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Journal articleSaunois M, Bousquet P, Poulter B, et al., 2016,
The global methane budget 2000-2012
, Earth System Science Data, Vol: 8, Pages: 697-751, ISSN: 1866-3516The global methane (CH4) budget is becoming an increasingly important component for managing realistic pathways to mitigate climate change. This relevance, due to a shorter atmospheric lifetime and a stronger warming potential than carbon dioxide, is challenged by the still unexplained changes of atmospheric CH4 over the past decade. Emissions and concentrations of CH4 are continuing to increase, making CH4 the second most important human-induced greenhouse gas after carbon dioxide. Two major difficulties in reducing uncertainties come from the large variety of diffusive CH4 sources that overlap geographically, and from the destruction of CH4 by the very short-lived hydroxyl radical (OH). To address these difficulties, we have established a consortium of multi-disciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate research on the methane cycle, and producing regular (∼ biennial) updates of the global methane budget. This consortium includes atmospheric physicists and chemists, biogeochemists of surface and marine emissions, and socio-economists who study anthropogenic emissions. Following Kirschke et al. (2013), we propose here the first version of a living review paper that integrates results of top-down studies (exploiting atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up models, inventories and data-driven approaches (including process-based models for estimating land surface emissions and atmospheric chemistry, and inventories for anthropogenic emissions, data-driven extrapolations). For the 2003–2012 decade, global methane emissions are estimated by top-down inversions at 558 Tg CH4 yr−1, range 540–568. About 60 % of global emissions are anthropogenic (range 50–65 %). Since 2010, the bottom-up global emission inventories have been closer to methane emissions in the most carbon-intensive Representative Concentrations Pathway (RCP8.5) and higher
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Journal articleFranci L, Landi S, Matteini L, et al., 2016,
Plasma beta dependence of the ion-scale spectral break of solar wind turbulence: high-resolution 2D hybrid simulations
, Astrophysical Journal, Vol: 833, ISSN: 0004-637XWe investigate properties of the ion-scale spectral break of solar wind turbulence by means of two-dimensional high-resolution hybrid particle-in-cell simulations. We impose an initial ambient magnetic field perpendicular to the simulation box and add a spectrum of in-plane, large-scale, magnetic and kinetic fluctuations. We perform a set of simulations with different values of the plasma β, distributed over three orders of magnitude, from 0.01 to 10. In all cases, once turbulence is fully developed, we observe a power-law spectrum of the fluctuating magnetic field on large scales (in the inertial range) with a spectral index close to −5/3, while in the sub-ion range we observe another power-law spectrum with a spectral index systematically varying with β (from around −3.6 for small values to around −2.9 for large ones). The two ranges are separated by a spectral break around ion scales. The length scale at which this transition occurs is found to be proportional to the ion inertial length, d i , for β Lt 1 and to the ion gyroradius, ${\rho }_{i}={d}_{i}\sqrt{\beta }$, for β Gt 1, i.e., to the larger between the two scales in both the extreme regimes. For intermediate cases, i.e., β ~ 1, a combination of the two scales is involved. We infer an empiric relation for the dependency of the spectral break on β that provides a good fit over the whole range of values. We compare our results with in situ observations in the solar wind and suggest possible explanations for such a behavior.
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Journal articleFrancis DBK, Flamant C, Chaboureau J-P, et al., 2016,
Dust emission and transport over Iraq associated with the summer Shamal winds
, AEOLIAN RESEARCH, Vol: 24, Pages: 15-31, ISSN: 1875-9637 -
Journal articleGoetz C, Koenders C, Hansen KC, et al., 2016,
Structure and evolution of the diamagnetic cavity at comet 67P/Churyumov-Gerasimenko
, Monthly Notices of the Royal Astronomical Society, Vol: 462, Pages: S459-S467, ISSN: 0035-8711The long duration of the Rosetta mission allows us to study the evolution of the diamagnetic cavity at comet 67P/Churyumov–Gerasimenko in detail. From 2015 April to 2016 February 665 intervals could be identified where Rosetta was located in a zero-magnetic-field region. We study the temporal and spatial distribution of this cavity and its boundary and conclude that the cavity properties depend on the long-term trend of the outgassing rate, but do not respond to transient events at the spacecraft location, such as outbursts or high neutral densities. Using an empirical model of the outgassing rate, we find a functional relationship between the outgassing rate and the distance of the cavity to the nucleus. There is also no indication that this unexpectedly large distance is related to unusual solar wind conditions. Because the deduced shape of the cavity boundary is roughly elliptical on small scales and the distances of the boundary from the nucleus are much larger than expected we conclude that the events observed by Rosetta are due to a moving instability of the cavity boundary itself.
