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  • Journal article
    Masters A, 2017,

    Model-based assessments of magnetic reconnection and Kelvin-Helmholtz instability at Jupiter’s magnetopause

    , Journal of Geophysical Research: Space Physics, Vol: 122, Pages: 11154-11174, ISSN: 2169-9380

    The interaction between the solar wind and Jupiter's magnetic field confines the planetary field to the largest magnetosphere in the Solar System. However, the full picture of when and where key processes operate at the magnetopause boundary of the system remains unclear. This is essential for testing understanding with observations and for determining the relative importance of different drivers of Jovian magnetospheric dynamics. Here we present a global analytical model of Jovian magnetopause conditions under steady state, which forms the basis of boundary process assessments. Sites of magnetic reconnection at Jupiter's magnetopause are expected to be in regions of sufficiently high magnetic shear across the boundary, controlled by the orientation of the interplanetary magnetic field. Reconnection rates are also most sensitive to changes in the highly variable IMF, followed by changes in the solar wind plasma mass density. The largest plasma flow shear across the boundary is in the equatorial dawn region, producing a region that is typically unstable to growth of the Kelvin-Helmholtz (K-H) instability. Compared to magnetopause reconnection site locations, this K-H-unstable region at dawn is less sensitive to changing conditions. Motion of K-H boundary perturbations typically includes dawn-to-dusk motion across the subsolar region. Model-predicted reconnection voltages are typically hundreds of kV but rely on steady solar wind conditions on a time scale that is longer than typical at Jupiter's orbit. How the reconnection voltage compares to the voltage applied due to the “viscous-like” interaction involving K-H instability remains unclear.
  • Journal article
    Kajdic P, Hietala H, Blanco-Cano X, 2017,

    Different Types of Ion Populations Upstream of the 2013 October 8 Interplanetary Shock

    , ASTROPHYSICAL JOURNAL LETTERS, Vol: 849, ISSN: 2041-8205
  • Journal article
    Kasper JC, Klein KG, Weber T, Maksimovic M, Zaslavsky A, Bale SD, Maruca BA, Stevens ML, Case AWet al., 2017,

    A Zone of Preferential Ion Heating Extends Tens of Solar Radii from the Sun

    , ASTROPHYSICAL JOURNAL, Vol: 849, ISSN: 0004-637X
  • Journal article
    Wang S, Fu G, Pang H, 2017,

    Structure Analyses of the Explosive Extratropical Cyclone: A Case Study over the Northwestern Pacific in March 2007

    , Journal of Ocean University of China (English Edition), Vol: 16, Pages: 933-944, ISSN: 1671-2463

    The synoptic situation and mesoscale structure of an explosive extratropical cyclone over the Northwestern Pacific in March 2007 are investigated through weather station observations and data reanalysis. The cyclone is located beneath the poleward side of the exit of a 200 hPa jet, which is a strong divergent region aloft. At mid-level, the cyclone lies on the downstream side of a well-developed trough, where a strong ascending motion frequently occurs. Cross-section analyses with weather station data show that the cyclone has a warm and moist core. A ‘nose’ of the cold front, which is characterized by a low-level protruding structure in the equivalent potential temperature field, forms when the cyclone moves offshore. This ‘nose’ structure is hypothesized to have been caused by the heating effect of the Kuroshio Current. Two low-level jet streams are also identified on the western and eastern sides of the cold front. The western jet conveys cold and dry air at 800–900 hPa. The wind in the northern part is northeasterly, and the wind in the southern part is northwesterly. By contrast, the eastern jet carries warm and moist air into the cyclone system, ascending northward from 900 hPa to 600–700 hPa. The southern part is dominated by the southerly wind, and the wind in the northern part is southwesterly. The eastern and western jets significantly increase the air temperature and moisture contrast in the vicinity of the cold front. This increase could play an important role in improving the rapid cyclogenesis process.
  • Journal article
    Stjern CW, Samset BH, Myhre G, Forster PM, Hodnebrog Ø, Andrews T, Boucher O, Faluvegi G, Iversen T, Kasoar M, Kharin V, Kirkevåg A, Lamarque J-F, Olivié D, Richardson T, Shawki D, Shindell D, Smith CJ, Takemura T, Voulgarakis Aet al., 2017,

    Rapid Adjustments Cause Weak Surface Temperature Response to Increased Black Carbon Concentrations

    , Journal of Geophysical Research: Atmospheres, Vol: 122, Pages: 462-481, ISSN: 2169-897X

