Publications (8)0 Total impact
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Article: Optical Turbulence above the Internal Antarctic Plateau
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ABSTRACT: The internal antarctic plateau revealed in the last years to be a site with interesting potentialities for the astronomical applications due to the extreme dryness and low temperatures, the typical high altitude of the plateau, the weak level of turbulence in the free atmosphere down to a just few tens of meters from the ground and the thin optical turbulence layer developed at the ground. The main goal of a site testing assessment above the internal antarctic plateau is to characterize the site (optical turbulence and classical meteorological parameters) and to quantify which is the gain we might obtain with respect to equivalent astronomical observations done above mid-latitude sites to support plans for future astronomical facilities. Our group is involved, since a few years, in studies related to the assessment of this site for astronomical applications that include the characterization of the meteorological parameters and optical turbulence provided by general circulation models as well as mesoscale atmospherical models and the quantification of the performances of Adaptive Optics (AO) systems. In this talk I will draw the status of art of this site assessment putting our studies in the context of the wide international site testing activity that has been done in Antarctica. I will focus on the site assessment relevant for astronomical applications to be done in the visible up to the near infrared ranges, i.e. those ranges for which the optical turbulence represents a perturbing element for the quality of the images and the AO techniques an efficient tool to correct these wavefront perturbations. Comment: 3 figures01/2010; -
Article: Modelling LAI at a regional scale with ISBA-A-gs: comparison with satellite-derived LAI over southwestern France
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ABSTRACT: A CO2-responsive land surface model (the ISBA-A-gs model of Météo-France) is used to simulate photosynthesis and Leaf Area Index (LAI) in southwestern France for a 3-year period (2001–2003). A domain of about 170 000 km2 is covered at a spatial resolution of 8 km. The capability of ISBA-A-gs to reproduce the seasonal and the inter-annual variability of LAI at a regional scale, is assessed with two satellite-derived LAI products. One originates from the CYCLOPES programme using SPOT/VEGETATION data, and the second is based on MODIS data. The comparison reveals discrepancies between the two satellite LAI estimates and between satellite and simulated LAI values, both in their intensity and in the timing of the leaf onset. The model simulates higher LAI values for the C3 crops and coniferous trees than the satellite observations, which may be due to a saturation effect within the satellite signal. The simulated leaf onset presents a significant delay for mountainous grasslands. In-situ observations at a mid-altitude grassland site show that the generic temperature response of photosynthesis used in the model is not appropriate for plants adapted to the cold climatic conditions of the mountainous areas. This study demonstrates the potential of LAI remote sensing products for identifying and locating models' shortcomings at a regional scale.Biogeosciences Discussions. 01/2009; -
Article: Modelling LAI at a regional scale with ISBA-A-gs: comparison with satellite-derived LAI over southwestern France
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ABSTRACT: A CO2-responsive land surface model (the ISBA-A-gs model of Météo-France) is used to simulate photosynthesis and Leaf Area Index (LAI) in southwestern France for a 3-year period (2001–2003). A domain of about 170 000 km2 is covered at a spatial resolution of 8 km. The capability of ISBA-A-gs to reproduce the seasonal and the interannual variability of LAI at a regional scale, is assessed with satellite-derived LAI products. One originates from the CYCLOPES programme using SPOT/VEGETATION data, and two products are based on MODIS data. The comparison reveals discrepancies between the satellite LAI estimates and between satellite and simulated LAI values, both in their intensity and in the timing of the leaf onset. The model simulates higher LAI values for the C3 crops than the satellite observations, which may be due to a saturation effect within the satellite signal or to uncertainties in model parameters. The simulated leaf onset presents a significant delay for C3 crops and mountainous grasslands. In-situ observations at a mid-altitude grassland site show that the generic temperature response of photosynthesis used in the model is not appropriate for plants adapted to the cold climatic conditions of the mountainous areas. This study demonstrates the potential of LAI remote sensing products for identifying and locating models' shortcomings at a regional scale.Biogeosciences. 01/2009; -
Article: Analysis of Near-Surface Atmospheric Variables: Validation of the SAFRAN Analysis over France
Journal of Applied Meteorology and Climatology. 01/2008; 47:92. -
Article: Hydrometeorological modeling of the Seine basin using the SAFRAN-ISBA-MODCOU system
