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  • Journal article
    Galand M, Feldman PD, Bockelee-Morvan D, Biver N, Cheng Y-C, Rinaldi G, Rubin M, Altwegg K, Deca J, Beth A, Stephenson P, Heritier K, Henri P, Parker JW, Carr C, Eriksson AI, Burch Jet al., 2020,

    Far-ultraviolet aurora identified at comet 67P/ Churyumov-Gerasimenko

    , Nature Astronomy, Vol: 4, Pages: 1084-1091, ISSN: 2397-3366

    Having a nucleus darker than charcoal, comets are usually detected from Earth through the emissions from their coma. The coma is an envelope of gas that forms through the sublimation of ices from the nucleus as the comet gets closer to the Sun. In the far-ultraviolet portion of the spectrum, observations of comae have revealed the presence of atomic hydrogen and oxygen emissions. When observed over large spatial scales as seen from Earth, such emissions are dominated by resonance fluorescence pumped by solar radiation. Here, we analyse atomic emissions acquired close to the cometary nucleus by the Rosetta spacecraft and reveal their auroral nature. To identify their origin, we undertake a quantitative multi-instrument analysis of these emissions by combining coincident neutral gas, electron and far-ultraviolet observations. We establish that the atomic emissions detected from Rosetta around comet 67P/Churyumov-Gerasimenko at large heliocentric distances result from the dissociative excitation of cometary molecules by accelerated solar-wind electrons (and not by electrons produced from photo-ionization of cometary molecules). Like the discrete aurorae at Earth and Mars, this cometary aurora is driven by the interaction of the solar wind with the local environment. We also highlight how the oxygen line O I at wavelength 1,356 Å could be used as a tracer of solar-wind electron variability.
  • Conference paper
    Southwood D, Cao H, Hunt G, Shebanits O, Dougherty Met al., 2020,

    Discovery of Alfven waves planetward of the Rings of Saturn

    , Europlanet Science Congress 2020, Publisher: American Geophysical Union

    Between April and September 2017 in the final stages of the Cassini Saturn Orbiter mission the spacecraft executed 22 orbits passing planetward of the innermost ring, the D-ring. During periapsis passes on all these orbits oscillations were detected in the azimuthal magnetic field components on typical time scales from a few minutes to 10 minutes. We argue that the time-varying signals detected on the spacecraft are also primarily time-varying in the plasma frame. Nonetheless, we show that nearly all signals exhibit a distinct spatial effect, namely a magnetic node near the effective field line equator. The oscillations thus have a standing structure along the background magnetic field and it follows that they are field line resonances associated with Alfvén waves. The form of the signals suggests that the local field line resonances are most likely pumped from global sources. This is the first detection in a giant planet magnetosphere of a phenomenon known to be important at Earth.
  • Journal article
    Kilpua EKJ, Fontaine D, Good SW, Ala-Lahti M, Osmane A, Palmerio E, Yordanova E, Moissard C, Hadid LZ, Janvier Met al., 2020,

    Magnetic field fluctuation properties of coronal mass ejection-driven sheath regions in the near-Earth solar wind

    , ANNALES GEOPHYSICAE, Vol: 38, Pages: 999-1017, ISSN: 0992-7689
  • Journal article
    Greaves J, Richards A, Bains W, Rimmer P, Sagawa H, Clements D, Seager S, Petkowski J, Sousa-Silva C, Ranjan S, Drabek-Maunder E, Fraser H, Cartwright A, Muller-Wodarg I, Zhan Z, Friberg P, Coulson I, Lee E, Hoge Jet al., 2020,

    Phosphine gas in the cloud decks of Venus

    , Nature Astronomy, Vol: 5, Pages: 655-664, ISSN: 2397-3366

    Measurements of trace gases in planetary atmospheres help us explore chemical conditions different to those on Earth. Our nearest neighbour, Venus, has cloud decks that are temperate but hyperacidic. Here we report the apparent presence of phosphine (PH3) gas in Venus’s atmosphere, where any phosphorus should be in oxidized forms. Single-line millimetre-waveband spectral detections (quality up to ~15σ) from the JCMT and ALMA telescopes have no other plausible identification. Atmospheric PH3 at ~20 ppb abundance is inferred. The presence of PH3 is unexplained after exhaustive study of steady-state chemistry and photochemical pathways, with no currently known abiotic production routes in Venus’s atmosphere, clouds, surface and subsurface, or from lightning, volcanic or meteoritic delivery. PH3 could originate from unknown photochemistry or geochemistry, or, by analogy with biological production of PH3 on Earth, from the presence of life. Other PH3 spectral features should be sought, while in situ cloud and surface sampling could examine sources of this gas.
  • Journal article
    Williams RG, Ceppi P, Katavouta A, 2020,

    Controls of the transient climate response to emissions by physical feedbacks, heat uptake and carbon cycling