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Journal articleFox NJ, Velli MC, Bale SD, et al., 2016,
The Solar Probe Plus Mission: Humanity's First Visit to Our Star
, SPACE SCIENCE REVIEWS, Vol: 204, Pages: 7-48, ISSN: 0038-6308- Author Web Link
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- Citations: 1051
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Journal articleKasper JC, Abiad R, Austin G, et al., 2016,
Solar Wind Electrons Alphas and Protons (SWEAP) Investigation: Design of the Solar Wind and Coronal Plasma Instrument Suite for Solar Probe Plus
, SPACE SCIENCE REVIEWS, Vol: 204, Pages: 131-186, ISSN: 0038-6308- Author Web Link
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- Citations: 562
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Journal articleMcComas DJ, Alexander N, Angold N, et al., 2016,
Integrated Science Investigation of the Sun (ISIS): Design of the Energetic Particle Investigation
, SPACE SCIENCE REVIEWS, Vol: 204, Pages: 187-256, ISSN: 0038-6308- Author Web Link
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- Citations: 187
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Journal articleStawarz JE, Eriksson S, Wilder FD, et al., 2016,
Observations of turbulence in a Kelvin-Helmholtz event on September 8, 2015 by the Magnetospheric Multiscale Mission
, Journal of Geophysical Research: Space Physics, Vol: 121, Pages: 11021-11034, ISSN: 2169-9380Spatial and high-time-resolution properties of the velocities,magnetic eld, and 3D electric eld within plasma turbulence are examined observationally using data from the Magnetospheric Multiscale Mission. Observations from a Kelvin-Helmholtz instability (KHI) on the Earth's magnetopause are examined, which both provides a series of repeatable intervals to analyze, giving better statistics, and provides a rst look at the properties of turbulence in the KHI. For the rst time direct observations of both the high-frequency ion and electron velocity spectra are examined, showing differing ion and electron behavior at kinetic scales. Temporal spectra ex-hibit power law behavior with changes in slope near the ion gyrofrequency and lower-hybrid frequency. The work provides the rst observational evi-dence for turbulent intermittency and anisotropy consistent with quasi-two-dimensional turbulence in association with the KHI. The behavior of kinetic scale intermittency is found to have di erences from previous studies of solar wind turbulence, leading to novel insights on the turbulent dynamics inthe KHI.
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Journal articleO'Shea SJ, Choularton TW, Lloyd G, et al., 2016,
Airborne observations of the microphysical structure of two contrasting cirrus clouds
, Journal of Geophysical Research: Atmospheres, Vol: 121, Pages: 13510-13536, ISSN: 2169-8996We present detailed airborne in situ measurements of cloud microphysics in two midlatitude cirrus clouds, collected as part of the Cirrus Coupled Cloud-Radiation Experiment. A new habit recognition algorithm for sorting cloud particle images using a neural network is introduced. Both flights observed clouds that were related to frontal systems, but one was actively developing while the other dissipated as it was sampled. The two clouds showed distinct differences in particle number, habit, and size. However, a number of common features were observed in the 2-D stereo data set, including a distinct bimodal size distribution within the higher-temperature regions of the clouds. This may result from a combination of local heterogeneous nucleation and large particles sedimenting from aloft. Both clouds had small ice crystals (<100 µm) present at all levels However, this small ice mode is not present in observations from a holographic probe. This raises the possibility that the small ice observed by optical array probes may at least be in part an instrument artifact due to the counting of out-of-focus large particles as small ice. The concentrations of ice crystals were a factor ~10 higher in the actively growing cloud with the stronger updrafts, with a mean concentration of 261 L−1 compared to 29 L−1 in the decaying case. Particles larger than 700 µm were largely absent from the decaying cirrus case. A comparison with ice-nucleating particle parameterizations suggests that for the developing case the ice concentrations at the lowest temperatures are best explained by homogenous nucleation.
