced magnetic structures in a form of magnetic enhancements/humps that reduce the perpendicular temperature anisotropy.
  • Journal article
    Hoang M, Altwegg K, Balsiger H, Beth A, Bieler A, Calmonte U, Combi MR, De Keyser J, Fiethe B, Fougere N, Fuselier SA, Galli A, Garnier P, Gasc S, Gombosi T, Hansen KC, Jäckel A, Korth A, Lasue J, Le Roy L, Mall U, Rème H, Rubin M, Sémon T, Toublanc D, Tzou CY, Waite JH, Wurz Pet al., 2017,

    The heterogeneous coma of comet 67P/Churyumov-Gerasimenko as seen by ROSINA: H <inf>2</inf> O, CO <inf>2</inf>, and CO from September 2014 to February 2016

    , Astronomy and Astrophysics, Vol: 600, ISSN: 0004-6361

    Context. The ESA Rosetta mission has been investigating the environment of comet 67P/Churyumov-Gerasimenko (67P) since August 2014. Among the experiments on board the spacecraft, the ROSINA experiment (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) includes two mass spectrometers to analyse the composition of neutrals and ions and a COmet Pressure Sensor (COPS) to monitor the density and velocity of neutrals in the coma. Aims. We study heterogeneities in the coma during three periods starting in October 2014 (summer in the northern hemisphere) and ending in February 2016 (end of winter in the northern hemisphere). We provide a detailed description of the main volatiles dynamics (H2O, CO2, CO) and their abundance ratios. Methods. We analysed and compared the data of the Reflectron-Type Time-Of-Flight (RTOF) mass spectrometer with data from both the Double Focusing Mass Spectrometer (DFMS) and COPS during the comet escort phase. This comparison has demonstrated that the observations performed with each ROSINA sensor are indeed consistent. Furthermore, we used a Direct Simulation Monte Carlo (DSMC) model to compare modelled densitites with in situ detections. Results. Our analysis shows how the active regions of the main volatiles evolve with the seasons with a variability mostly driven by the illumination conditions; this is the case except for an unexpected dichotomy suggesting the presence of a dust layer containing water deposited in the northern hemisphere during previous perihelions hiding the presence of CO2. The influence of various parameters is investigated in detail: distance to the comet, heliocentric distance, longitude and latitude of sub-satellite point, local time, and phase angle.
  • Journal article
    Vanniere B, Czaja A, Dacre HF, 2017,

    Contribution of the cold sector of extratropical cyclones to mean state features over the Gulf Stream in winter

    , QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Vol: 143, Pages: 1990-2000, ISSN: 0035-9009
  • Journal article
    Parfitt R, Czaja A, Kwon Y-O, 2017,

    The impact of SST resolution change in the ERA-Interim reanalysis on wintertime Gulf Stream frontal air-sea interaction

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 44, Pages: 3246-3254, ISSN: 0094-8276

    This paper examines the sensitivity to a change in sea surface temperature (SST) resolution of the interaction between atmospheric and oceanic fronts in the Gulf Stream region in the ERA-Interim reanalysis data set. Two periods are considered, January 1979 to December 2001 (SST resolution 1° × 1°) and December 2010 to February 2016 (SST resolution 0.05° × 0.05°). The winter season from the latter 6 years of high-resolution SST is compared against six random periods of six wintertime seasons from the low-resolution SST period, to assess the robustness of the result against natural climate variability. In all comparisons, a significant change in frontal air-sea sensible heat flux exchange is found that is highly correlated to the change in mean SST gradient. This leads to both increases and decreases in occurrence of atmospheric fronts and mean precipitation of up to 30%. These results reemphasize the importance of high SST resolution in resolving the influence of oceanic fronts on weather and climate.
  • Journal article
    Matteini L, Alexandrova O, Chen CHK, Lacombe Cet al., 2017,

    Electric and magnetic spectra from MHD to electron scales in the magnetosheath

    , Monthly Notices of the Royal Astronomical Society, Vol: 466, Pages: 945-951, ISSN: 0035-8711