    We investigate the climate response to increased concentrations of black carbon (BC), as part of the Precipitation Driver Response Model Intercomparison Project (PDRMIP). A tenfold increase in BC is simulated by nine global coupled-climate models, producing a model median effective radiative forcing of 0.82 (ranging from 0.41 to 2.91) W m−2, and a warming of 0.67 (0.16 to 1.66) K globally and 1.24 (0.26 to 4.31) K in the Arctic. A strong positive instantaneous radiative forcing (median of 2.10 W m−2 based on five of the models) is countered by negative rapid adjustments (−0.64 W m−2 for the same five models), which dampen the total surface temperature signal. Unlike other drivers of climate change, the response of temperature and cloud profiles to the BC forcing is dominated by rapid adjustments. Low-level cloud amounts increase for all models, while higher-level clouds are diminished. The rapid temperature response is particularly strong above 400 hPa, where increased atmospheric stabilization and reduced cloud cover contrast the response pattern of the other drivers. In conclusion, we find that this substantial increase in BC concentrations does have considerable impacts on important aspects of the climate system. However, some of these effects tend to offset one another, leaving a relatively small median global warming of 0.47 K per W m−2—about 20% lower than the response to a doubling of CO2. Translating the tenfold increase in BC to the present-day impact of anthropogenic BC (given the emissions used in this work) would leave a warming of merely 0.07 K.
  • Journal article
    Omidi N, Sulaiman AH, Kurth W, Madanian H, Cravens T, Sergis N, Dougherty MK, Edberg NJTet al., 2017,

    A Single Deformed Bow Shock for Titan-Saturn System

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 122, Pages: 11058-11075, ISSN: 2169-9380

    During periods of high solar wind pressure, Saturn’s bow shock is pushed inside Titan’s orbitexposing the moon and its ionosphere to the solar wind. The Cassini spacecraft’s T96 encounter with Titanoccurred during such a period and showed evidence for shocks associated with Saturn and Titan. It alsorevealed the presence of two foreshocks: one prior to the closest approach (foreshock 1) and one after(foreshock 2). Using electromagnetic hybrid (kinetic ions and fluid electrons) simulations and Cassiniobservations,we showthat the origin of foreshock 1 is tied to the formation of a single deformed bow shock forthe Titan-Saturn system. We also report the observations of a structure in foreshock 1 with properties consistentwith those of spontaneous hot flow anomalies formed in the simulations and previously observed at Earth,Venus, and Mars. The results of hybrid simulations also show the generation of oblique fast magnetosonicwaves upstream of the outbound Titan bow shock in agreement with the observations of large-amplitudemagnetosonic pulsations in foreshock 2. We also discuss the implications of a single deformed bow shock fornew particle acceleration mechanisms and also Saturn’s magnetopause and magnetosphere.
  • Journal article
    Hajra R, Henri P, Vallières X, Galand M, Héritier K, Eriksson AI, Odelstad E, Edberg NJT, Burch JL, Broiles T, Goldstein R, Glassmeier KH, Richter I, Goetz C, Tsurutani BT, Nilsson H, Altwegg K, Rubin Met al., 2017,

    Impact of a cometary outburst on its ionosphere: Rosetta Plasma Consortium observations of the outburst exhibited by comet 67P/Churyumov-Gerasimenko on 19 February 2016

    , Astronomy and Astrophysics, Vol: 607, Pages: 1-10, ISSN: 0004-6361

    We present a detailed study of the cometary ionospheric response to a cometary brightness outburst using in situ measurements for the first time. The comet 67P/Churyumov-Gerasimenko (67P) at a heliocentric distance of 2.4 AU from the Sun, exhibited an outburst at ∼1000 UT on 19 February 2016, characterized by an increase in the coma surface brightness of two orders of magnitude. The Rosetta spacecraft monitored the plasma environment of 67P from a distance of 30 km, orbiting with a relative speed of ∼0.2 m s-1. The onset of the outburst was preceded by pre-outburst decreases in neutral gas density at Rosetta, in local plasma density, and in negative spacecraft potential at ∼0950 UT. In response to the outburst, the neutral density increased by a factor of ∼1.8 and the local plasma density increased by a factor of ∼3, driving the spacecraft potential more negative. The energetic electrons (tens of eV) exhibited decreases in the flux of factors of ∼2 to 9, depending on the energy of the electrons. The local magnetic field exhibited a slight increase in amplitude (~5 nT) and an abrupt rotation (∼36.4°) in response to the outburst. A weakening of 10-100 mHz magnetic field fluctuations was also noted during the outburst, suggesting alteration of the origin of the wave activity by the outburst. The plasma and magnetic field effects lasted for about 4 h, from ∼1000 UT to 1400 UT. The plasma densities are compared with an ionospheric model. This shows that while photoionization is the main source of electrons, electron-impact ionization and a reduction in the ion outflow velocity need to be accounted for in order to explain the plasma density enhancement near the outburst peak.
  • Journal article
    Kilpua EKJ, Balogh A, von Steiger R, Liu YDet al., 2017,