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Journal articleGaland M, Héritier KL, Odelstad E, et al., 2016,
Ionospheric plasma of comet 67P probed by Rosetta at 3 AU from the Sun
, Monthly Notices of the Royal Astronomical Society, Vol: 462, Pages: S331-S351, ISSN: 1365-2966We propose to identify the main sources of ionization of the plasma in the coma of comet 67P/Churyumov–Gerasimenko at different locations in the coma and to quantify their relative importance, for the first time, for close cometocentric distances (<20 km) and large heliocentric distances (>3 au). The ionospheric model proposed is used as an organizing element of a multi-instrument data set from the Rosetta Plasma Consortium (RPC) plasma and particle sensors, from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis and from the Microwave Instrument on the Rosetta Orbiter, all on board the ESA/Rosetta spacecraft. The calculated ionospheric density driven by Rosetta observations is compared to the RPC-Langmuir Probe and RPC-Mutual Impedance Probe electron density. The main cometary plasma sources identified are photoionization of solar extreme ultraviolet (EUV) radiation and energetic electron-impact ionization. Over the northern, summer hemisphere, the solar EUV radiation is found to drive the electron density – with occasional periods when energetic electrons are also significant. Over the southern, winter hemisphere, photoionization alone cannot explain the observed electron density, which reaches sometimes higher values than over the summer hemisphere; electron-impact ionization has to be taken into account. The bulk of the electron population is warm with temperature of the order of 7–10 eV. For increased neutral densities, we show evidence of partial energy degradation of the hot electron energy tail and cooling of the full electron population
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Journal articleJeong S, Newman S, Zhang J, et al., 2016,
Estimating methane emissions in California's urban and rural regions using multitower observations
, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, Vol: 121, Pages: 13031-13049, ISSN: 2169-897X -
Journal articleThomas RT, Prentice IC, Graven H, et al., 2016,
Increased light-use efficiency in northern terrestrial ecosystems indicated by CO2 and greening observations
, Geophysical Research Letters, Vol: 43, Pages: 11339-11349, ISSN: 1944-8007Observations show an increasing amplitude in the seasonal cycle of CO2 (ASC) north of 45°N of 56 ± 9.8% over the last 50 years and an increase in vegetation greenness of 7.5–15% in high northern latitudes since the 1980s. However, the causes of these changes remain uncertain. Historical simulations from terrestrial biosphere models in the Multiscale Synthesis and Terrestrial Model Intercomparison Project are compared to the ASC and greenness observations, using the TM3 atmospheric transport model to translate surface fluxes into CO2 concentrations. We find that the modeled change in ASC is too small but the mean greening trend is generally captured. Modeled increases in greenness are primarily driven by warming, whereas ASC changes are primarily driven by increasing CO2. We suggest that increases in ecosystem-scale light use efficiency (LUE) have contributed to the observed ASC increase but are underestimated by current models. We highlight potential mechanisms that could increase modeled LUE.
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Journal articleGraven HD, 2016,
The carbon cycle in a changing climate
, Physics Today, Vol: 69, Pages: 48-54, ISSN: 0031-9228 -
Journal articleMistry R, Eastwood JP, Haggerty CC, et al., 2016,
Observations of Hall reconnection physics far downstream of the X-line
, Physical Review Letters, Vol: 117, ISSN: 1079-7114Observations made using the Wind spacecraft of Hall magnetic fields in solar wind reconnection exhausts are presented. These observations are consistent with the generation of Hall fields by a narrow ion inertial scale current layer near the separatrix, which is confirmed with an appropriately scaled particle-in-cell simulation that shows excellent agreement with observations. The Hall fields are observed thousands of ion inertial lengths downstream from the reconnection X line, indicating that narrow regions of kinetic dynamics can persist extremely far downstream.
