Search or filter publications

Filter by type:

Filter by publication type

Filter by year:

to

Results

  • Showing results for:
  • Reset all filters

Search results

  • Journal article
    Plaschke F, Hietala H, Vörös Z, 2020,

    Scale sizes of magnetosheath jets

    , Journal of Geophysical Research: Space Physics, Vol: 125, Pages: 1-12, ISSN: 2169-9380

    Magnetosheath jets are plasma entities that feature a significantly enhanced dynamic pressure with respect to the ambient plasma. They occur more often downstream of the quasi‐parallel bow shock. Jets can propagate through the entire magnetosheath and impact on the magnetopause. We reanalyze multi‐spacecraft data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission to obtain the first unbiased distributions of scale sizes of the jets, in the directions parallel and perpendicular to their propagation direction. These distributions are log‐normal; they fit well to the observations. We argue that jet scales should be log‐normally distributed as they should result from multiplicative processes in the foreshock and in the magnetosheath. We find that typical jet scales are on the order of 0.1 Earth radii (RE), one order of magnitude smaller than previously reported. Median scale sizes of 0.12 RE and 0.15 RE in the perpendicular and parallel directions are obtained. The small scales may be related to the substructure of Short Large Amplitude Magnetic Structures (SLAMS) in the foreshock, or to the break up of larger jets within the magnetosheath. Use of the log‐normal distributions also allows for an analysis of impact rates of small‐scale jets: While previous results on large jets hitting the magnetopause several times per hour remain largely unchanged, we now find that hundreds to thousands of mostly small‐scale jets could potentially impact the dayside magnetopause every hour.
  • Journal article
    Zhu X, He J, Verscharen D, Duan D, Bale SDet al., 2020,

    Wave Composition, Propagation, and Polarization of Magnetohydrodynamic Turbulence within 0.3 au as Observed by Parker Solar Probe

    , ASTROPHYSICAL JOURNAL LETTERS, Vol: 901, ISSN: 2041-8205
  • Journal article
    Good SW, Kilpua EKJ, Ala-Lahti M, Osmane A, Bale SD, Zhao L-Let al., 2020,

    Cross Helicity of the 2018 November Magnetic Cloud Observed by the Parker Solar Probe

    , ASTROPHYSICAL JOURNAL LETTERS, Vol: 900, ISSN: 2041-8205
  • Journal article
    Shatwell P, Czaja A, Ferreira D, 2020,

    Ocean heat storage rate unaffected by MOC weakening in an idealized climate model

    , Geophysical Research Letters, Vol: 47, Pages: 1-9, ISSN: 0094-8276

    To study the role of the Atlantic meridional overturning circulation (AMOC) in transient climate change, we perform an abrupt CO2‐doubling experiment using a coupled atmosphere‐ocean‐ice model with a simple geometry that separates the ocean into small and large basins. The small basin exhibits an overturning circulation akin to the AMOC. Over the simulated 200 years of change, it stores heat at a faster rate than the large basin by 0.6 ± 0.2 W m−2. We argue that this is due to the small basin MOC. However, we find that as the MOC weakens significantly, it has little impact on the small basin's heat storage rate. We suggest this is due to the effects of both compensating warming patterns and interbasin heat transports. Thus, although the presence of a MOC is important for enhanced heat storage, MOC weakening is surprisingly unimportant.
  • Journal article
    Bantges R, 2020,

    Authors' responses to the referees' comments
  • Journal article
    Walker AP, De Kauwe MG, Bastos A, Belmecheri S, Georgiou K, Keeling R, McMahon SM, Medlyn BE, Moore DJP, Norby RJ, Zaehle S, Anderson-Teixeira KJ, Battipaglia G, Brienen RJW, Cabugao KG, Cailleret M, Campbell E, Canadell J, Ciais P, Craig ME, Ellsworth D, Farquhar G, Fatichi S, Fisher JB, Frank D, Graven H, Gu L, Haverd V, Heilman K, Heimann M, Hungate BA, Iversen CM, Joos F, Jiang M, Keenan TF, Knauer J, Körner C, Leshyk VO, Leuzinger S, Liu Y, MacBean N, Malhi Y, McVicar T, Penuelas J, Pongratz J, Powell AS, Riutta T, Sabot MEB, Schleucher J, Sitch S, Smith WK, Sulman B, Taylor B, Terrer C, Torn MS, Treseder K, Trugman AT, Trumbore SE, van Mantgem PJ, Voelker SL, Whelan ME, Zuidema PAet al., 2020,

    Integrating the evidence for a terrestrial carbon sink caused by increasing atmospheric CO2.

