Sunlight refraction in the mesosphere of Venus during the transit on June 8th, 2004     

P. Tanga  T. Widemann  B. Sicardy  J.M. Pasachoff  J. Arnaud  L. Comolli  A. Rondi  S. Rondi  P. Sütterlin 《Icarus》2012,218(1):207-219

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Thermospheric/mesospheric temperatures on Venus: Results from ground-based high-resolution spectroscopy of CO2 in 1990/1991 and comparison to results from 2009 and between other techniques     

Guido Sonnabend  Peter Krötz  Frank Schmülling  Theodor Kostiuk  Jeff Goldstein  Manuela Sornig  Dušan Stupar  Timothy Livengood  Tilak Hewagama  Kelly Fast  Arnaud Mahieux 《Icarus》2012,217(2):856-862

We report temperatures in Venus’ upper mesosphere/lower thermosphere, deduced from reanalyzing very high resolution infrared spectroscopy of CO₂ emission lines acquired in 1990 and 1991. Kinetic temperatures at ～110 km altitude (0.15 Pa) are derived from the Doppler width of fully-resolved single line profiles measured near 10.4 μm wavelength using the NASA GSFC Infrared Heterodyne Spectrometer (IRHS) at the NASA IRTF on Mauna Kea, HI, close to Venus inferior conjunction and two Venus solstices. Measured temperatures range from ～200 to 240 K with uncertainty typically less than 10 K. Temperatures retrieved from similar measurement in 2009 using the Cologne Tuneable Heterodyne Infrared Spectrometer (THIS) at the NOAO McMath Telescope at Kitt Peak, AZ are 10–20 K lower. Temperatures retrieved more recently from the SOIR instrument on Venus EXpress are consistent with these results when the geometry of observation is accounted for. It is difficult to compare ground-based sub-mm retrievals extrapolated to 110 km due to their much larger field of view, which includes the night side regions not accessible to infrared heterodyne observations. Temperature variability appears to be high on day-to-day as well as longer timescales. Observed short term and long term variability may be attributed to atmospheric dynamics, diurnal variability and changes over solar activity and seasons. The Venus International Reference Atmosphere (VIRA) model predicts cooler temperatures at the sampled altitudes in the lower thermosphere/upper mesosphere and is not consistent with these measurements.  相似文献   

Ardières-Morcille in the Beaujolais,France: A research catchment dedicated to study of the transport and impacts of diffuse agricultural pollution in rivers     

Véronique Gouy  Lucie Liger  Samira Ahrouch  Chloé Bonnineau  Nadia Carluer  Arnaud Chaumot  Marina Coquery  Aymeric Dabrin  Christelle Margoum  Stéphane Pesce 《水文研究》2021,35(10):e14384

The 8-km² Morcille catchment, which is a sub-catchment of the 150-km² Ardières catchment in the Beaujolais region of France, is one of the first sites in Europe where research has been conducted on surface water contamination by pesticides. A consolidated hydrological and chemical dataset has been set up with data collected since 2002 on the Morcille River and since 2011 on the Ardières River. Additional data on the ecotoxicological and ecological impacts of pesticides on aquatic microbial communities and macroinvertebrates has also been recorded in both rivers since 2005. The ‘Site Atelier Ardières-Morcille Dataset’ described here combines rainfall and stream water height measurements at gauged stations with concentrations of two trace elements and nine pesticides (mainly herbicides, fungicides and some of their metabolites) in both the Ardières and Morcille rivers. All contaminant concentration data showed spatial and temporal variability in water quality associated with pesticide use and rainfall patterns. This long-term monitoring framework made it possible to estimate the persistence of two herbicides (diuron and norflurazon) after legislation banning them. It took 4 years for diuron and more than 10 years for norflurazon concentrations to fall below 0.1 μg/L. Concurrent biological data showed a gradient of impacts consistent with chemical anthropogenic pressure, and rapid recovery of phototrophic microbial communities after the diuron ban. Finally, monitoring data on pesticide transport in a grassed strip set on a slope of the Morcille catchment confirmed that vegetative filter strips can effectively reduce diuron fluxes in surface runoff (>80% abatement) and infiltration water (>70% abatement). The full dataset offers a valuable resource for the validation of hydrological models and the development of global approaches to better understand the pressure–transport–exposure–impact chain and aquatic community resilience at the small catchment scale.  相似文献   