    Geoeffective Properties of Solar Transients and Stream Interaction Regions

    , SPACE SCIENCE REVIEWS, Vol: 212, Pages: 1271-1314, ISSN: 0038-6308
  • Journal article
    Gombosi TI, Baker DN, Balogh A, Erickson PJ, Huba JD, Lanzerotti LJet al., 2017,

    Anthropogenic Space Weather

    , SPACE SCIENCE REVIEWS, Vol: 212, Pages: 985-1039, ISSN: 0038-6308
  • Journal article
    Koskinen HEJ, Baker DN, Balogh A, Gombosi T, Veronig A, von Steiger Ret al., 2017,

    Achievements and Challenges in the Science of Space Weather

    , SPACE SCIENCE REVIEWS, Vol: 212, Pages: 1137-1157, ISSN: 0038-6308
  • Journal article
    Belmonte MT, Pickering JC, Ruffoni MP, Den Hartog EA, Lawler JE, Guzman A, Heiter Uet al., 2017,

    Fe I Oscillator Strengths for Transitions from High-lying Odd-parity Levels

    , Astrophysical Journal, Vol: 848, ISSN: 0004-637X

    We report new experimental Fe I oscillator strengths obtained by combining measurements of branching fractionsmeasured with a Fourier Transform spectrometer and time-resolved, laser-induced fluorescence lifetimes. Thisstudy covers the spectral region ranging from 213 to 1033 nm. A total of 120 experimental log( ) gf -values comingfrom 15 odd-parity energy levels are provided, 22 of which have not been reported previously and 63 of whichhave values with lower uncertainty than the existing data. The radiative lifetimes for 60 upper energy levels arepresented, 39 of which have no previous measurements.
  • Journal article
    Shawki D, Field RD, Tippett MK, Saharjo BH, Albar I, Atmoko D, Voulgarakis Aet al., 2017,

    Long-Lead Prediction of the 2015 Fire and Haze Episode in Indonesia

    , Geophysical Research Letters, Vol: 44, Pages: 9996-10005, ISSN: 0094-8276

    We conducted a case study of National Centers for Environmental Prediction Climate Forecast System version 2 seasonal model forecast performance over Indonesia in predicting the dry conditions in 2015 that led to severe fire, in comparison to the non-El Niño dry season conditions of 2016. Forecasts of the Drought Code (DC) component of Indonesia's Fire Danger Rating System were examined across the entire equatorial Asia region and for the primary burning regions within it. Our results show that early warning lead times of high observed DC in September and October 2015 varied considerably for different regions. High DC over Southern Kalimantan and Southern New Guinea were predicted with 180 day lead times, whereas Southern Sumatra had lead times of up to only 60 days, which we attribute to the absence in the forecasts of an eastward decrease in Indian Ocean sea surface temperatures. This case study provides the starting point for longer-term evaluation of seasonal fire danger rating forecasts over Indonesia.
  • Journal article
    Ball WT, Alsing J, Mortlock DJ, Rozanov EV, Tummon F, Haigh JDet al., 2017,

    Reconciling differences in stratospheric ozone composites

    , Atmospheric Chemistry and Physics, Vol: 17, Pages: 12269-12302, ISSN: 1680-7316

    Observations of stratospheric ozone from multipleinstruments now span three decades; combining these intocomposite datasets allows long-term ozone trends to be estimated.Recently, several ozone composites have been published,but trends disagree by latitude and altitude, even betweencomposites built upon the same instrument data. Weconfirm that the main causes of differences in decadal trendestimates lie in (i) steps in the composite time series when theinstrument source data changes and (ii) artificial sub-decadaltrends in the underlying instrument data. These artefacts introducefeatures that can alias with regressors in multiple linearregression (MLR) analysis; both can lead to inaccuratetrend estimates. Here, we aim to remove these artefacts usingBayesian methods to infer the underlying ozone time seriesfrom a set of composites by building a joint-likelihoodfunction using a Gaussian-mixture density to model outliersintroduced by data artefacts, together with a data-driven prioron ozone variability that incorporates knowledge of problemsduring instrument operation. We apply this Bayesianself-calibration approach to stratospheric ozone in 10◦ bandsfrom 60◦ S to 60◦ N and from 46 to 1 hPa (∼ 21–48 km) for1985–2012. There are two main outcomes: (i) we independentlyidentify and confirm many of the data problems previouslyidentified, but which remain unaccounted for in existingcomposites; (ii) we construct an ozone composite, withuncertainties, that is free from most of these problems – wecall this the BAyeSian Integrated and Consolidated (BASIC)composite. To analyse the new BASIC composite, we usedynamical linear modelling (DLM), which provides a morerobust estimate of long-term changes through Bayesian inferencethan MLR. BASIC and DLM, together, provide astep forward in improving estimates of decadal trends. Ourresults indicate a significant recovery of ozone since 1998 inthe upper stratosphere, of both northern and southern midlatitudes,in all f
  • Journal article
    White B, Gryspeerdt E, Stier P, Morrison H, Thompson Get al., 2017,