    , Environmental Research Letters, Vol: 15, ISSN: 1748-9326

    The surface warming response to carbon emissions is diagnosed using a suite of Earth system models, 9 CMIP6 and 7 CMIP5, following an annual 1\% rise in atmospheric CO$_2$ over 140 years. This surface warming response defines a climate metric, the Transient Climate Response to cumulative carbon Emissions (TCRE), which is important in estimating how much carbon may be emitted to avoid dangerous climate. The processes controlling these intermodel differences in the TCRE are revealed by defining the TCRE in terms of a product of three dependences: the surface warming dependence on radiative forcing (including the effects of physical climate feedbacks and planetary heat uptake), the radiative forcing dependence on changes in atmospheric carbon and the airborne fraction. Intermodel differences in the TCRE are mainly controlled by the thermal response involving the surface warming dependence on radiative forcing, which arise through large differences in physical climate feedbacks that are only partly compensated by smaller differences in ocean heat uptake. The other contributions to the TCRE from the radiative forcing and carbon responses are of comparable importance to the contribution from the thermal response on timescales of 50 years and longer for our subset of CMIP5 models and 100 years and longer for our subset of CMIP6 models. Hence, providing tighter constraints on how much carbon may be emitted based on the TCRE requires providing tighter bounds for estimates of the physical climate feedbacks, particularly from clouds, as well as to a lesser extent for the other contributions from the rate of ocean heat uptake, and the terrestrial and ocean cycling of carbon.
  • Journal article
    Zhang YC, Dai L, Rong ZJ, Wang C, Rème H, Dandouras I, Carr CM, Escoubet CPet al., 2020,

    Observation of the large‐amplitude and fast‐damped plasma sheet flapping triggered by reconnection‐induced ballooning instability

    , Journal of Geophysical Research: Space Physics, Vol: 125, Pages: 1-11, ISSN: 2169-9380

    In this study, we reported the large‐amplitude and fast‐damped flapping of the plasma sheet, which co‐occurred with magnetic reconnection. Data from the Double Star TC‐1 and Cluster satellites were used to analyze the features of the plasma sheet flapping 1.4 RE earthward of an ongoing magnetic reconnection event. The flapping was rapidly damped, and its amplitude decreased from the magnetohydrodynamics scale to the subion scale in 5 min. The variation in the flapping period (from 224 to 20 s) indicated that the source of the flapping had highly dynamic temporal characteristics. The plasma sheet flapping propagated duskward through a kink‐like wave with a velocity of 100 km/s, which was in agreement with the group velocity of the ballooning perturbation. A correlation analysis between the magnetic reconnection and plasma sheet flapping indicated that the magnetic reconnection likely facilitated the occurrence of ballooning instability by altering the state of plasma in the downstream plasma sheet. In this regard, the reconnection‐induced ballooning instability could be a potential mechanism to generate the flapping motion of the plasma sheet.
  • Journal article
    Brown Z, Koskinen T, Muller-Wodarg I, West R, Jouchoux A, Esposito Let al., 2020,

    A pole-to-pole pressure-temperature map of Saturn's thermosphere from Cassini Grand Finale data

    , Nature Astronomy, Vol: 4, Pages: 872-879, ISSN: 2397-3366

    Temperatures of the outer planet thermospheres exceed those predicted by solar heating alone by several hundred degrees. Enough energy is deposited at auroral regions to heat the entire thermosphere, but models predict that equatorward distribution is inhibited by strong Coriolis forces and ion drag1,2. A better understanding of auroral energy deposition and circulation are critical to solving this so-called energy crisis. Stellar occultations observed by the Ultraviolet Imaging Spectrograph instrument during the Cassini Grand Finale were designed to map the thermosphere from pole to pole. We analyse these observations, together with earlier observations from 2016 and 2017, to create a two-dimensional map of densities and temperatures in Saturn’s thermosphere as a function of latitude and depth. The observed temperatures at auroral latitudes are cooler and peak at higher altitudes and lower latitudes than predicted by models, leading to a shallower meridional pressure gradient. Under modified geostrophy3, we infer slower westward zonal winds that extend to lower latitudes than predicted, supporting equatorward flow from approximately 70° to 30° latitude in both hemispheres. We also show evidence of atmospheric waves in the data that can contribute to equatorward redistribution of energy through zonal drag.
  • Journal article
    Mozer FS, Agapitov OV, Bale SD, Bonnell JW, Bowen TA, Vasko Iet al., 2020,

    DC and Low-Frequency Electric Field Measurements on the Parker Solar Probe

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 125, ISSN: 2169-9380
  • Journal article
    Bradley TJ, Cowley SWH, Bunce EJ, Melin H, Provan G, Nichols JD, Dougherty MK, Roussos E, Krupp N, Tao C, Lamy L, Pryor WR, Hunt GJet al., 2020,

    Saturn's Nightside Dynamics During Cassini's F Ring and Proximal Orbits: Response to Solar Wind and Planetary Period Oscillation Modulations

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 125, ISSN: 2169-9380
  • Journal article
    Lotekar A, Vasko IY, Mozer FS, Hutchinson I, Artemyev AV, Bale SD, Bonnell JW, Ergun R, Giles B, Khotyaintsev YV, Lindqvist P-A, Russell CT, Strangeway Ret al., 2020,

    Multisatellite MMS Analysis of Electron Holes in the Earth's Magnetotail: Origin, Properties, Velocity Gap, and Transverse Instability

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 125, ISSN: 2169-9380
  • Journal article
    Ala-Lahti M, Ruohotie J, Good S, Kilpua EKJ, Lugaz Net al., 2020,

    Spatial Coherence of Interplanetary Coronal Mass Ejection Sheaths at 1 AU

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 125, ISSN: 2169-9380
  • 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.

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