    , New Phytologist, ISSN: 0028-646X

    Atmospheric carbon dioxide concentration ([CO2 ]) is increasing, which increases leaf-scale photosynthesis and intrinsic water-use efficiency. These direct responses have the potential to increase plant growth, vegetation biomass, and soil organic matter; transferring carbon from the atmosphere into terrestrial ecosystems (a carbon sink). A substantial global terrestrial carbon sink would slow the rate of [CO2 ] increase and thus climate change. However, ecosystem CO2 -responses are complex or confounded by concurrent changes in multiple agents of global change and evidence for a [CO2 ]-driven terrestrial carbon sink can appear contradictory. Here we synthesise theory and broad, multi-disciplinary evidence for the effects of increasing [CO2 ] (iCO2) on the global terrestrial carbon sink. Evidence suggests a substantial increase in global photosynthesis since pre-industry. Established theory, supported by experiments, indicates that iCO2 is likely responsible for about half of the increase. Global carbon budgeting, atmospheric data, and forest inventories indicate a historical carbon sink, and these apparent iCO2-responses are high in comparison with experiments and theory. Plant mortality and soil carbon iCO2-responses are highly uncertain. In conclusion, a range of evidence supports a positive terrestrial carbon sink in response to iCO2, albeit with uncertain magnitude and strong suggestion of a role for additional agents of global change.
  • Journal article
    Madanian H, Burch JL, Eriksson AI, Cravens TE, Galand M, Vigren E, Goldstein R, Nemeth Z, Mokashi P, Richter I, Rubin Met al., 2020,

    Electron dynamics near diamagnetic regions of comet 67P/Churyumov- Gerasimenko

    , Planetary and Space Science, Vol: 187, ISSN: 0032-0633

    The Rosetta spacecraft detected transient and sporadic diamagnetic regions around comet 67P/Churyumov-Gerasimenko. In this paper we present a statistical analysis of bulk and suprathermal electron dynamics, as well as a case study of suprathermal electron pitch angle distributions (PADs) near a diamagnetic region. Bulk electron densities are correlated with the local neutral density and we find a distinct enhancement in electron densities measured over the southern latitudes of the comet. Flux of suprathermal electrons with energies between tens of eV to a couple of hundred eV decreases each time the spacecraft enters a diamagnetic region. We propose a mechanism in which this reduction can be explained by solar wind electrons that are tied to the magnetic field and after having been transported adiabatically in a decaying magnetic field environment, have limited access to the diamagnetic regions. Our analysis shows that suprathermal electron PADs evolve from an almost isotropic outside the diamagnetic cavity to a field-aligned distribution near the boundary. Electron transport becomes chaotic and non-adiabatic when electron gyroradius becomes comparable to the size of the magnetic field line curvature, which determines the upper energy limit of the flux variation. This study is based on Rosetta observations at around 200 ​km cometocentric distance when the comet was at 1.24 AU from the Sun and during the southern summer cometary season.
  • Journal article
    Franci L, Stawarz JE, Papini E, Hellinger P, Nakamura T, Burgess D, Landi S, Verdini A, Matteini L, Ergun R, Contel OL, Lindqvist P-Aet al., 2020,

    Modeling MMS observations at the Earth's magnetopause with hybrid simulations of Alfvénic turbulence

    , The Astrophysical Journal, Vol: 898, ISSN: 0004-637X

    Magnetospheric Multiscale (MMS) observations of plasma turbulence generated by a Kelvin–Helmholtz (KH) event at the Earth's magnetopause are compared with a high-resolution two-dimensional (2D) hybrid direct numerical simulation of decaying plasma turbulence driven by large-scale balanced Alfvénic fluctuations. The simulation, set up with four observation-driven physical parameters (ion and electron betas, turbulence strength, and injection scale), exhibits a quantitative agreement on the spectral, intermittency, and cascade-rate properties with in situ observations, despite the different driving mechanisms. Such agreement demonstrates a certain universality of the turbulent cascade from magnetohydrodynamic to sub-ion scales, whose properties are mainly determined by the selected parameters, also indicating that the KH instability-driven turbulence has a quasi-2D nature. The fact that our results are compatible with the validity of the Taylor hypothesis, in the whole range of scales investigated numerically, suggests that the fluctuations at sub-ion scales might have predominantly low frequencies. This would be consistent with a kinetic Alfvén wave-like nature and/or with the presence of quasi-static structures. Finally, the third-order structure function analysis indicates that the cascade rate of the turbulence generated by a KH event at the magnetopause is an order of magnitude larger than in the ambient magnetosheath.
  • Journal article
    Farrell WM, MacDowall RJ, Gruesbeck JR, Bale SD, Kasper JCet al., 2020,