    Uncertainty from the choice of microphysics scheme in convection-permitting models significantly exceeds aerosol effects

    , Atmospheric Chemistry and Physics Discussions, Vol: 17, Pages: 12145-12175, ISSN: 1680-7367

    This study investigates the hydrometeor development and response to cloud droplet number concentration (CDNC) perturbations in convection-permitting model configurations. We present results from a real-data simulation of deep convection in the Congo basin, an idealised supercell case, and a warm-rain large-eddy simulation (LES). In each case we compare two frequently used double-moment bulk microphysics schemes and investigate the response to CDNC perturbations. In the Congo basin simulations both microphysics schemes have large positive biases in surface precipitation, frequency of high radar reflectivities and frequency of cold cloud compared to observations. In all cases, differences in the simulated cloud morphology and precipitation are found to be significantly greater between the microphysics schemes than due to CDNC perturbations within each scheme. Further, we show that the response of the hydrometeors to CDNC perturbations strongly differs not just between microphysics schemes but also between different cases of convection. Sensitivity tests show that the representation of autoconversion is the dominant factor that drives differences in rain production between the microphysics schemes in the idealised precipitating shallow cumulus case and in a sub-region of the Congo basin simulations dominated by liquid-phase processes. In this region, rain mass is also shown to be relatively insensitive to the radiative effects of an overlying layer of ice-phase cloud. In the idealised supercell case, thermodynamic impacts on the storm system using different microphysics parameterisations can equal those due to aerosol effects. These results highlight the large uncertainty in cloud and precipitation responses to aerosol in convection-permitting simulations and have important implications not just for modelling studies of aerosol-convection interaction. These results indicate the continuing need for tighter observational constraints of cloud processes and response to aer
  • Journal article
    Lacombe C, Alexandrova O, Matteini L, 2017,

    Anisotropies of the Magnetic Field Fluctuations at Kinetic Scales in the Solar Wind: Cluster Observations

    , ASTROPHYSICAL JOURNAL, Vol: 848, ISSN: 0004-637X

    We present the first statistical study of the anisotropy of the magnetic field turbulence in the solar wind between 1 and 200 Hz, i.e., from proton to sub-electron scales. We consider 93 ten-minute intervals of the Cluster/STAFF measurements. We find that the fluctuations $\delta {B}_{\perp }^{2}$ are not gyrotropic at a given frequency f, a property already observed at larger scales ($\parallel /\perp $ means parallel/perpendicular to the average magnetic ${{\boldsymbol{B}}}_{0}$). This non-gyrotropy gives indications of the angular distribution of the wave vectors ${\boldsymbol{k}}$: at $f\lt $ 10 Hz, we find that ${k}_{\perp }\gg {k}_{\parallel }$, mainly in the fast wind; at $f\,\gt $ 10 Hz, fluctuations with a non-negligible k ∥ are also present. We then consider the anisotropy ratio $\delta {B}_{\parallel }^{2}/\delta {B}_{\perp }^{2}$, which is a measure of the magnetic compressibility of the fluctuations. This ratio, always smaller than 1, increases with f. It reaches a value showing that the fluctuations are more or less isotropic at electron scales, for $f\geqslant 50\,\mathrm{Hz}$. From 1 to 15–20 Hz, there is a strong correlation between the observed compressibility and the one expected for the kinetic Alfvén waves (KAWs), which only depends on the total plasma β. For $f\gt 15\mbox{--}20\,\mathrm{Hz}$, the observed compressibility is larger than expected for KAWs, and it is stronger in the slow wind: this could be an indication of the presence of a slow-ion acoustic mode of fluctuations, which is more compressive and is favored by the larger values of the electron to proton temperature ratio generally observed in the slow wind.
  • Journal article
    Farrugia CJ, Lugaz N, Alm L, Vasquez B, Argall MR, Kucharek H, Matsui H, Torbert RB, Lavraud B, LeContel O, Cohen IJ, Burch JL, Russell CT, Strangeway RJ, Shuster J, Dorelli JC, Eastwood JP, Ergun RE, Fuselier SA, Gershman DJ, Giles BL, Khotyaintsev YV, Lindqvist PA, Marklund GT, Paulson KW, Petrinec SM, Phan TD, Pollock CJet al., 2017,