The influence of nearshore sand bank dynamics on shoreline evolution in a macrotidal coastal environment,Calais, northern France     

Arnaud Hequette  David Aernouts 《Continental Shelf Research》2010

Analyses of shoreline and bathymetry change near Calais, northern coast of France, showed that shoreline evolution during the 20th century was strongly related with shoreface and nearshore bathymetry variations. Coastal erosion generally corresponds to areas of nearshore seabed lowering while shoreline progradation is essentially associated with areas of seafloor aggradation, notably east of Calais where an extensive sand flat experienced seaward shoreline displacement up to more than 300 m between 1949 and 2000. Mapping of bathymetry changes since 1911 revealed that significant variation in nearshore morphology was caused by the onshore and alongshore migration of a prominent tidal sand bank that eventually welded to the shore. Comparison of bathymetry data showed that the volume of the bank increased by about 10×10⁷ m³ during the 20th century, indicating that the bank was acting as a sediment sink for some of the sand transiting alongshore in the coastal zone. Several lines of evidence show that the bank also represented a major sediment source for the prograding tidal flat, supplying significant amounts of sand to the accreting upper beach. Simulation of wave propagation using the SWAN wave model (Booij et al., 1999) suggests that the onshore movement of the sand bank resulted in a decrease of wave energy in the nearshore zone, leading to more dissipative conditions. Such conditions would have increased nearshore sediment supply, favoring aeolian dune development on the upper beach and shoreline progradation. Our results suggest that the onshore migration of nearshore sand banks may represent one of the most important, and possibly the primary mechanism responsible for supplying marine sand to beaches and coastal dunes in this macrotidal coastal environment.  相似文献   

In situ record of sedimentary processes near the Rhône River mouth during winter events (Gulf of Lions,Mediterranean Sea)     

C. Marion  F. Dufois  M. Arnaud  C. Vella 《Continental Shelf Research》2010

The environment is impacted by natural and anthropogenic disturbances that occur at different spatial and temporal scales, and that lead to major changes and even disequilibria when exceeding the resiliency capacities of the ecosystem. With an annual mean flow of 1700 m³ s⁻¹, the Rhône River is the largest of the western Mediterranean basin. Its annual solid discharges vary between 2 and 20 Mt, with flood events responsible for more than 70% of these amounts.  相似文献   

Did tillage erosion play a role in millennial scale landscape development?     

Jantiene E.M. Baartman  Arnaud J.A.M. Temme  Jeroen M. Schoorl  Michiel H.A. Braakhekke  Tom Veldkamp 《地球表面变化过程与地形》2012,37(15):1615-1626

Landscape evolution models (LEMs) quantitatively simulate processes of sedimentation and erosion on millennial timescales. An important aspect of human impact on erosion is sediment redistribution due to agriculture, referred to herein as tillage erosion. In this study we aim to analyse the potential contribution of tillage erosion to landscape development using LEM LAPSUS. The model is calibrated separately for a water erosion process (i) without tillage and (ii) with tillage. The model is applied to the ~250 km² Torrealvilla case study catchment, SE Spain. We were able to simulate alternating sequences of incision and aggradation, that are important on longer (millennial) timescales. Generally, model results show that tillage erosion adds to deposition in the lower floodplain area, but neither water erosion alone nor water with tillage erosion together could exactly reproduce the observed amounts of erosion and sedimentation for the case study area. In addition, scale effects are apparent. On hillslopes, tillage may contribute importantly to erosion and may fill local depressions. If assessed on the catchment scale, sediments from tillage erosion eventually reach the lower floodplain area where they contribute to deposition. However, water erosion was observed in the model simulations to be the most important process on the catchment scale. This is the first time that tillage erosion has been explicitly included in a landscape evolution model at a millennial timescale and large catchment scale. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Field Tracer Test for the Design of LNAPL Source Zone Surfactant Flushing          下载免费PDF全文