    Magnetic Field Dropouts at Near-Sun Switchback Boundaries: A Superposed Epoch Analysis

    , ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, Vol: 249, ISSN: 0067-0049
  • Journal article
    Hofstadter MD, Fletcher LN, Simon AA, Masters A, Turrini D, Arridge CSet al., 2020,

    Future missions to the giant planets that can advance atmospheric science objectives

    , Space Science Reviews, Vol: 216, Pages: 1-17, ISSN: 0038-6308

    Other papers in this special issue have discussed the diversity of planetary atmospheres and some of the key science questions for giant planet atmospheres to be addressed in the future. There are crucial measurements that can only be made by orbiters of giant planets and probes dropped into their atmospheres. To help the community be more effective developers of missions and users of data products, we summarize how NASA and ESA categorize their planetary space missions, and the restrictions and requirements placed on each category. We then discuss the atmospheric goals to be addressed by currently approved giant-planet missions as well as missions likely to be considered in the next few years, such as a joint NASA/ESA Ice Giant orbiter with atmospheric probe. Our focus is on interplanetary spacecraft, but we acknowledge the crucial role to be played by ground-based and near-Earth telescopes, as well as theoretical and laboratory work.
  • Journal article
    Vasko IY, Kuzichev I, Artemyev A, Bale SD, Bonnell JW, Mozer FSet al., 2020,

    On quasi-parallel whistler waves in the solar wind

    , PHYSICS OF PLASMAS, Vol: 27, ISSN: 1070-664X
  • Journal article
    Simon Wedlund C, Behar E, Nilsson H, Alho M, Kallio E, Gunell H, Bodewits D, Heritier K, Galand M, Beth A, Rubin M, Altwegg K, Volwerk M, Gronoff G, Hoekstra Ret al., 2020,

    Solar wind charge exchange in cometary atmospheresII. Analytical model

    , Astronomy and Astrophysics: a European journal, Vol: 640, Pages: C3-C3, ISSN: 0004-6361
  • Journal article
    Ergun RE, Ahmadi N, Kromyda L, Schwartz SJ, Chasapis A, Hoilijoki S, Wilder FD, Stawarz JE, Goodrich KA, Turner DL, Cohen IJ, Bingham ST, Holmes JC, Nakamura R, Pucci F, Torbert RB, Burch JL, Lindqvist P-A, Strangeway RJ, Le Contel O, Giles BLet al., 2020,

    Observations of Particle Acceleration in Magnetic Reconnection-driven Turbulence

    , ASTROPHYSICAL JOURNAL, Vol: 898, ISSN: 0004-637X
  • Journal article
    Ergun RE, Ahmadi N, Kromyda L, Schwartz SJ, Chasapis A, Hoilijoki S, Wilder FD, Cassak PA, Stawarz JE, Goodrich KA, Turner DL, Pucci F, Pouquet A, Matthaeus WH, Drake JF, Hesse M, Shay MA, Torbert RB, Burch JLet al., 2020,

    Particle Acceleration in Strong Turbulence in the Earth's Magnetotail

    , ASTROPHYSICAL JOURNAL, Vol: 898, ISSN: 0004-637X
  • Journal article
    Bowen TA, Bale SD, Bonnell JW, Larson D, Mallet A, McManus MD, Mozer FS, Pulupa M, Vasko IY, Verniero JLet al., 2020,

    The Electromagnetic Signature of Outward Propagating Ion-scale Waves

    , ASTROPHYSICAL JOURNAL, Vol: 899, ISSN: 0004-637X
  • Journal article
    Wilder FD, Schwartz SJ, Ergun RE, Eriksson S, Ahmadi N, Chasapis A, Newman DL, Burch JL, Torbert RB, Strangeway RJ, Giles BLet al., 2020,