J. Geophys. Res. 01/2004; 109:14105. -
Article: Hydro-meteorological modelling of the Rhone basin: general presentation and objectives
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ABSTRACT: The paper presents the French national effort undertaken these 5 last years in order to build a hydrological modelisation of the Rhone catchment, coupling the surface and the atmosphere at regional scale. The modelling strategy is based on the coupling of the operational surface model (the ISBA SVAT scheme), the snow model (CROCUS) of Meteo-France and the distributed hydrological model MODCOU developed at Centre d'Informatique G�ologique de l'Ecole Nationale Sup�rieure des Mines de Paris (CIG/ENSMP). As a first step, the coupled model (called in the following CIRSE) uses prescribed atmospheric forcing deduced from meteorological analysis. Several high resolution databases on a fourteen-year period have been constituted. The first part of the article presents the meteorological forcing database, the discharges database and the soil and vegetation maps. Then, the first results of CIRSE model and its validation on the riverflows are shown. As the coupled model was proved to be able to simulate present hydrology characteristics, it was finally used to conduct a preliminary climate change impact study. The impact of surface air temperature and precipitation variations on the hydrological cycle in a doubling CO2 scenario simulated by the Meteo-France climate General Circulation Model (GCM) are shown.Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere. 01/2001; 26:443--453. -
Article: Reconstitution par arbres de régression du rayonnement visible descendant horaire sur la France continentale, à partir de données in situ et de simulations : Spatialisation et vérification sur des données indépendantes
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ABSTRACT: La nécessité de disposer sur toute la France de séries horaires de rayonnement visible descendant a mené à une reconstitution en deux étapes, à partir de paramètres facilement disponibles : · Une reconstitution en des points où sont disponibles la durée d'insolation, éventuellement des résultats de simulations Safran et des observations de nature et d'étendue des couches nuageuses. La méthode de reconstitution employée est basée sur des moyennes d'ensembles d'arbres de régression. Cette méthode permet de prendre en compte les non linéarités entre les divers intrants météorologiques. Elle est comparée avec d'autres ajustements non-linéaires. Les critères de choix entre les divers algorithmes statistiques sont : la qualité des résultats, la rapidité des apprentissages et la facilité des maintenances logicielles. On n'a pas rencontré de contradiction entre ces 3 critères. Des liaisons sont d'abord établies entre le rayonnement horaire et les autres paramètres météorologiques sur toutes les stations disposant de l'intégralité des données nécessaires. Elles sont d'abord testées par des méthodes de cross-validation sur ces mêmes stations, puis appliquées en tous les points disposant de mesure simultanées de durée d'insolation et de nébulosité (environ un par département). Ces pseudo-observations supplémentaires viennent compléter le réseau d'observations de rayonnement horaire, dont la répartition spatiale est très irrégulière. · La spatialisation à l'échelle de Safran (maille de 8´8km) est alors effectuée par krigeage ordinaire. La validation de ces traitements a porté sur 11 stations indépendantes, non gérées par Météo-France, et sur une période (2004) n'ayant servi à aucun réglage. -
Article: The SAFRAN-ISBA-MODCOU hydrometeorological model applied over France
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ABSTRACT: The hydrometeorological model SIM consists in a meterological analysis system (SAFRAN), a land surface model (ISBA) and a hydrogeological model (MODCOU). It generates atmospheric forcing at an hourly time step, and it computes water and surface energy budgets, the river ow at more than 900 rivergauging stations, and the level of several aquifers. SIM was extended over all of France in order to have a homogeneous nation-wide monitoring of the water resources: it can therefore be used to forecast flood risk and to monitor drought risk over the entire nation. The hydrometeorologival model was applied over a 10-year period from 1995 to 2005. In this paper the databases used by the SIM model are presented, then the 10-year simulation is assessed by using the observations of daily stream-flow, piezometric head, and snow depth. This assessment shows that SIM is able to reproduce the spatial and temporal variabilities of the water fluxes. The efficiency is above 0.55 (reasonable results) for 66 % of the simulated rivergages, and above 0.65 (rather good results) for 36 % of them. However, the SIM system produces worse results during the driest years, which is more likely due to the fact that only few aquifers are simulated explicitly. The annual evolution of the snow depth is well reproduced, with a square correlation coeficient around 0.9 over the large altitude range in the domain. The stream ow observations were used to estimate the overall error of the simulated latent heat ux, which was estimated to be less than 4 %.