Thomas Robert  Richard Martel  René Lefebvre  Jean‐Marc Lauzon  Annie Morin 《Ground Water Monitoring & Remediation》2016,36(2):68-82

A field tracer test was carried out in a light nonaqueous phase liquid (LNAPL) source zone using a well pattern consisting of one injection well surrounded by four extraction wells (5‐spot well pattern). Multilevel sampling was carried out in two observation wells located inside the test cell characterized by heterogeneous lithology. Tracer breakthrough curves showed relatively uniform flow within soil layers. A numerical flow and solute transport model was calibrated on hydraulic heads and tracer breakthrough curves. The model was used to estimate an average accessible porosity of 0.115 for the swept zone and an average longitudinal dispersivity of 0.55 m. The model was further used to optimize the relative effects of viscous forces versus capillary forces under realistic imposed hydraulic gradients and to establish optimal surfactant solution properties. Maximum capillary number (N_Ca) values between injection and extraction wells were obtained for an injection flow rate of 16 L/min, a total extraction flow rate of 20 L/min, and a surfactant solution with a viscosity of 0.005 Pa?s. The unconfined nature of the aquifer limited further flow rate or viscosity increases that would have led to unrealistic hydraulic gradients. An N_Ca range of 3.8 × 10^?4 to 7.6 × 10^?3 was obtained depending on the magnitude of the simulated LNAPL‐water interfacial tension reduction. Finally, surfactant and chase water slug sizing was optimized with a radial form of the simplified Ogata‐Banks analytical solution (Ogata and Banks 1961) so that injected concentrations could be maintained in the entire 5‐spot cell.  相似文献   

An Analysis of Turbulent Heat Fluxes and the Energy Balance During the REFLEX Campaign     

Christiaan van der Tol  Wim Timmermans  Chiara Corbari  Arnaud Carrara  Joris Timmermans  Zhongbo Su 《Acta Geophysica》2015,63(6):1516-1539

Three eddy covariance stations were installed at the Barrax experimental farm during the Land-Atmosphere Exchanges (REFLEX) airborne training and measurement campaign to provide ground truth data of energy balance fluxes and vertical temperature and wind profiles. The energy balance closure ratio (EBR) was 105% for a homogeneous camelina site, 86% at a sparse reforestation site, and 73% for a vineyard. We hypothesize that the lower closure in the last site was related to the limited fetch. Incorporating a vertical gradient of soil thermal properties decreased the RMSE of the energy balance at the camelina site by 16 W m^?2. At the camelina site, eddy covariance estimates of sensible and latent heat fluxes could be reproduced well using mean vertical profiles of wind and temperature, provided that the Monin—Obukhov length is known. Measured surface temperature and sensible heat fluxes suggested high excess resistance for heat (kB^?1 = 17).  相似文献   

Crop area mapping in West Africa using landscape stratification of MODIS time series and comparison with existing global land products   总被引：6，自引：0，他引：6  

Elodie Vintrou  Annie DesbrosseAgnès Bégué  Sibiry TraoréChristian Baron  Danny Lo Seen 《International Journal of Applied Earth Observation and Geoinformation》2012,14(1):83-93