    Parallel Electrostatic Waves Associated With Turbulent Plasma Mixing in the Kelvin-Helmholtz Instability

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 47, ISSN: 0094-8276
  • Journal article
    Fujita R, Morimoto S, Maksyutov S, Kim H-S, Arshinov M, Brailsford G, Aoki S, Nakazawa Tet al., 2020,

    Global and Regional CH<sub>4</sub>Emissions for 1995-2013 Derived From Atmospheric CH<sub>4</sub>, δ<SUP>13</SUP>C-CH<sub>4</sub>, and δD-CH<sub>4</sub>Observations and a Chemical Transport Model

    , JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, Vol: 125, ISSN: 2169-897X
  • Journal article
    Gibbins G, Haigh JD, 2020,

    Entropy production rates of the climate

    , Journal of the Atmospheric Sciences, ISSN: 0022-4928

    There is ongoing interest in the global entropy production rate as a climate diagnostic and predictor, but progress has been limited by ambiguities in its definition; different conceptual boundaries of the climate system give rise to different internal production rates. Three viable options are described, estimated and investigated here, two of which -- the material and the total radiative (here `planetary') entropy production rates -- are well-established and a third which has only recently been considered but appears very promising. This new option is labelled the `transfer' entropy production rate and includes all irreversible processes that transfer heat within the climate, radiative and material, but not those involved in the exchange of radiation with space. Estimates in three model climates put the material rate in the range 27-48 mW/m^2K, the transfer rate 67-76mW/m^2K, and the planetary rate 1279-1312 mW/m^2K. The climate-relevance of each rate is probed by calculating their responses to climate changes in a simple radiative-convective model. An increased greenhouse effect causes a significant increase in the material and transfer entropy production rates but has no direct impact on the planetary rate. When the same surface temperature increase is forced by changing the albedo instead, the material and transfer entropy production rates increase less dramatically and the planetary rate also registers an increase. This is pertinent to solar radiation management as it demonstrates the difficulty of reversing greenhouse gas-mediated climate changes by albedo alterations. It is argued that the transfer perspective has particular significance in the climate system and warrants increased prominence.
  • Journal article
    AkhavanTafti M, Palmroth M, Slavin JA, Battarbee M, Ganse U, Grandin M, Le G, Gershman DJ, Eastwood JP, Stawarz JEet al., 2020,

    Comparative analysis of the vlasiator simulations and MMS observations of multiple X‐line reconnection and flux transfer events

    , Journal of Geophysical Research: Space Physics, Vol: 125, Pages: 1-22, ISSN: 2169-9380

    The Vlasiator hybrid‐Vlasov code was developed to investigate global magnetospheric dynamics at ion‐kinetic scales. Here, we focus on the role of magnetic reconnection in the formation and evolution of the magnetic islands at the low‐latitude magnetopause, under southward interplanetary magnetic field (IMF) conditions. The simulation results indicate that: 1) the magnetic reconnection ion kinetics, including the Earthward‐pointing Larmor electric field on the magnetospheric‐side of an X‐point and anisotropic ion distributions, are well‐captured by Vlasiator, thus enabling the study of reconnection‐driven magnetic island evolution processes, 2) magnetic islands evolve due to continuous reconnection at adjacent X‐points, ‘coalescence’ which refers to the merging of neighboring islands to create a larger island, ‘erosion’ during which an island loses magnetic flux due to reconnection, and ‘division’ which involves the splitting of an island into smaller islands, and 3) continuous reconnection at adjacent X‐points is the dominant source of magnetic flux and plasma to the outer layers of magnetic islands resulting in cross‐sectional growth rates up to +0.3 RE2/min. The simulation results are compared to the Magnetospheric Multiscale (MMS) measurements of a chain of ion‐scale flux transfer events (FTEs) sandwiched between two dominant X‐lines. The MMS measurements similarly reveal: 1) anisotropic ion populations, and 2) normalized reconnection rate ~0.18, in agreement with theory and the Vlasiator predictions. Based on the simulation results and the MMS measurements, it is estimated that the observed ion‐scale FTEs may grow Earth‐sized within ~10 minutes, which is comparable to the average transport time for FTEs formed in the subsolar region to the high‐latitude magnetopause. Future simulations shall revisit reconnection‐driven island evolution processes with improved spatial resolutions.
  • Journal article
    Eggington JWB, Eastwood JP, Mejnertsen L, Desai RT, Chittenden JPet al., 2020,