    We investigate the transition of the turbulence from large to kinetic scales using Cluster observations. Simultaneous spectra of magnetic and electric fields in the Earth's magnetosheath from magnetohydrodynamic (MHD) to electron scales are presented for the first time. While the two spectra have approximatively similar behaviour in the fluid-MHD regime, they show different trends in the kinetic range. As the magnetic field spectrum steepens at ion scales, the electric field spectrum is characterized by a shallower power law continuing down to electron scales. Such an evolution is consistent with theoretical expectations, assuming that the turbulence is dominated by highly oblique k-vectors and that between ion and electron scales the electric field is governed by the non-ideal terms in the generalized Ohm's law. This leads to an expected linear increase of the electric-to-magnetic ratio of fluctuations, consistent with observations presented here. The influence of local whistler wave activity on electron-scale spectra is also discussed.
  • Journal article
    Cerri SS, Franci L, Califano F, Landi S, Hellinger Pet al., 2017,

    Plasma turbulence at ion scales: a comparison between particle in cell and Eulerian hybrid-kinetic approaches

    , JOURNAL OF PLASMA PHYSICS, Vol: 83, ISSN: 0022-3778
  • Journal article
    Liu F, Fiencke C, Guo J, Rieth R, Cuhls C, Dong R, Pfeiffer Eet al., 2017,

    Bioscrubber treatment of exhaust air from intensive pig production: Case study in northern Germany at mild climate condition

    , Engineering in Life Sciences, Vol: 17, Pages: 458-466, ISSN: 1618-0240

    <jats:p>Treatment by field‐scale bioscrubber of exhaust air, including ammonia (NH<jats:sub>3</jats:sub>) and the greenhouse gases methane (CH<jats:sub>4</jats:sub>), nitrous oxide (N<jats:sub>2</jats:sub>O), and carbon dioxide (CO<jats:sub>2</jats:sub>), from 13 intensive pig production houses located in northern Germany were investigated in 2013 and 2015. NH<jats:sub>3</jats:sub> removal efficiencies varied between 35 and 100% with an overall average value of 79% under the NH<jats:sub>3</jats:sub> inlet fluctuations from 34 to 755 g d<jats:sup>−1</jats:sup> m<jats:sup>−3</jats:sup> in both 2013 and 2015. Results of the electron microscopic analyses demonstrated that the bacteria <jats:italic>Nitrosomonas</jats:italic> sp. and methanotrophs <jats:italic>type I</jats:italic> were the dominant NH<jats:sub>3</jats:sub> and CH<jats:sub>4</jats:sub> oxidizers, respectively. However, overall average removal efficiencies of CH<jats:sub>4</jats:sub> was approximately zero, which means CH<jats:sub>4</jats:sub> is hard to remove in bioscrubbers under normal operation. The pH of recirculation water in the bioscrubber varied from 6.1 to 8.1, and the bioscrubbers with low pH values (&lt;7.0) had high NH<jats:sub>3</jats:sub> removal efficiencies (&gt;79%). Electrical conductivity was commonly used to diagnose the bioscrubbers’ performance; in the present study, electrical conductivity presented a significant linear relationship with dissolved inorganic nitrogen, which indicates the performance stability of the 13 selected bioscrubbers.</jats:p>
  • Conference paper
    Belmonte MT, Pickering JC, Clear C, Liggings F, Thorne APet al., 2017,

    Accurate atomic data for Galactic Surveys

    , 330th Symposium of the International-Astronomical-Union (IAU), Publisher: CAMBRIDGE UNIV PRESS, Pages: 203-205, ISSN: 1743-9213
  • Journal article
    Gershman DJ, F-Vinas A, Dorelli JC, Boardsen SA, Avanov LA, Bellan PM, Schwartz SJ, Lavraud B, Coffey VN, Chandler MO, Saito Y, Paterson WR, Fuselier SA, Ergun RE, Strangeway RJ, Russell CT, Giles BL, Pollock CJ, Torbert RB, Burch JLet al., 2017,