    MMS Observations of Reconnection at Dayside Magnetopause Crossings During Transitions of the Solar Wind to Sub-Alfvénic Flow

    , Journal of Geophysical Research: Space Physics, Vol: 122, Pages: 9934-9951, ISSN: 2169-9380

    We present MMS observations during two dayside magnetopause crossings under hithertounexamined conditions: (i) when the bow shock is weakening and the solar wind transitioning tosub-Alfvénic flow and (ii) when it is reforming. Interplanetary conditions consist of a magnetic cloud with (i)a strongB(∼20 nT) pointing south and (ii) a density profile with episodic decreases to values of∼0.3 cm−3followed by moderate recovery. During the crossings the magnetosheath magnetic field is stronger thanthe magnetosphere field by a factor of∼2.2. As a result, during the outbound crossing through the iondiffusion region, MMS observed an inversion of the relative positions of the X and stagnation (S) lines fromthat typically the case: the S line was closer to the magnetosheath side. The S line appears in the form of aslow expansion fan near which most of the energy dissipation is taking place. While in the magnetospherebetween the crossings, MMS observed strong field and flow perturbations, which we argue to be due tokinetic Alfvén waves. During the reconnection interval, whistler mode waves generated by an electrontemperature anisotropy (Te⟂>Te∥) were observed. Another aim of the paper is to distinguish bowshock-induced field and flow perturbations from reconnection-related signatures. The high-resolutionMMS data together with 2-D hybrid simulations of bow shock dynamics helped us to distinguish betweenthe two sources. We show examples of bow shock-related effects (such as heating) and reconnectioneffects such as accelerated flows satisfying the Walén relation.
  • Journal article
    Gingell IL, Schwartz SJ, Burgess D, Johlander A, Russell CT, Burch JL, Ergun RE, Fuselier S, Gershman DJ, Giles BL, Goodrich KA, Khotyaintsev YV, Lavraud B, Lindqvist P-A, Strangeway RJ, Trattner K, Torbert RB, Wei H, Wilder Fet al., 2017,

    MMS observations and hybrid simulations of surface ripples at a marginally quasi-parallel shock

    , Journal of Geophysical Research: Space Physics, Vol: 122, Pages: 11003-11017, ISSN: 2169-9380

    Simulations and observations of collisionless shocks have shown that deviations of the nominal local shock normal orientation, i.e. surface waves or ripples, are expected to propagate in the ramp and overshoot of quasi-perpendicular shocks. Here, we identify signatures of a surface ripple propagating during a crossing of Earth's marginally quasi-parallel (θBn∼45∘) or quasi-parallel bow shock shock on 2015-11-27 06:01:44 UTC by the Magnetospheric Multiscale (MMS) mission, and determine the ripple's properties using multi-spacecraft methods. Using two-dimensional hybrid simulations, we confirm that surface ripples are a feature of marginally quasi-parallel and quasi-parallel shocks under the observed solar wind conditions. In addition, since these marginally quasi-parallel and quasi-parallel shocks are expected to undergo a cyclic reformation of the shock front, we discuss the impact of multiple sources of non-stationarity on shock structure. Importantly, ripples are shown to be transient phenomena, developing faster than an ion gyroperiod and only during the period of the reformation cycle when a newly developed shock ramp is unaffected by turbulence in the foot. We conclude that the change in properties of the ripple observed by MMS is consistent with the reformation of the shock front over a timescale of an ion gyro-period.
  • Journal article
    Morimoto S, Fujita R, Aoki S, Goto D, Nakazawa Tet al., 2017,

    Long-term variations of the mole fraction and carbon isotope ratio of atmospheric methane observed at Ny-Ålesund, Svalbard from 1996 to 2013

    , Tellus B: Chemical and Physical Meteorology, Vol: 69, Pages: 1380497-1380497
  • Journal article
    Westphal A, Riedl KM, Cooperstone JL, Kamat S, Balasubramaniam VM, Schwartz SJ, Boehm Vet al., 2017,

    High-Pressure Processing of Broccoli Sprouts: Influence on Bioactivation of Glucosinolates to Isothiocyanates

    , JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY, Vol: 65, Pages: 8578-8585, ISSN: 0021-8561
  • Journal article
    Southwood D, Brekke P, 2017,

    Norway's most celebrated scientist

    , Astronomy and Geophysics, Vol: 58, Pages: 5.28-5.31, ISSN: 1366-8781
  • Journal article
    Plaschke F, Karlsson T, Hietala H, Archer M, Voeroes Z, Nakamura R, Magnes W, Baumjohann W, Torbert RB, Russell CT, Giles BLet al., 2017,