    Dipole tilt effect on magnetopause reconnection and the steady‐state magnetosphere‐ionosphere system: global MHD simulation

    , Journal of Geophysical Research: Space Physics, Vol: 125, Pages: 1-17, ISSN: 2169-9380

    The Earth’s dipole tilt angle changes both diurnally and seasonally and introduces numerous variabilities in the coupled magnetosphere‐ionosphere system. By altering the location and intensity of magnetic reconnection, the dipole tilt influences convection on a global scale. However, due to the nonlinear nature of the system, various other effects like dipole rotation, varying IMF orientation and non‐uniform ionospheric conductance can smear tilt effects arising purely from changes in coupling with the solar wind. To elucidate the underlying tilt angle‐dependence, we perform MHD simulations of the steady‐state magnetosphere‐ionosphere system under purely southward IMF conditions for tilt angles from 0°‐90°. We identify the location of the magnetic separator in each case, and find that an increasing tilt angle shifts the 3‐D X‐line southward on the magnetopause due to changes in magnetic shear angle. The separator is highly unsteady above 50° tilt angle, characteristic of regular FTE generation on the magnetopause. The reconnection rate drops as the tilt angle becomes large, but remains continuous across the dayside such that the magnetosphere is open even for 90°. These trends map down to the ionosphere, with the polar cap contracting as the tilt angle increases, and region‐I field‐aligned current (FAC) migrating to higher latitudes with changing morphology. The tilt introduces a north‐south asymmetry in magnetospheric convection, thus driving more FAC in the northern (sunward‐facing) hemisphere for large tilt angles than in the south independent of conductance. These results highlight the strong sensitivity to onset time in the potential impact of a severe space weather event.
  • Journal article
    Hantson S, Kelley DI, Arneth A, Harrison SP, Archibald S, Bachelet D, Forrest M, Hickler T, Lasslop G, Li F, Mangeon S, Melton JR, Nieradzik L, Rabin SS, Prentice IC, Sheehan T, Sitch S, Teckentrup L, Voulgarakis A, Yue Cet al., 2020,

    Quantitative assessment of fire and vegetation properties in simulations with fire-enabled vegetation models from the Fire Model Intercomparison Project

    , Geoscientific Model Development, Vol: 13, Pages: 3299-3318, ISSN: 1991-959X

    Global fire-vegetation models are widely used to assess impacts of environmental change on fire regimes and the carbon cycle and to infer relationships between climate, land use and fire. However, differences in model structure and parameterizations, in both the vegetation and fire components of these models, could influence overall model performance, and to date there has been limited evaluation of how well different models represent various aspects of fire regimes. The Fire Model Intercomparison Project (FireMIP) is coordinating the evaluation of state-of-the-art global fire models, in order to improve projections of fire characteristics and fire impacts on ecosystems and human societies in the context of global environmental change. Here we perform a systematic evaluation of historical simulations made by nine FireMIP models to quantify their ability to reproduce a range of fire and vegetation benchmarks. The FireMIP models simulate a wide range in global annual total burnt area (39–536 Mha) and global annual fire carbon emission (0.91–4.75 Pg C yr−1) for modern conditions (2002–2012), but most of the range in burnt area is within observational uncertainty (345–468 Mha). Benchmarking scores indicate that seven out of nine FireMIP models are able to represent the spatial pattern in burnt area. The models also reproduce the seasonality in burnt area reasonably well but struggle to simulate fire season length and are largely unable to represent interannual variations in burnt area. However, models that represent cropland fires see improved simulation of fire seasonality in the Northern Hemisphere. The three FireMIP models which explicitly simulate individual fires are able to reproduce the spatial pattern in number of fires, but fire sizes are too small in key regions, and this results in an underestimation of burnt area. The correct representation of spatial and seasonal patterns in vegetation appears
  • Journal article
    Tang T, Shindell D, Zhang Y, Voulgarakis A, Lamarque J-F, Myhre G, Stjern CW, Faluvegi G, Samset BHet al., 2020,

    Response of surface shortwave cloud radiative effect to greenhouse gases and aerosols and its impact on summer maximum temperature