    Wave-particle energy exchange directly observed in a kinetic Alfven-branch wave

    , NATURE COMMUNICATIONS, Vol: 8, ISSN: 2041-1723

    Alfvén waves are fundamental plasma wave modes that permeate the universe. At small kinetic scales, they provide a critical mechanism for the transfer of energy between electromagnetic fields and charged particles. These waves are important not only in planetary magnetospheres, heliospheres and astrophysical systems but also in laboratory plasma experiments and fusion reactors. Through measurement of charged particles and electromagnetic fields with NASA’s Magnetospheric Multiscale (MMS) mission, we utilize Earth’s magnetosphere as a plasma physics laboratory. Here we confirm the conservative energy exchange between the electromagnetic field fluctuations and the charged particles that comprise an undamped kinetic Alfvén wave. Electrons confined between adjacent wave peaks may have contributed to saturation of damping effects via nonlinear particle trapping. The investigation of these detailed wave dynamics has been unexplored territory in experimental plasma physics and is only recently enabled by high-resolution MMS observations.
  • Journal article
    Fischer ML, Parazoo N, Brophy K, Cui X, Jeong S, Liu J, Keeling R, Taylor TE, Gurney K, Oda T, Graven Het al., 2017,

    Simulating estimation of California fossil fuel and biosphere carbon dioxide exchanges combining in situ tower and satellite column observations

    , Journal of Geophysical Research: Atmospheres, Vol: 122, Pages: 3653-3671, ISSN: 2169-897X

    We report simulation experiments estimating the uncertainties in California regional fossil fuel and biosphere CO2 exchanges that might be obtained by using an atmospheric inverse modeling system driven by the combination of ground‐based observations of radiocarbon and total CO2, together with column‐mean CO2 observations from NASA's Orbiting Carbon Observatory (OCO‐2). The work includes an initial examination of statistical uncertainties in prior models for CO2 exchange, in radiocarbon‐based fossil fuel CO2 measurements, in OCO‐2 measurements, and in a regional atmospheric transport modeling system. Using these nominal assumptions for measurement and model uncertainties, we find that flask measurements of radiocarbon and total CO2 at 10 towers can be used to distinguish between different fossil fuel emission data products for major urban regions of California. We then show that the combination of flask and OCO‐2 observations yields posterior uncertainties in monthly‐mean fossil fuel emissions of ~5–10%, levels likely useful for policy relevant evaluation of bottom‐up fossil fuel emission estimates. Similarly, we find that inversions yield uncertainties in monthly biosphere CO2 exchange of ~6%–12%, depending on season, providing useful information on net carbon uptake in California's forests and agricultural lands. Finally, initial sensitivity analysis suggests that obtaining the above results requires control of systematic biases below approximately 0.5 ppm, placing requirements on accuracy of the atmospheric measurements, background subtraction, and atmospheric transport modeling.
  • Journal article
    Sheldon L, Czaja A, Vanniere B, Morcrette C, Sohet B, Casado M, Smith Det al., 2017,