In Africa, food security early warning systems use satellite-derived data concerning crop conditions and agricultural production. Such systems can be improved if they are provided with a more reliable estimation of the cultivated area at national scale. This paper evaluates the potential of using time series from the MODerate resolution Imaging Spectroradiometer MOD13Q1 (16-day composite of normalized difference vegetation index at 250 m resolution) to extract cultivated areas in the fragmented rural landscapes of Mali. To this end, we first stratified Southern Mali into 13 rural landscapes based on the spatio-temporal variability of NDVI and textural indices, using an object-oriented classification scheme.The accuracy of the resulting map (MODIS_crop) and how it compares with existing coarse-resolution global land products (GLC2000 Africa, GLOBCOVER, MODIS V05 and ECOCLIMAP-II), was then assessed against six crop/non-crop maps derived from SPOT 2.5 m resolution images used as references. For crop areal coverage, the MODIS_crop cultivated map was successful in assessing the overall cultivated area at five out of the six validation sites (less than 6% of the absolute difference), while in terms of crop spatial distribution, the producer accuracy was between 33.1% and 80.8%. This accuracy was linearly correlated with the mean patch size index calculated on the SPOT crop maps (r² = 0.8). Using the Pareto boundary as an accuracy assessment method at the study sites, we showed that (i) 20-40% of the classification crop error was due to the spatial resolution of the MODIS sensor (250 m), and that (ii) compared to MODIS V05, which otherwise performed better than the other existing products, MODIS_crop generally minimized omission-commission errors. A spatial validation of the different products was carried out using SPOT image classifications as reference. In the corresponding error matrices, the fraction of correctly classified pixels for our product was 70%, compared to 58% for MODIS V05, while it ranged between 40% and 51% for the GLC2000, the ECOCLIMAP-II and the GLOBCOVER.  相似文献   

Surface studies of water isotopes in Antarctica for quantitative interpretation of deep ice core data     

Amaelle Landais  Mathieu Casado  Frédéric Prié  Olivier Magand  Laurent Arnaud  Alexey Ekaykin  Jean-Robert Petit  Ghislain Picard  Michel Fily  Bénédicte Minster  Alexandra Touzeau  Sentia Goursaud  Valérie Masson-Delmotte  Jean Jouzel  Anaïs Orsi 《Comptes Rendus Geoscience》2017,349(4):139-150

Polar ice cores are unique climate archives. Indeed, most of them have a continuous stratigraphy and present high temporal resolution of many climate variables in a single archive. While water isotopic records (δD or δ¹⁸O) in ice cores are often taken as references for past atmospheric temperature variations, their relationship to temperature is associated with a large uncertainty. Several reasons are invoked to explain the limitation of such an approach; in particular, post-deposition effects are important in East Antarctica because of the low accumulation rates. The strong influence of post-deposition processes highlights the need for surface polar research programs in addition to deep drilling programs. We present here new results on water isotopes from several recent surface programs, mostly over East Antarctica. Together with previously published data, the new data presented in this study have several implications for the climatic reconstructions based on ice core isotopic data: (1) The spatial relationship between surface mean temperature and mean snow isotopic composition over the first meters in depth can be explained quite straightforwardly using simple isotopic models tuned to d-excess vs. δ¹⁸O evolution in transects on the East Antarctic sector. The observed spatial slopes are significantly higher (～ 0.7–0.8‰·°C^?1 for δ¹⁸O vs. temperature) than seasonal slopes inferred from precipitation data at Vostok and Dome C (0.35 to 0.46‰·°C^?1). We explain these differences by changes in condensation versus surface temperature between summer and winter in the central East Antarctic plateau, where the inversion layer vanishes in summer. (2) Post-deposition effects linked to exchanges between the snow surface and the atmospheric water vapor lead to an evolution of δ¹⁸O in the surface snow, even in the absence of any precipitation event. This evolution preserves the positive correlation between the δ¹⁸O of snow and surface temperature, but is associated with a much slower δ¹⁸O-vs-temperature slope than the slope observed in the seasonal precipitation. (3) Post-deposition effects clearly limit the archiving of high-resolution (seasonal) climatic variability in the polar snow, but we suggest that sites with an accumulation rate of the order of 40 kg.m^?2.yr^?1 may record a seasonal cycle at shallow depths.  相似文献