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Journal articleWang S, Toumi R, 2016,
On the relationship between hurricane cost and the integrated wind profile
, Environmental Research Letters, Vol: 11, ISSN: 1748-9326It is challenging to identify metrics that best capture hurricane destructive potential and costs. Although it has been found that the sea surface temperature and vertical wind shear can both make considerable changes to the hurricane destructive potential metrics, it is still unknown which plays a more important role. Here we present a new method to reconstruct the historical wind structure of hurricanes that allows us, for the first time, to calculate the correlation of damage with integrated power dissipation and integrated kinetic energy of all hurricanes at landfall since 1988. We find that those metrics, which include the horizontal wind structure, rather than just maximum intensity, are much better correlated with the hurricane cost. The vertical wind shear over the main development region of hurricanes plays a more dominant role than the sea surface temperature in controlling these metrics and therefore also ultimately the cost of hurricanes.
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Journal articleWang S, Toumi R, 2016,
On the relationship between hurricane cost and the integrated wind profile
, Environmental Research Letters, Vol: 11, ISSN: 1748-9326It is challenging to identify metrics that best capture hurricane destructive potential and costs. Although it has been found that the sea surface temperature and vertical wind shear can both make considerable changes to the hurricane destructive potential metrics, it is still unknown which plays a more important role. Here we present a new method to reconstruct the historical wind structure of hurricanes that allows us, for the first time, to calculate the correlation of damage with integrated power dissipation and integrated kinetic energy of all hurricanes at landfall since 1988. We find that those metrics, which include the horizontal wind structure, rather than just maximum intensity, are much better correlated with the hurricane cost. The vertical wind shear over the main development region of hurricanes plays a more dominant role than the sea surface temperature in controlling these metrics and therefore also ultimately the cost of hurricanes.
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Journal articleProvan G, Cowley SWH, Lamy L, et al., 2016,
Planetary period oscillations in Saturn's magnetosphere: coalescence and reversal of northern and southern periods in late northern spring
, Journal of Geophysical Research: Space Physics, Vol: 121, Pages: 9829-9862, ISSN: 2169-9402We investigate planetary period oscillations (PPOs) in Saturn's magnetosphere using Cassini magnetic field and Saturn kilometric radiation (SKR) data over the interval from late 2012 to the end of 2015, beginning ~3 years after vernal equinox and ending ~1.5 years before northern solstice. Previous studies have shown that the northern and southern PPO periods converged across equinox from southern summer values ~10.8 h for the southern system and ~10.6 h for the northern system and near coalesced ~1 year after equinox, before separating again with the southern period ~10.69 h remaining longer than the northern ~10.64 h. We show that these conditions ended in mid-2013 when the two periods coalesced at ~10.66 h and remained so until mid-2014, increasing together to longer periods ~10.70 h. During coalescence the two systems were locked near magnetic antiphase with SKR modulations in phase, a condition in which the effects of the generating rotating twin vortex flows in the two ionospheres reinforce each other via hemisphere-to-hemisphere coupling. The magnetic-SKR relative phasing indicates the dominance of postdawn SKR sources in both hemispheres, as was generally the case during the study interval. In mid-2014 the two periods separated again, the northern increasing to ~10.78 h by the end of 2015, similar to the southern period during southern summer, while the southern period remained fixed near ~10.70 h, well above the northern period during southern summer. Despite this difference, this behavior resulted in the first enduring reversal of the two periods, northern longer than southern, during the Cassini era.
