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Versailles, France

Welsh B.Y.,University of California at Berkeley | Wheatley J.,University of California at Berkeley | Lallement R.,IPSL
Astronomy and Astrophysics | Year: 2012

Aims. We present medium resolution ultraviolet interstellar absorption measurements recorded with the HST-COS and FUSE spectrographs towards two post-AGB stars (K 559 & K 648) located within the M 15 globular cluster (l ∼ 65°, b ∼-27°). By sampling interstellar gas over the 10.4 kpc sight-line towards M 15 we wish to reveal spectral features that are associated with absorption due to the foreground g1 intermediate velocity cloud (IVC), whose distance has previously been constrained to lie between 1.8-3.8 kpc. Methods. Inspection of the UV line profiles recorded towards both stars have revealed measurable IVC absorption at V lsr ∼ +61.5 ± 5 k s -1 in the profiles of the CI, CII, CII*, CIV, NI, NII, OI, OVI, AlII, SiII, SiIII, SiIV, PII, SII, FeII, FeIII and NiII ions. Line-profile fitting to the IVC absorption features has resulted in column density determinations for the low and high ions. The best-fit column density values for the various ions have near identical values along both sight-lines, such that our UV data does not reveal the significant small-scale structure that has been reported previously for the g1 cloud. Results. The observed column density ratios of the CIV, SiIV, OVI and NV IV components are consistent with what may be expected from turbulent mixing layers, shock ionization or halo SNR models, although no one model can predict all of the observed ratios. We derive sub-solar metallicity values of [O/H] =-1.22 ± 0.44 and [N/H] =-1.21 ± 0.38 for the neutral IVC gas, and also the IV components of C, Si, Al, Ni and Fe mainly possess less than solar abundance ratios relative to that of N. A possible origin for the g1 IVC is that of a low metallicity cloud that has been accreted towards our galaxy, has passed through the disk and is now moving away from the galactic plane. © 2012 ESO. Source

Szopa S.,French Climate and Environment Sciences Laboratory | Balkanski Y.,French Climate and Environment Sciences Laboratory | Schulz M.,French Climate and Environment Sciences Laboratory | Schulz M.,Norwegian Meteorological Institute | And 14 more authors.
Climate Dynamics | Year: 2013

Global aerosol and ozone distributions and their associated radiative forcings were simulated between 1850 and 2100 following a recent historical emission dataset and under the representative concentration pathways (RCP) for the future. These simulations were used in an Earth System Model to account for the changes in both radiatively and chemically active compounds, when simulating the climate evolution. The past negative stratospheric ozone trends result in a negative climate forcing culminating at -0. 15 W m-2 in the 1990s. In the meantime, the tropospheric ozone burden increase generates a positive climate forcing peaking at 0. 41 W m-2. The future evolution of ozone strongly depends on the RCP scenario considered. In RCP4. 5 and RCP6. 0, the evolution of both stratospheric and tropospheric ozone generate relatively weak radiative forcing changes until 2060-2070 followed by a relative 30 % decrease in radiative forcing by 2100. In contrast, RCP8. 5 and RCP2. 6 model projections exhibit strongly different ozone radiative forcing trajectories. In the RCP2. 6 scenario, both effects (stratospheric ozone, a negative forcing, and tropospheric ozone, a positive forcing) decline towards 1950s values while they both get stronger in the RCP8. 5 scenario. Over the twentieth century, the evolution of the total aerosol burden is characterized by a strong increase after World War II until the middle of the 1980s followed by a stabilization during the last decade due to the strong decrease in sulfates in OECD countries since the 1970s. The cooling effects reach their maximal values in 1980, with -0. 34 and -0. 28 W m-2 respectively for direct and indirect total radiative forcings. According to the RCP scenarios, the aerosol content, after peaking around 2010, is projected to decline strongly and monotonically during the twenty-first century for the RCP8. 5, 4. 5 and 2. 6 scenarios. While for RCP6. 0 the decline occurs later, after peaking around 2050. As a consequence the relative importance of the total cooling effect of aerosols becomes weaker throughout the twenty-first century compared with the positive forcing of greenhouse gases. Nevertheless, both surface ozone and aerosol content show very different regional features depending on the future scenario considered. Hence, in 2050, surface ozone changes vary between -12 and +12 ppbv over Asia depending on the RCP projection, whereas the regional direct aerosol radiative forcing can locally exceed -3 W m-2. © 2012 The Author(s). Source

Robinson L.F.,University of Bristol | Robinson L.F.,Woods Hole Oceanographic Institution | Adkins J.F.,California Institute of Technology | Frank N.,IPSL | And 4 more authors.
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2014