    Magnetosheath high-speed jets: internal structure and interaction with ambient plasma

    , Journal of Geophysical Research: Space Physics, Vol: 122, Pages: 10157-10175, ISSN: 2169-9380

    For the first time, we have studied the rich internal structure of a magnetosheath high‐speed jet. Measurements by the Magnetospheric Multiscale (MMS) spacecraft reveal large‐amplitude density, temperature, and magnetic field variations inside the jet. The propagation velocity and normal direction of planar magnetic field structures (i.e., current sheets and waves) are investigated via four‐spacecraft timing. We find structures to mainly convect with the jet plasma. There are indications of the presence of a tangential discontinuity. At other times, there are small cross‐structure flows. Where this is the case, current sheets and waves overtake the plasma in the jet's core region; ahead and behind that core region, along the jet's path, current sheets are overtaken by the plasma; that is, they move in opposite direction to the jet in the plasma rest frame. Jet structures are found to be mainly thermal and magnetic pressure balance structures, notwithstanding that the dynamic pressure dominates by far. Although the jet is supermagnetosonic in the Earth's frame of reference, it is submagnetosonic with respect to the plasma ahead. Consequently, we find no fast shock. Instead, we find some evidence for (a series of) jets pushing ambient plasma out of their way, thereby stirring the magnetosheath and causing anomalous sunward flows in the subsolar magnetosheath. Furthermore, we find that jets modify the magnetic field in the magnetosheath, aligning it with their propagation direction.
  • Journal article
    Messing L, Brindley H, 2017,

    Psychologically led multidisciplinary treatment streams within adult mental health teams

    , Clinical Psychology Forum, Pages: 18-25, ISSN: 1747-5732
  • Journal article
    Desai RT, Cowee MM, Wei H, Fu X, Gary SP, Volwerk M, Coates AJet al., 2017,

    Hybrid simulations of positively and negatively charged pickup Ions and cyclotron wave generation at Europa

    , Journal of Geophysical Research: Space Physics, Vol: 122, Pages: 10408-10420, ISSN: 2169-9380

    In the vicinity of Europa, Galileo observed bursty Alfvén-cyclotron wave power at the gyrofrequencies of a number of species including K+, O urn:x-wiley:jgra:media:jgra53834:jgra53834-math-0001, Na+, and Cl+, indicating the localized pickup of these species. Additional evidence for the presence of chlorine was the occurrence of both left-hand (LH) and right-hand (RH) polarized transverse wave power near the Cl+ gyrofrequency, thought to be due to the pickup of both Cl+ and the easily formed chlorine anion, Cl−. To test this hypothesis, we use one-dimensional hybrid (kinetic ion, massless fluid electron) simulations for both positive and negative pickup ions and self-consistently reproduce the growth of both LH and RH Alfvén-cyclotron waves in agreement with linear theory. We show how the simultaneous generation of LH and RH waves can result in nongyrotropic ion distributions and increased wave amplitudes, and how even trace quantities of negative pickup ions are able to generate an observable RH signal. Through comparing simulated and observed wave amplitudes, we are able to place the first constraints on the densities of Chlorine pickup ions in localized regions at Europa.
  • Journal article
    Balogh A, Falanga M, 2017,

    Foreword: A Conclusion to the ISSI Series on Astrophysical Magnetic Fields

    , SPACE SCIENCE REVIEWS, Vol: 212, Pages: 519-521, ISSN: 0038-6308
  • Journal article
    Plaschke F, Goetz C, Volwerk M, Richter I, Fruehauff D, Narita Y, Glassmeier K-H, Dougherty MKet al., 2017,

    Fluxgate magnetometer offset vector determination by the 3D mirror mode method

    , Monthly Notices of the Royal Astronomical Society, Vol: 469, Pages: S675-S684, ISSN: 0035-8711

    Fluxgate magnetometers on-board spacecraft need to be regularly calibrated in flight. In low fields, the most important calibration parameters are the three offset vector components, which represent the magnetometer measurements in vanishing ambient magnetic fields. In case of three-axis stabilized spacecraft, a few methods exist to determine offsets: (i) by analysis of Alfvénic fluctuations present in the pristine interplanetary magnetic field, (ii) by rolling the spacecraft around at least two axes, (iii) by cross-calibration against measurements from electron drift instruments or absolute magnetometers, and (iv) by taking measurements in regions of well-known magnetic fields, e.g. cometary diamagnetic cavities. In this paper, we introduce a fifth option, the 3-dimensional (3D) mirror mode method, by which 3D offset vectors can be determined using magnetic field measurements of highly compressional waves, e.g. mirror modes in the Earth’s magnetosheath. We test the method by applying it to magnetic field data measured by the following: the Time History of Events and Macroscale Interactions during Substorms-C spacecraft in the terrestrial magnetosheath, the Cassini spacecraft in the Jovian magnetosheath and the Rosetta spacecraft in the vicinity of comet 67P/Churyumov–Gerasimenko. The tests reveal that the achievable offset accuracies depend on the ambient magnetic field strength (lower strength meaning higher accuracy), on the length of the underlying data interval (more data meaning higher accuracy) and on the stability of the offset that is to be determined.
  • Journal article
    Keeling RF, Graven HD, Welp LR, Resplandy L, Bi J, Piper SC, Sun Y, Bollenbacher A, Meijer HAJet al., 2017,