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Journal articleYates JN, Southwood DJ, Dougherty MK, et al., 2016,
Saturn's quasiperiodic magnetohydrodynamic waves
, Geophysical Research Letters, Vol: 43, Pages: 102-111, ISSN: 1944-8007Quasi-periodic ∼1-hour fluctuations have been recently reported by numerous instruments on-board the Cassini spacecraft. The interpretation of the sources of these fluctuations has remained elusive to date. Here we provide an explanation for the origin of these fluctuations using magnetometer observations. We find that magnetic field fluctuations at high northern latitudes are Alfvénic, with small amplitudes (∼0.4 nT), and are concentrated in wave-packets similar to those observed in Kleindienst et al. [2009]. The wave-packets recur periodically at the northern magnetic oscillation period. We use a magnetospheric box model to provide an interpretation of the wave periods. Our model results suggest that the observed magnetic fluctuations are second harmonic Alfvén waves standing between the northern and southern ionospheres in Saturn’s outer magnetosphere
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Journal articleJohlander A, Schwartz SJ, Vaivads A, et al., 2016,
Rippled Quasiperpendicular Shock Observed by the Magnetospheric Multiscale Spacecraft
, Physical Review Letters, Vol: 117, ISSN: 1079-7114Collisionless shock nonstationarity arising from microscale physics influences shock structure andparticle acceleration mechanisms. Nonstationarity has been difficult to quantify due to the small spatial andtemporal scales. We use the closely spaced (subgyroscale), high-time-resolution measurements from onerapid crossing of Earth’s quasiperpendicular bow shock by the Magnetospheric Multiscale (MMS)spacecraft to compare competing nonstationarity processes. Using MMS’s high-cadence kinetic plasmameasurements, we show that the shock exhibits nonstationarity in the form of ripples.
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Journal articleShebanits O, Wahlund J-E, Edberg NJT, et al., 2016,
Ion and aerosol precursor densities in Titan's ionosphere: A multi-instrument case study
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 121, Pages: 10075-10090, ISSN: 2169-9380 -
Journal articleVaivads A, Retino A, Soucek J, et al., 2016,
Turbulence Heating ObserveR – satellite mission proposal
, Journal of Plasma Physics, Vol: 82, ISSN: 1469-7807The Universe is permeated by hot, turbulent, magnetized plasmas. Turbulent plasma is a major constituent of active galactic nuclei, supernova remnants, the intergalactic and interstellar medium, the solar corona, the solar wind and the Earth’s magnetosphere, just to mention a few examples. Energy dissipation of turbulent fluctuations plays a key role in plasma heating and energization, yet we still do not understand the underlying physical mechanisms involved. THOR is a mission designed to answer the questions of how turbulent plasma is heated and particles accelerated, how the dissipated energy is partitioned and how dissipation operates in different regimes of turbulence. THOR is a single-spacecraft mission with an orbit tuned to maximize data return from regions in near-Earth space – magnetosheath, shock, foreshock and pristine solar wind – featuring different kinds of turbulence. Here we summarize the THOR proposal submitted on 15 January 2015 to the ‘Call for a Medium-size mission opportunity in ESAs Science Programme for a launch in 2025 (M4)’. THOR has been selected by European Space Agency (ESA) for the study phase.
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Journal articleStansby D, Horbury TS, Chen CHK, et al., 2016,
Experimental determination of whistler wave dispersion relation in the solar wind
, Astrophysical Journal Letters, Vol: 829, ISSN: 2041-8213The origins and properties of large-amplitude whistler wavepackets in the solar wind are still unclear. In this Letter, we utilize single spacecraft electric and magnetic field waveform measurements from the ARTEMIS mission to calculate the plasma frame frequency and wavevector of individual wavepackets over multiple intervals. This allows direct comparison of experimental measurements with theoretical dispersion relations to identify the observed waves as whistler waves. The whistlers are right-hand circularly polarized, travel anti-sunward, and are aligned with the background magnetic field. Their dispersion is strongly affected by the local electron parallel beta in agreement with linear theory. The properties measured are consistent with the electron heat flux instability acting in the solar wind to generate these waves.
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Journal articleBarnes WT, Cargill PJ, Bradshaw SJ, 2016,
Inference of heating properties from "hot" non-flaring plasmas in active region cores i. single nanoflares
, Astrophysical Journal, Vol: 829, Pages: 31-31, ISSN: 1538-4357The properties expected of “hot” non-flaring plasmas due to nanoflare heating in active regions areinvestigated using hydrodynamic modeling tools, including a two-fluid development of the EBTELcode. Here we study a single nanoflare and show that while simple models predict an emission measuredistribution extending well above 10 MK that is consistent with cooling by thermal conduction,many other effects are likely to limit the existence and detectability of such plasmas. These include:differential heating between electrons and ions, ionization non-equilibrium and, for short nanoflares,the time taken for the coronal density to increase. The most useful temperature range to look for thisplasma, often called the “smoking gun” of nanoflare heating, lies between 106.6 and 107 K. Signaturesof the actual heating may be detectable in some instances.
