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排序方式: 共有671条查询结果,搜索用时 15 毫秒
161.
Judith Fournier Antoine Thiboult Daniel F. Nadeau Nikki Vercauteren François Anctil Annie-Claude Parent Ian B. Strachan Alain Tremblay 《水文研究》2021,35(8):e14335
Hydrological models used for reservoir management typically lack an accurate representation of open-water evaporation and must be run in a scarce data context. This study aims to identify an accurate means to estimate reservoir evaporation with simple meteorological inputs during the open-water season, using long-term eddy covariance observations from two boreal hydropower reservoirs with contrasting morphometry as reference. Unlike the temperate water bodies on which the majority of other studies have focused, northern reservoirs are governed by three distinct periods: ice cover in the cold season, warming in the summer and energy release in the fall. The reservoirs of interest are Eastmain-1 (52°N, mean depth of 11 m) and Romaine-2 (51°N, mean depth of 42 m), both located in eastern Canada. Four approaches are analysed herein: a combination approach, a radiation-based approach, a mass-transfer approach, and empirical methods. Of all the approaches, the bulk transfer equation with a constant Dalton number of 1.2 x 10−3 gave the most accurate estimation of evaporation at hourly time steps, compared with the eddy covariance observations (RMSE of 0.06 mm h−1 at Eastmain-1 and RMSE of 0.04 mm h−1 at Romaine-2). The daily series also showed good accuracy (RMSE of 1.38 mm day−1 at Eastmain-1 and RMSE of 0.62 mm day−1 at Romaine-2) both in the warming and energy release phases of the open-water season. The bulk transfer equation, on the other hand, was incapable of reproducing condensation episodes that occurred soon after ice breakup. Basic and variance-based sensitivity analyses were conducted, in particular to measure the variation in performance when the bulk transfer equation was applied with meteorological observations collected at a certain distance (~10–30 km) from the reservoir. This exercise illustrated that accurate estimates of open water evaporation require representative measurements of wind speed and water surface temperature. 相似文献
162.
Nicolas Biver Dominique Bockelée-Morvan Jacques Crovisier Alain Lecacheux Gabriel Paubert Matthew Sumner Åke Hjalmarson Anders Winnberg Aage Sandqvist 《Icarus》2007,187(1):253-271
Comet 9P/Tempel 1 was the target of a multi-wavelength worldwide investigation in 2005. The NASA Deep Impact mission reached the comet on 4.24 July 2005, delivering a 370-kg impactor which hit the comet at 10.3 km s−1. Following this impact, a cloud of gas and dust was excavated from the comet nucleus. The comet was observed in 2005 prior to and after the impact, at 18-cm wavelength with the Nançay radio telescope, in the millimeter range with the IRAM and CSO radio telescopes, and at 557 GHz with the Odin satellite. OH observations at Nançay provided a 4-month monitoring of the outgassing of the comet from March to June, followed by the observation of H2O with Odin from June to August 2005. The peak of outgassing was found to be around between May and July. Observations conducted with the IRAM 30-m radio telescope in May and July 2005 resulted in detections of HCN, CH3OH and H2S with classical abundances relative to water (0.12, 2.7 and 0.5%, respectively). In addition, a variation of the HCN production rate with a period of 1.73±0.10 days was observed in May 2005, consistent with the 1.7-day rotation period of the nucleus. The phase of these variations, as well as those of CN seen in July by Jehin et al. [Jehin, E., Manfroid, J., Hutsemékers, D., Cochran, A.L., Arpigny, C., Jackson, W.M., Rauer, H., Schulz, R., Zucconi, J.-M., 2006. Astrophys. J. 641, L145-L148], is consistent with a rotation period of the nucleus of 1.715 days and a strong variation of the outgassing activity by a factor 3 from minimum to maximum. This also implies that the impact took place on the rising phase of the “natural” outgassing which reached its maximum ≈4 h after the impact. Post-impact observations at IRAM and CSO did not reveal a significant change of the outgassing rates and relative abundances, with the exception of CH3OH which may have been more abundant by up to one order of magnitude in the ejecta. Most other variations are linked to the intrinsic variability of the comet. The Odin satellite monitored nearly continuously the H2O line at 557 GHz during the 38 h following the impact on the 4th of July, in addition to weekly monitoring. Once the periodic variations related to the nucleus rotation are removed, a small increase of outgassing related to the impact is present, which corresponds to the release of ≈5000±2000 tons of water. Two other bursts of activity, also observed at other wavelengths, were seen on 23 June and 7 July; they correspond to even larger releases of gas. 相似文献
163.