    Atmospheric evidence for a global secular increase in carbon isotopic discrimination of land photosynthesis

    , Proceedings of the National Academy of Sciences of the United States of America, Vol: 114, Pages: 10361-10366, ISSN: 0027-8424

    A decrease in the 13C/12C ratio of atmospheric CO2 has been documented by direct observations since 1978 and from ice core measurements since the industrial revolution. This decrease, known as the 13C-Suess effect, is driven primarily by the input of fossil fuel-derived CO2 but is also sensitive to land and ocean carbon cycling and uptake. Using updated records, we show that no plausible combination of sources and sinks of CO2 from fossil fuel, land, and oceans can explain the observed 13C-Suess effect unless an increase has occurred in the 13C/12C isotopic discrimination of land photosynthesis. A trend toward greater discrimination under higher CO2 levels is broadly consistent with tree ring studies over the past century, with field and chamber experiments, and with geological records of C3 plants at times of altered atmospheric CO2, but increasing discrimination has not previously been included in studies of long-term atmospheric 13C/12C measurements. We further show that the inferred discrimination increase of 0.014 ± 0.007‰ ppm−1 is largely explained by photorespiratory and mesophyll effects. This result implies that, at the global scale, land plants have regulated their stomatal conductance so as to allow the CO2 partial pressure within stomatal cavities and their intrinsic water use efficiency to increase in nearly constant proportion to the rise in atmospheric CO2 concentration.
  • Journal article
    Saunois M, Bousquet P, Poulter B, Peregon A, Ciais P, Canadell JG, Dlugokencky EJ, Etiope G, Bastviken D, Houweling S, Janssens-Maenhout G, Tubiello FN, Castaldi S, Jackson RB, Alexe M, Arora VK, Beerling DJ, Bergamaschi P, Blake DR, Brailsford G, Bruhwiler L, Crevoisier C, Crill P, Covey K, Frankenberg C, Gedney N, Hoeglund-Isaksson L, Ishizawa M, Ito A, Joos F, Kim H-S, Kleinen T, Krummel P, Lamarque J-F, Langenfelds R, Locatelli R, Machida T, Maksyutov S, Melton JR, Morino I, Naik V, O'Doherty S, Parmentier F-J, Patra PK, Peng C, Peng S, Peters GP, Pison I, Prinn R, Ramonet M, Riley WJ, Saito M, Santini M, Schroeder R, Simpson IJ, Spahni R, Takizawa A, Thornton BF, Tian H, Tohjima Y, Viovy N, Voulgarakis A, Weiss R, Wilton DJ, Wiltshire A, Worthy D, Wunch D, Xu X, Yoshida Y, Zhang B, Zhang Z, Zhu Qet al., 2017,

    Variability and quasi-decadal changes in the methane budget over the period 2000-2012

    , Atmospheric Chemistry and Physics, Vol: 17, Pages: 11135-11161, ISSN: 1680-7316

    Following the recent Global Carbon Project (GCP) synthesis of the decadal methane (CH4) budget over 2000–2012 (Saunois et al., 2016), we analyse here the same dataset with a focus on quasi-decadal and inter-annual variability in CH4 emissions. The GCP dataset integrates results from top-down studies (exploiting atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up models (including process-based models for estimating land surface emissions and atmospheric chemistry), inventories of anthropogenic emissions, and data-driven approaches. The annual global methane emissions from top-down studies, which by construction match the observed methane growth rate within their uncertainties, all show an increase in total methane emissions over the period 2000–2012, but this increase is not linear over the 13 years. Despite differences between individual studies, the mean emission anomaly of the top-down ensemble shows no significant trend in total methane emissions over the period 2000–2006, during the plateau of atmospheric methane mole fractions, and also over the period 2008–2012, during the renewed atmospheric methane increase. However, the top-down ensemble mean produces an emission shift between 2006 and 2008, leading to 22 [16–32] Tg CH4 yr−1 higher methane emissions over the period 2008–2012 compared to 2002–2006. This emission increase mostly originated from the tropics, with a smaller contribution from mid-latitudes and no significant change from boreal regions. The regional contributions remain uncertain in top-down studies. Tropical South America and South and East Asia seem to contribute the most to the emission increase in the tropics. However, these two regions have only limited atmospheric measurements and remain therefore poorly constrained. The sectorial partitioning of this emission increase between the periods 2002–2006 and 2008–2012 differs from one atmospheric in
  • Journal article
    Mendillo M, Narvaez C, Vogt MF, Mayyasi M, Forbes J, Galand M, Thiemann E, Benna M, Eparvier F, Chamberlin P, Mahaffy P, Andersson Let al., 2017,