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Journal articleParfitt R, Russell JE, Bantges RJ, et al., 2016,
A study of the time evolution of GERB shortwave calibration by comparison with CERES Edition-3A data
, Remote Sensing of Environment, Vol: 186, Pages: 416-427, ISSN: 0034-4257This study examines the evolution of the GERB-2 and GERB-1 Edition 1 shortwave radiance calibration between 2004-2007 and 2007-2012 respectively, through comparison with CERES instrument FM1 Edition 3A SSF instantaneous radiances. Two periods when simultaneous observations from both GERB-2 and GERB-1 were available, January 13th to February 11th 2007 and May 1st to May 10th 2007, are also compared. For these two overlap periods respectively, averaged over all CERES ‘unfiltered-to-filtered radiance ratio’ subsets, the GERB-1/CERES unfiltered radiance ratio is on average found to be 1.6% and 1.9% lower than the associated GERB-2/CERES unfiltered radiance ratio. Over the two longer time series the GERB/CERES unfiltered radiance ratio shows a general decrease with time for both GERB-2 and GERB-1. The rate of decrease varies through time but no significant seasonal dependence is seen. Averaged over all subsets the GERB-2/CERES unfiltered radiance ratio showed a decrease of 1.9% between June 2004 and June 2006. Between June 2007 and June 2012, the corresponding decrease in the GERB-1/CERES unfiltered radiance ratio was 6.5%. The evolution of the GERB/CERES unfiltered radiance ratio for both GERB-2 and GERB-1 shows a strong dependence on the CERES unfiltered-to-filtered radiance ratio, indicating that it is spectrally dependent. Further time-series analysis and theoretical work using simulated spectral radiance curves suggests that for GERB-1 the evolution is consistent with a darkening in the GERB shortwave spectral response function which is most pronounced at the shortest wavelengths. For GERB-2, no single spectral cause can be identified, suggesting that the evolution is likely due to a combination of several different effects.
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Journal articleWatson-Parris D, Schutgens N, Cook N, et al., 2016,
Community Intercomparison Suite (CIS) v1.4.0: a tool for intercomparing models and observations
, Geoscientific Model Development, Vol: 9, Pages: 3093-3110, ISSN: 1991-9603The Community Intercomparison Suite (CIS) is an easy-to-use command-line tool which has been developed to allow the straightforward intercomparison of remote sensing, in situ and model data. While there are a number of tools available for working with climate model data, the large diversity of sources (and formats) of remote sensing and in situ measurements necessitated a novel software solution. Developed by a professional software company, CIS supports a large number of gridded and ungridded data sources "out-of-the-box", including climate model output in NetCDF or the UK Met Office pp file format, CloudSat, CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization), MODIS (MODerate resolution Imaging Spectroradiometer), Cloud and Aerosol CCI (Climate Change Initiative) level 2 satellite data and a number of in situ aircraft and ground station data sets. The open-source architecture also supports user-defined plugins to allow many other sources to be easily added. Many of the key operations required when comparing heterogenous data sets are provided by CIS, including subsetting, aggregating, collocating and plotting the data. Output data are written to CF-compliant NetCDF files to ensure interoperability with other tools and systems. The latest documentation, including a user manual and installation instructions, can be found on our website (http://cistools.net). Here, we describe the need which this tool fulfils, followed by descriptions of its main functionality (as at version 1.4.0) and plugin architecture which make it unique in the field.
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Journal articleWilder FD, Ergun RE, Schwartz SJ, et al., 2016,
Observations of large-amplitude, parallel, electrostatic waves associated with the Kelvin-Helmholtz instability by the magnetospheric multiscale mission
, Geophysical Research Letters, Vol: 43, Pages: 8859-8866, ISSN: 1944-8007On 8 September 2015, the four Magnetospheric Multiscale spacecraft encountered a Kelvin-Helmholtz unstable magnetopause near the dusk flank. The spacecraft observed periodic compressed current sheets, between which the plasma was turbulent. We present observations of large-amplitude (up to 100 mV/m) oscillations in the electric field. Because these oscillations are purely parallel to the background magnetic field, electrostatic, and below the ion plasma frequency, they are likely to be ion acoustic-like waves. These waves are observed in a turbulent plasma where multiple particle populations are intermittently mixed, including cold electrons with energies less than 10 eV. Stability analysis suggests a cold electron component is necessary for wave growth.