    , Atmospheric Chemistry and Physics, Vol: 20, Pages: 8251-8266, ISSN: 1680-7316

    Shortwave cloud radiative effects (SWCREs), defined as the difference of the shortwave radiative flux between all-sky and clear-sky conditions at the surface, have been reported to play an important role in influencing the Earth's energy budget and temperature extremes. In this study, we employed a set of global climate models to examine the SWCRE responses to CO2, black carbon (BC) aerosols, and sulfate aerosols in boreal summer over the Northern Hemisphere. We found that CO2 causes positive SWCRE changes over most of the NH, and BC causes similar positive responses over North America, Europe, and eastern China but negative SWCRE over India and tropical Africa. When normalized by effective radiative forcing, the SWCRE from BC is roughly 3–5 times larger than that from CO2. SWCRE change is mainly due to cloud cover changes resulting from changes in relative humidity (RH) and, to a lesser extent, changes in cloud liquid water, circulation, dynamics, and stability. The SWCRE response to sulfate aerosols, however, is negligible compared to that for CO2 and BC because part of the radiation scattered by clouds under all-sky conditions will also be scattered by aerosols under clear-sky conditions. Using a multilinear regression model, it is found that mean daily maximum temperature (Tmax) increases by 0.15 and 0.13 K per watt per square meter (W m−2) increase in local SWCRE under the CO2 and BC experiment, respectively. When domain-averaged, the contribution of SWCRE change to summer mean Tmax changes was 10 %–30 % under CO2 forcing and 30 %–50 % under BC forcing, varying by region, which can have important implications for extreme climatic events and socioeconomic activities.
  • Journal article
    Saunois M, Stavert AR, Poulter B, Bousquet P, Canadell JG, Jackson RB, Raymond PA, Dlugokencky EJ, Houweling S, Patra PK, Ciais P, Arora VK, Bastviken D, Bergamaschi P, Blake DR, Brailsford G, Bruhwiler L, Carlson KM, Carrol M, Castaldi S, Chandra N, Crevoisier C, Crill PM, Covey K, Curry CL, Etiope G, Frankenberg C, Gedney N, Hegglin M, Hoglund-Isaksson L, Hugelius G, Ishizawa M, Ito A, Janssens-Maenhout G, Jensen KM, Joos F, Kleinen T, Krummel PB, Langenfelds RL, Laruelle GG, Liu L, Machida T, Maksyutov S, McDonald KC, McNorton J, Miller PA, Melton JR, Morino I, Muller J, Murguia-Flores F, Naik V, Niwa Y, Noce S, Doherty SO, Parker RJ, Peng C, Peng S, Peters GP, Prigent C, Prinn R, Ramonet M, Regnier P, Riley WJ, Rosentreter JA, Segers A, Simpson IJ, Shi H, Smith SJ, Steele LP, Thornton BF, Tian H, Tohjima Y, Tubiello FN, Tsuruta A, Viovy N, Voulgarakis A, Weber TS, van Weele M, van der Werf GR, Weiss RF, Worthy D, Wunch D, Yin Y, Yoshida Y, Zhang W, Zhang Z, Zhao Y, Zheng B, Zhu Q, Zhu Q, Zhuang Qet al., 2020,