    Sources of ionospheric variability at Mars

    , Journal of Geophysical Research: Space Physics, Vol: 122, Pages: 9670-9684, ISSN: 2169-9380

    During the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission's deep-dip #2 campaign of 17–22 April 2015, spacecraft instruments observed all of the physical parameters needed to assess the photo-chemical-equilibrium (PCE) explanation for ionospheric variability at a fixed altitude (135 km) near the peak of the Martian ionosphere. MAVEN measurements of electron density, electron temperature, neutral CO2 density, and solar irradiance were collected during 28 orbits. When inserted into the PCE equation, the measurements of varying PCE drivers correlated with the observed electron density variations to within instrumental uncertainty levels. The dominant source of this positive correlation was the variability of CO2 densities associated with the longitudinal wave-2 component of nonmigrating tides in the Martian thermosphere.
  • Journal article
    Nakamura R, Nagai T, Birn J, Sergeev VA, Le Contel O, Varsani A, Baumjohann W, Nakamura T, Apatenkov S, Artemyev A, Ergun RE, Fuselier SA, Gershman DJ, Giles BJ, Khotyaintsev YV, Lindqvist P-A, Magnes W, Mauk B, Russell CT, Singer HJ, Stawarz J, Strangeway RJ, Anderson B, Bromund KR, Fischer D, Kepko L, Le G, Plaschke F, Slavin JA, Cohen I, Jaynes A, Turner DLet al., 2017,

    Near-Earth plasma sheet boundary dynamics during substorm dipolarization

    , Earth, Planets and Space, Vol: 69, ISSN: 1880-5981

    We report on the large-scale evolution of dipolarization in the near-Earth plasma sheet during an intense (AL ~ −1000 nT) substorm on August 10, 2016, when multiple spacecraft at radial distances between 4 and 15 R E were present in the night-side magnetosphere. This global dipolarization consisted of multiple short-timescale (a couple of minutes) B z disturbances detected by spacecraft distributed over 9 MLT, consistent with the large-scale substorm current wedge observed by ground-based magnetometers. The four spacecraft of the Magnetospheric Multiscale were located in the southern hemisphere plasma sheet and observed fast flow disturbances associated with this dipolarization. The high-time-resolution measurements from MMS enable us to detect the rapid motion of the field structures and flow disturbances separately. A distinct pattern of the flow and field disturbance near the plasma boundaries was found. We suggest that a vortex motion created around the localized flows resulted in another field-aligned current system at the off-equatorial side of the BBF-associated R1/R2 systems, as was predicted by the MHD simulation of a localized reconnection jet. The observations by GOES and Geotail, which were located in the opposite hemisphere and local time, support this view. We demonstrate that the processes of both Earthward flow braking and of accumulated magnetic flux evolving tailward also control the dynamics in the boundary region of the near-Earth plasma sheet.
  • Journal article
    Yao ZH, Coates AJ, Ray LC, Rae IJ, Grodent D, Jones GH, Dougherty MK, Owen CJ, Guo RL, Dunn WR, Radioti A, Pu ZY, Lewis GR, Waite JH, Gerard J-Cet al., 2017,

    Corotating Magnetic Reconnection Site in Saturn's Magnetosphere

    , ASTROPHYSICAL JOURNAL LETTERS, Vol: 846, ISSN: 2041-8205

    Using measurements from theCassinispacecraft in Saturn’s magnetosphere, we propose a 3D physical picture of acorotating reconnection site, which can only be driven by an internally generated source. Our results demonstratethat the corotating magnetic reconnection can drive an expansion of the current sheet in Saturn’s magnetosphereand, consequently, can produce Fermi acceleration of electrons. This reconnection site lasted for longer than one ofSaturn’s rotation period. The long-lasting and corotating natures of the magnetic reconnection site at Saturnsuggest fundamentally different roles of magnetic reconnection in driving magnetospheric dynamics(e.g., theauroral precipitation)from the Earth. Our corotating reconnection picture could also potentially shed light on thefast rotating magnetized plasma environments in the solar system and beyond.

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