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ReportThomas R, Graven H, Hoskins B, et al., 2016,
What is meant by ‘balancing sources and sinks of greenhouse gases’ to limit global temperature rise?
, Grantham Institute Briefing Note, Imperial College London, 3In an effort to limit global temperature rise to well below 2˚C, the COP21 Paris Agreement stipulates that a ‘balance’ between anthropogenic (man-made) sources and sinks of greenhouse gases must be reached by 2050-2100. An overall greenhouse gas ‘balance’ must consider individual gases in terms of how strongly they absorb solar infrared radiation, their concentration in the atmosphere, and their lifetime in the atmosphere.• Long-lived greenhouse gases, including carbon dioxide (CO2), accumulate in the atmosphere and continue to affect the climate for many centuries. To stabilise the concentrations of these long-lived gases, and thereby their effect on the climate, their sources must be progressively reduced towards zero. • For short-lived greenhouse gases that remain in the atmosphere for less than 100 years, including methane, stable or decreasing concentrations could be achieved within decades if emissions were stabilised or decreased. However, these gases currently only contribute about 20% of the total warming from greenhouse gases, so their reduction alone cannot successfully stabilise global temperature.• An overall ‘balance’ of sources and sinks of greenhouse gases could be facilitated by deliberate removal of CO2 from the atmosphere, for example, by combining biomass energy production with carbon capture and storage. Most current greenhouse gas emission scenarios that keep global temperature rise below 2˚C include some deliberate removal of CO2 to compensate for continued emissions of CO2 and other greenhouse gases
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Journal articleTownley-Smith K, Nave G, Pickering JC, et al., 2016,
Hyperfine structure constants for singly ionized manganese (Mn II) using Fourier transform spectroscopy
, Monthly Notices of the Royal Astronomical Society, Vol: 461, Pages: 73-78, ISSN: 0035-8711We expand on the comprehensive study of hyperfine structure (HFS) in Mn II conducted byHolt et al. (1999) by verifying hyperfine magnetic dipole constants (A) for 20 levels previouslymeasured by Holt et al. (1999) and deriving A constants for 47 previously unstudied levels. TheHFS patterns were measured in archival spectra from Fourier transform (FT) spectrometers atImperial College London and the National Institute of Standards and Technology. Analysis ofthe FT spectra was carried out in XGREMLIN. Our A constant for the ground level has a loweruncertainty by a factor of 6 than that of Blackwell-Whitehead et al.
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Journal articleCoustenis A, Atreya S, Castillo J, et al., 2016,
Preface to the special issue of PSS on "Surfaces, atmospheres and magnetospheres of the outer planets and their satellites and ring systems: Part XI"
, PLANETARY AND SPACE SCIENCE, Vol: 130, Pages: 1-2, ISSN: 0032-0633 -
Journal articleGrün E, Agarwal J, Altobelli N, et al., 2016,
The 2016 Feb 19 outburst of comet 67P/CG: an ESA Rosetta multi-instrument study
, Monthly Notices of the Royal Astronomical Society, Vol: 462, Pages: S220-S234, ISSN: 1365-2966On 2016 Feb 19, nine Rosetta instruments serendipitously observed an outburst of gas and dust from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras and spectrometers ranging from UV over visible to microwave wavelengths, in situ gas, dust and plasma instruments, and one dust collector. At 09:40 a dust cloud developed at the edge of an image in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature of the outburst that significantly exceeded the background. The enhancement ranged from 50 per cent of the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus. Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3 and consequently the spacecraft potential changed from ∼−16 V to −20 V during the outburst. A clear sequence of events was observed at the distance of Rosetta (34 km from the nucleus): within 15 min the Star Tracker camera detected fast particles (∼25 m s−1) while 100 μm radius particles were detected by the GIADA dust instrument ∼1 h later at a speed of 6 m s−1. The slowest were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst originated just outside the FOV of the instruments, the source region and the magnitude of the outburst could be determined.
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