    The global methane budget 2000-2017

    , Earth System Science Data, Vol: 12, Pages: 1561-1623, ISSN: 1866-3508

    Understanding and quantifying the global methane (CH4) budget is important for assessing realistic pathways to mitigate climate change. Atmospheric emissions and concentrations of CH4 continue to increase, making CH4 the second most important human-influenced greenhouse gas in terms of climate forcing, after carbon dioxide (CO2). The relative importance of CH4 compared to CO2 depends on its shorter atmospheric lifetime, stronger warming potential, and variations in atmospheric growth rate over the past decade, the causes of which are still debated. Two major challenges in reducing uncertainties in the atmospheric growth rate arise from the variety of geographically overlapping CH4 sources and from the destruction of CH4 by short-lived hydroxyl radicals (OH). To address these challenges, we have established a consortium of multidisciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate new research aimed at improving and regularly updating the global methane budget. Following Saunois et al. (2016), we present here the second version of the living review paper dedicated to the decadal methane budget, integrating results of top-down studies (atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up estimates (including process-based models for estimating land surface emissions and atmospheric chemistry, inventories of anthropogenic emissions, and data-driven extrapolations).For the 2008–2017 decade, global methane emissions are estimated by atmospheric inversions (a top-down approach) to be 576 Tg CH4 yr−1 (range 550–594, corresponding to the minimum and maximum estimates of the model ensemble). Of this total, 359 Tg CH4 yr−1 or ∼ 60 % is attributed to anthropogenic sources, that is emissions caused by direct human activity (i.e. anthropogenic emissions; range 336–376 Tg CH4 yr−1 or
  • Journal article
    Milillo, Fujimoto, Murakami, Benkhoff, Zender, Aizawa, Dósa, Griton, Heyner, Ho, Imber, Jia, Karlsson, Killen, Laurenza, Lindsay, McKenna-Lawlor, Mura, Raines, Rothery, André, Baumjohann, Berezhnoy, Bourdin, Bunce, Califano, Deca, de la Fuente, Dong, Grava, Fatemi, Henri, Ivanovski, Jackson, James, Kallio, Kasaba, Kilpua, Kobayashi, Langlais, Leblanc, Lhotka, Mangano, Martindale, Massetti, Masters A, Morooka, Narita, Oliveira, Odstrcil, Orsini, Pelizzo, Plainaki, Plaschke, Sahraoui, Seki, Slavin, Vainio, Wurz, Barabash, Carr C, Delcourt, Glassmeier, Grande, Hirahara, Huovelin, Korablev, Kojima, Lichtenegger, Livi, Matsuoka, Moissl, Moncuquet, Muinonen, Quèmerais, Saito, Yagitani, Yoshikawa, Wahlundet al., 2020,

    Investigating Mercury’s environment with the two-spacecraft BepiColombo mission

    , Space Science Reviews, Vol: 216, Pages: 1-78, ISSN: 0038-6308

    The ESA-JAXA BepiColombo mission will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric dynamics at Mercury as well as their interactions with the solar wind, radiation, and interplanetary dust. Many scientific instruments onboard the two spacecraft will be completely, or partially devoted to study the near-space environment of Mercury as well as the complex processes that govern it. Many issues remain unsolved even after the MESSENGER mission that ended in 2015. The specific orbits of the two spacecraft, MPO and Mio, and the comprehensive scientific payload allow a wider range of scientific questions to be addressed than those that could be achieved by the individual instruments acting alone, or by previous missions. These joint observations are of key importance because many phenomena in Mercury’s environment are highly temporally and spatially variable. Examples of possible coordinated observations are described in this article, analysing the required geometrical conditions, pointing, resolutions and operation timing of different BepiColombo instruments sensors.
  • Journal article
    Stawarz JE, Matteini L, Parashar TN, Franci L, Eastwood JP, Gonzalez CA, Gingell I, Burch JL, Ergun RE, Ahmadi N, Giles BL, Gershman DJ, Le Contel O, Lindqvist P-A, Russell CT, Strangeway RJ, Torbert RBet al., 2020,

    Generalized Ohm's Law Decomposition of the Electric Field in Magnetosheath Turbulence: Magnetospheric Multiscale Observations
  • Journal article
    Liu TZ, Hietala H, Angelopoulos V, Omelchenko Y, Vainio R, Plaschke Fet al., 2020,

    Statistical study of magnetosheath jet‐driven bow waves

    , Journal of Geophysical Research: Space Physics, Vol: 125, Pages: 1-14, ISSN: 2169-9380

    When a magnetosheath jet (localized dynamic pressure enhancements) compresses ambient magnetosheath at a (relative) speed faster than the local magnetosonic speed, a bow wave or shock can form ahead of the jet. Such bow waves or shocks were recently observed to accelerate particles, thus contributing to magnetosheath heating and particle acceleration in the extended environment of Earth’s bow shock. To further understand the characteristics of jet‐driven bow waves, we perform a statistical study to examine which solar wind conditions favor their formation and whether it is common for them to accelerate particles. We identified 364 out of 2859 (~13%) magnetosheath jets to have a bow wave or shock ahead of them with Mach number typically larger than 1.1. We show that large solar wind plasma beta, weak interplanetary magnetic field (IMF) strength, large solar wind Alfvén Mach number, and strong solar wind dynamic pressure present favorable conditions for their formation. We also show that magnetosheath jets with bow waves or shocks are more frequently associated with higher maximum ion and electron energies than those without them, confirming that it is common for these structures to accelerate particles. In particular, magnetosheath jets with bow waves have electron energy flux enhanced on average by a factor of 2 compared to both those without bow waves and the ambient magnetosheath. Our study implies that magnetosheath jets can contribute to shock acceleration of particles especially for high Mach number shocks. Therefore, shock models should be generalized to include magnetosheath jets and concomitant particle acceleration.
  • Journal article
    Liu TZ, Hietala H, Angelopoulos V, Vainio R, Omelchenko Yet al., 2020,