    A warm path for Gulf Stream - troposphere interactions

    , Tellus Series A-Dynamic Meteorology and Oceanography, Vol: 69, ISSN: 1600-0870

    Warm advection by the Gulf Stream creates a characteristic ‘tongue’ of warm water leaving a strong imprint on the sea surface temperature (SST) distribution in the western North Atlantic. This study aims at quantifying the climatological impact of this feature on cyclones travelling across this region in winter using a combination of reanalysis data and numerical experiments. It is suggested that the Gulf Stream ‘warm tongue’ is conducive to enhanced upward motion in cyclones because (i) it helps maintain a high equivalent potential temperature of air parcels at low levels which favors deep ascent in the warm conveyor belt of cyclones and (ii) because the large SST gradients to the north of the warm tongue drive a thermally direct circulation reinforcing and, possibly, destabilizing, the transverse circulation embedded in cyclones. This hypothesis is confirmed by comparing simulations at 12 km resolution from the Met Office Unified Model forced with realistic SST distribution to simulations with an SST distribution from which the Gulf Stream warm tongue was artificially removed or made colder by. It is also supported by a dynamical diagnostic applied to the ERA interim data-set over the wintertime period (1979–2012). The mechanism of oceanic forcing highlighted in this study is associated with near thermal equilibration of low level air masses with SST in the warm sector of cyclones passing over the Gulf Stream warm tongue, which is in sharp contrast to what occurs in their cold sector. It is suggested that this ‘warm path’ for the climatic impact of the Gulf Stream on the North Atlantic storm-track is not currently represented in climate models because of their coarse horizontal resolution.
  • Journal article
    Banks J, Brindley HE, Stenchikov G, Schepanski Ket al., 2017,

    Satellite retrievals of dust aerosol over the Red Sea and the Persian Gulf (2005–2015)

    , Atmospheric Chemistry and Physics, Vol: 17, Pages: 3987-4003, ISSN: 1680-7316

    The inter-annual variability of the dust aerosol presence over the Red Sea and the Persian Gulf is analysed over the period 2005–2015. Particular attention is paid to the variation in loading across the Red Sea, which has previously been shown to have a strong, seasonally dependent latitudinal gradient. Over the 11 years considered, the July mean 630 nm aerosol optical depth (AOD) derived from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) varies between 0.48 and 1.45 in the southern half of the Red Sea. In the north, the equivalent variation is between 0.22 and 0.66. The temporal and spatial pattern of variability captured by SEVIRI is also seen in AOD retrievals from the MODerate Imaging Spectroradiometer (MODIS), but there is a systematic offset between the two records. Comparisons of both sets of retrievals with ship- and land-based AERONET measurements show a high degree of correlation with biases of  <  0.08. However, these comparisons typically only sample relatively low aerosol loadings. When both records are stratified by AOD retrievals from the Multi-angle Imaging SpectroRadiometer (MISR), opposing behaviour is revealed at high MISR AODs ( >  1), with offsets of +0.19 for MODIS and −0.06 for SEVIRI. Similar behaviour is also seen over the Persian Gulf. Analysis of the scattering angles at which retrievals from the SEVIRI and MODIS measurements are typically performed in these regions suggests that assumptions concerning particle sphericity may be responsible for the differences seen.
  • Journal article
    Rabin SS, Melton JR, Lasslop G, Bachelet D, Forrest M, Hantson S, Kaplan JO, Li F, Mangeon S, Ward DS, Yue C, Arora VK, Hickler T, Kloster S, Knorr W, Nieradzik L, Spessa A, Folberth GA, Sheehan T, Voulgarakis A, Kelley DI, Prentice IC, Sitch S, Harrison S, Arneth Aet al., 2017,

    The Fire Modeling Intercomparison Project (FireMIP), phase 1: experimental and analytical protocols with detailed model descriptions

    , GEOSCIENTIFIC MODEL DEVELOPMENT, Vol: 10, Pages: 1175-1197, ISSN: 1991-959X

    The important role of fire in regulating vegetation community composition and contributions to emissions of greenhouse gases and aerosols make it a critical component of dynamic global vegetation models and Earth system models. Over 2 decades of development, a wide variety of model structures and mechanisms have been designed and incorporated into global fire models, which have been linked to different vegetation models. However, there has not yet been a systematic examination of how these different strategies contribute to model performance. Here we describe the structure of the first phase of the Fire Model Intercomparison Project (FireMIP), which for the first time seeks to systematically compare a number of models. By combining a standardized set of input data and model experiments with a rigorous comparison of model outputs to each other and to observations, we will improve the understanding of what drives vegetation fire, how it can best be simulated, and what new or improved observational data could allow better constraints on model behavior. In this paper, we introduce the fire models used in the first phase of FireMIP, the simulation protocols applied, and the benchmarking system used to evaluate the models. We have also created supplementary tables that describe, in thorough mathematical detail, the structure of each model.

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