Deep-sea corals were discovered over a century ago, but it is only over recent years that focused efforts have been made to explore the history of the oceans using the geochemistry of their skeletal remains. They offer a promising archive of past oceanic environments given their global distribution, layered growth patterns, longevity and preservation as well as our ability to date them using radiometric techniques. This paper provides an overview of the current state-of-the-art in terms of geochemical approaches to using deep-sea coral skeletons to explore the history of the ocean. Deep-sea coral skeletons have a wide array of morphologies (e.g. solitary cup corals, branching colonial corals) and materials (calcite, aragonite and proteins). As such their biomineralization strategies are diverse, leading to complex geochemistry within coral skeletons. Notwithstanding these complications, progress has been made on developing methods for reconstructing the oceanographic environment in the past using trace elements and isotopic methods. Promising approaches within certain coral groups include clumped isotopes and Mg/Li for temperature reconstructions, boron isotopes and radiocarbon for carbon cycling, εNd, and radiocarbon for circulation studies and δ15N, P/Ca and Ba/Ca for nutrient tracer studies. Likewise there is now a range of techniques for dating deep-sea corals skeletons (e.g. U-series, radiocarbon), and determining their growth rates (e.g. radiocarbon and 210Pb). Dating studies on historic coral populations in the Atlantic, Southern Ocean and Pacific point to climate and environmental changes being dominant controls on coral populations over millennial and orbital timescales. This paper provides a review of a range of successes and promising approaches. It also highlights areas in which further research would likely provide new insights into biomineralization, palaeoceanography and distribution of past coral populations. © 2013 Elsevier Ltd. Source

Aumont O.,IPSL | Ethe C.,Institute Pierre et Simon Laplace | Tagliabue A.,University of Liverpool | Bopp L.,French Climate and Environment Sciences Laboratory | Gehlen M.,French Climate and Environment Sciences Laboratory
Geoscientific Model Development | Year: 2015

PISCES-v2 (Pelagic Interactions Scheme for Carbon and Ecosystem Studies volume 2) is a biogeochemical model which simulates the lower trophic levels of marine ecosystems (phytoplankton, microzooplankton and mesozooplankton) and the biogeochemical cycles of carbon and of the main nutrients (P, N, Fe, and Si). The model is intended to be used for both regional and global configurations at high or low spatial resolutions as well as for short-term (seasonal, interannual) and long-term (climate change, paleoceanography) analyses. There are 24 prognostic variables (tracers) including two phytoplankton compartments (diatoms and nanophytoplankton), two zooplankton size classes (microzooplankton and mesozooplankton) and a description of the carbonate chemistry. Formulations in PISCES-v2 are based on a mixed Monod-quota formalism. On the one hand, stoichiometry of C / N / P is fixed and growth rate of phytoplankton is limited by the external availability in N, P and Si. On the other hand, the iron and silicon quotas are variable and the growth rate of phytoplankton is limited by the internal availability in Fe. Various parameterizations can be activated in PISCES-v2, setting, for instance, the complexity of iron chemistry or the description of particulate organic materials. So far, PISCES-v2 has been coupled to the Nucleus for European Modelling of the Ocean (NEMO) and Regional Ocean Modeling System (ROMS) systems. A full description of PISCES-v2 and of its optional functionalities is provided here. The results of a quasi-steady-state simulation are presented and evaluated against diverse observational and satellite-derived data. Finally, some of the new functionalities of PISCES-v2 are tested in a series of sensitivity experiments. © Author(s) 2015. Source

Guilyardi E.,University of Reading | Lawrence B.,University of Reading | Callaghan S.,Rutherford Appleton Laboratory | Deluca C.,National Oceanic and Atmospheric Administration | And 5 more authors.
Bulletin of the American Meteorological Society | Year: 2013

A project named the Coupled Model Intercomparison Project (CMIP5), that seeks to collect better documentation of climate models and their simulations is reviewed. The (CMIP5), organized by the Working Group on Coupled Modelling (WGCM) on behalf of WMO's World Climate Research Program (WCRP), will generate more than a million individual datasets and several petabytes of data. In early planning stages of CMIP5, the climate modeling community was committed to collecting a comprehensive and standardized set of metadata for the climate model simulations. The various types of metadata of interest were then organized into a new conceptual model, called the CIM (Common Information Model). This conceptual model was applied to the specific needs of CMIP5, and a metadata entry tool was developed to collect the information. Data portals can harvest the information contained in the resulting machine-readable files and render it in a form more usable to humans. Source

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