    Electron acceleration by magnetosheath jet‐driven bow waves

    , Journal of Geophysical Research: Space Physics, Vol: 125, Pages: 1-13, ISSN: 2169-9380

    Magnetosheath jets are localized fast flows with enhanced dynamic pressure. When they supermagnetosonically compress the ambient magnetosheath plasma, a bow wave or shock can form ahead of them. Such a bow wave was recently observed to accelerate ions and possibly electrons. The ion acceleration process was previously analyzed, but the electron acceleration process remains largely unexplored. Here we use multi‐point observations by Time History of Events and Macroscale during Substorms from three events to determine whether and how magnetosheath jet‐driven bow waves can accelerate electrons. We show that when suprathermal electrons in the ambient magnetosheath convect towards a bow wave, some electrons are shock‐drift accelerated and reflected towards the ambient magnetosheath and others continue moving downstream of the bow wave resulting in bi‐directional motion. Our study indicates that magnetosheath jet‐driven bow waves can result in additional energization of suprathermal electrons in the magnetosheath. It implies that magnetosheath jets can increase the efficiency of electron acceleration at planetary bow shocks or other similar astrophysical environments.
  • Journal article
    Bowen TA, Mallet A, Bale SD, Bonnell JW, Case AW, Chandran BDG, Chasapis A, Chen CHK, Duan D, de Wit TD, Goetz K, Halekas JS, Harvey PR, Kasper JC, Korreck KE, Larson D, Livi R, MacDowall RJ, Malaspina DM, McManus MD, Pulupa M, Stevens M, Whittlesey Pet al., 2020,

    Constraining Ion-Scale Heating and Spectral Energy Transfer in Observations of Plasma Turbulence

    , PHYSICAL REVIEW LETTERS, Vol: 125, ISSN: 0031-9007
  • Journal article
    Martin CJ, Ray LC, Constable DA, Southwood DJ, Lorch CTS, Felici Met al., 2020,

    Evaluating the ionospheric mass source for Jupiter's magnetosphere: An ionospheric outflow model for the auroral regions

    , Journal of Geophysical Research: Space Physics, Vol: 125, ISSN: 2169-9380

    Ionospheric outflow is the flow of plasma initiated by a loss of equilibrium along a magnetic field line which induces an ambipolar electric field due to the separation of electrons and ions in a gravitational field and other mass dependant sources. We have developed an ionospheric outflow model using the transport equations to determine the number of particles that flow into the outer magnetosphere of Jupiter. The model ranges from 1400 km in altitude above the 1 bar level to 2.5 RJ along the magnetic field line and considers H+ and H3+ as the main ion constituents. Previously, only pressure gradients and gravitational forces were considered in modelling polar wind. However, at Jupiter we need to evaluate the affect of field‐aligned currents present in the auroral regions due to the breakdown of corotation in the magnetosphere, along with the centrifugal force exerted on the particles due to the fast planetary rotation rate. The total number flux from both hemispheres is found to be 1.3‐1.8 x 1028 s‐1 comparable in total number flux to the Io plasma source. The mass flux is lower due to the difference in ion species. This influx of protons from the ionosphere into the inner and middle magnetosphere needs to be included in future assessments of global flux tube dynamics and composition of the magnetosphere system.
  • Journal article
    Cao H, Dougherty MK, Hunt GJ, Provan G, Cowley SWH, Bunce EJ, Kellock S, Stevenson DJet al., 2020,

    The landscape of Saturn's internal magnetic field from the Cassini Grand Finale

    , ICARUS, Vol: 344, ISSN: 0019-1035

This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.

Request URL: http://www.imperial.ac.uk:80/respub/WEB-INF/jsp/search-t4-html.jsp Request URI: /respub/WEB-INF/jsp/search-t4-html.jsp Query String: id=214&limit=30&page=29&respub-action=search.html Current Millis: 1732346244752 Current Time: Sat Nov 23 07:17:24 GMT 2024

Useful Links