VALIDATION OF GOMOS OZONE PROFILES USING NDSC LIDAR : STATISTICAL COMPARISONS

ABSTRACT The lidars deployed in the NDSC framework have been used for the validation of GOMOS onboard ENVISAT. During the commissioning phase around ten coincidences per site have been investigated. No significant bias, larger than ±5 %, has been reported except around 50 km and 20 km where both techniques are known to present some limitations. The estimated errors of both GOMOS and lidar are in good agreement with the standard deviation of the differences between coincidences. At higher latitude, comparisons are not so good because of the measurement conditions of bright limb during this period

L' Alimentation du nourrisson et du jeune enfant (petit manuel à l'usage de l'équipe officinale)

TOURS-BU Sciences Pharmacie (372612104) / SudocSudocFranceF

On the use of Advanced Microwave Sounding Unit‐A and ‐B measurements for studying the monsoon variability over West Africa

International audienceThe advanced microwave sounding unit (AMSU) ‐A and ‐B sensors provide observations of humidity and temperature that are relevant for meteorological and climate studies. The use of these observations in numerical weather prediction models has increased in the past 10 years because of some improvements in data assimilation. However, an appropriate use of AMSU measurements apart from assimilation context is rather difficult and depends for the most part on how successfully the instrumental characteristics are accounted for. In particular, atmosphere humidity and temperature variations can be completely hidden by features because of the effect of the observation zenith angle. In this paper, 8 years of AMSU‐A and ‐B observations have been corrected from the observations zenith angle effect and have been used to study temperature and humidity variations over West Africa. Comparisons have been made between AMSU observations and selected atmospheric fields from European Centre for Medium‐Range Weather Forecasts analyses as well as outgoing longwave radiation estimates. It has been found that observations from AMSU‐A channel 5 can be used to monitor the heat low evolution and that AMSU‐B observations from channels 3 and 5 are well adapted to study the humidity variations in direct link with the African monsoon from intraseasonal to interannual scales

Physical pathways for carbon transfers between the surface mixed layer and the ocean interior

International audienceAlthough they are key components of the surface ocean carbon budget, physical processes inducing carbon fluxes across the mixed‐layer base, i.e., subduction and obduction, have received much less attention than biological processes. Using a global model analysis of the preindustrial ocean, physical carbon fluxes are quantified and compared to the other carbon fluxes in and out of the surface mixed layer, i.e., air‐sea CO2gas exchange and sedimentation of biogenic material. Model‐based carbon obduction and subduction are evaluated against independent data‐based estimates to the extent that was possible. We find that climatological physical fluxes of dissolved inorganic carbon (DIC) are two orders of magnitude larger than the other carbon fluxes and vary over the globe at smaller spatial scale. At temperate latitudes, the subduction of DIC and to a much lesser extent (<10%) the sinking of particles maintain CO2undersaturation, whereas DIC is obducted back to the surface in the tropical band (75%) and Southern Ocean (25%). At the global scale, these two large counter‐balancing fluxes of DIC amount to +275.5 PgC yr−1 for the supply by obduction and −264.5 PgC yr−1 for the removal by subduction which is ∼ 3 to 5 times larger than previous estimates. Moreover, we find that subduction of organic carbon (dissolved and particulate) represents ∼ 20% of the total export of organic carbon: at the global scale, we evaluate that of the 11 PgC yr−1 of organic material lost from the surface every year, 2.1 PgC yr−1 is lost through subduction of organic carbon. Our results emphasize the strong sensitivity of the oceanic carbon cycle to changes in mixed‐layer depth, ocean currents, and wind

Rainfall Intra-Seasonal Variability and Vegetation Growth in the Ferlo Basin (Senegal)

International audienceDuring the monsoon season, the spatiotemporal variability of rainfall impacts the growth of vegetation in the Sahel. This study evaluates this effect for the Ferlo basin in central northern Senegal. Relationships between rainfall, soil moisture (SM), and vegetation are assessed using remote sensing data (TRMM3B42 and RFE 2.0 for rainfall, ESA-CCI.SM for soil moisture and MODIS Leaf Area Index (LAI)). The principal objective was to analyze the response of vegetation growth to water availability during the rainy season using statistical criteria at the scale of homogeneous vegetation-soil zones. The study covers the period from June to September for the years 2000 to 2010. The surface SM is well correlated with both rainfall products. On ferruginous soils, better correlation of intra-seasonal variations and stronger sensitivity of the vegetation to rainfall are found compared to lithosols soils. LAI responds, on average, two to three weeks after a rainfall anomaly. Moreover, dry spells (negative anomalies) of seven days’ length (three days for SM anomaly) significantly affect vegetation growth (maximum LAI within the season). A strong and significant link is also found between total precipitation and the number of dry spells. These datasets proved to be sufficiently reliable to assess the impacts of rainfall variability on vegetation dynamics

Control of shortwave radiation parameterization on tropical climate SST-forced simulation

International audienceSST-forced tropical-channel simulations are used to quantify the control of shortwave (SW) parameterization on the mean tropical climate compared to other major model settings (convection, boundary layer turbulence, vertical and horizontal resolutions), and to pinpoint the physical mechanisms whereby this control manifests. Analyses focus on the spatial distribution and magnitude of the net SW radiation budget at the surface (SWnet_SFC), latent heat fluxes, and rainfall at the annual timescale. The model skill and sensitivity to the tested settings are quantified relative to observations and using an ensemble approach. Persistent biases include overestimated SWnet_SFC and too intense hydrological cycle. However, model skill is mainly controlled by SW parameterization, especially the magnitude of SWnet_SFC and rainfall and both the spatial distribution and magnitude of latent heat fluxes over ocean. On the other hand, the spatial distribution of continental rainfall (SWnet_SFC) is mainly influenced by convection parameterization and horizontal resolution (boundary layer parameterization and orography). Physical understanding of the control of SW parameterization is addressed by analyzing the thermal structure of the atmosphere and conducting sensitivity experiments to O3 absorption and SW scattering coefficient. SW parameterization shapes the stability of the atmosphere in two different ways according to whether surface is coupled to atmosphere or not, while O3 absorption has minor effects in our simulations. Over SST-prescribed regions, increasing the amount of SW absorption warms the atmosphere only because surface temperatures are fixed, resulting in increased atmospheric stability. Over land–atmosphere coupled regions, increasing SW absorption warms both atmospheric and surface temperatures, leading to a shift towards a warmer state and a more intense hydrological cycle. This turns in reversal model behavior between land and sea points, with the SW scheme that simulates greatest SW absorption producing the most (less) intense hydrological cycle over land (sea) points. This demonstrates strong limitations for simulating land/sea contrasts in SST-forced simulations

Impurity-induced spin pseudogap in SrCuO₂ doped with Mg, Zn, or La

The low energy magnetic excitations spectra of the pristine and doped quasi-one-dimensional spin chains cuprates SrCuO2 have been investigated by inelastic neutron scattering. The momentum-integrated magnetic dynamical structure factor yields a constant integrated intensity with regard to energy in the pure compound, while it shows a strong decay, at low energies, in the compounds doped with nonmagnetic impurities, namely, SrCu0.99M0.01O2 (with M=Zn or Mg) and Sr0.99La0.01CuO2 (Cu+ carrying S=0 created within the chains). These results evidence the opening of a spin pseudogap in the two-spinon continuum of SrCuO2 upon doping, stemming from disruptions of the spin chains by quantum impurities

Impurity-induced spin pseudogap in SrCu O 2 doped with Mg, Zn, or La

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