Alain Cheilletz Dominique Gasquet Fouad Filali Douglas A. Archibald Massimo Nespolo 《Mineralium Deposita》2010,45(4):323-329
El Hammam is the only fluorite mine in Morocco (production 100,000 t/year). The fluorite mineralization is in an array of
fluorite–calcite veins and is characterized by unusually high REE content in carbonate minerals (1,400 ppm in calcite; up
to 2,000 ppm in siderite) and in fluorite (about 600 ppm). Since the 1960s, the genesis of the deposit has been attributed
to a mesothermal hydrothermal event connected with late-Variscan granitic intrusions. Precise 40Ar/39Ar dating of hydrothermal K-feldspar yields an age of formation of the El Hammam deposit at 205 ± 1 Ma. Its genesis is therefore
associated in time and space with the development of the Triassic–Jurassic basins and the associated anorogenic continental
flood basalts of the Moroccan Mesetian Middle Atlas. The source of the hydrothermal mineralization (magmatic and/or metamorphic)
is discussed. 相似文献
164.
This paper aims at studying the long-term orbital consequences of the perturbations related to De Haerdtl inequality, a current quasi-commensurability between the Galilean satellites of Jupiter Ganymede and Callisto. We used the method of Frequency Map Analysis to detect a chaotic behavior in a 5-bodies system where every inequality has been dropped, except of De Haerdtl one. We also used Frequency Analysis to draw the behavior of the arguments likely to become resonant, in several numerical integrations. We show that De Haerdtl inequality might have induced chaos in the past if Ganymede's and Callisto's eccentricities have been higher than 4×10−3. Moreover, we enlight the influence of Jupiter's obliquity on this chaos. We also enlight some aspects of this chaotic behavior, showing for instance stable chaos and single resonances. The main result of this study is that De Haerdtl inequality should be taken into account in every study of the long term orbital evolution of the Galilean satellites. 相似文献
165.
Quang Thanh Nguyen Sabine Caré Yves Berthaud Alain Millard Frédéric Ragueneau 《国际地质力学数值与分析法杂志》2011,35(10):1141-1159
Most reinforced concrete structures are damaged due to corrosion of reinforcements in concrete. In normal conditions the pH near the reinforcements is around 12–13 which means that steel is in a passive state. But aggressive species, such as chloride ions or carbon dioxide, may penetrate into concrete and promote active corrosion. As a consequence (hydro)oxides are produced leading to degradation of concrete structures. For instance cracking of the concrete is generated due to the pressure induced by rust. In this paper, we study the inception and the propagation of cracking on reinforced mortar plates with rebars located either in the middle or at the corner. Additional experiments have been performed on cylindrical specimens to determine the local effect of rust pressure at the interface rust/mortar. The specimens have been subjected to imposed current density in order to enhance the corrosion and digital image intercorrelation has been used to determine displacement fields. The experiments have been compared to numerical modelling. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
166.
We present experiments of upraising and relaxing topographies showing that peneplanation can occur above the ultimate base level (sea level). After active uplift, the erosion of a topography bounded by a piedmont generates a final smooth and highly elevated topography. Smoothing at high elevation is even possible during active uplift if the evolution of topography is disrupted by the deposition of the products of erosion on its piedmont which is the case at the transition from underfilled to overfilled conditions in foreland basins. 相似文献
167.
Both observational studies and numerical experiments demonstrate the sensitivity of the atmosphere to variations in the extent and mass of snow cover. There is therefore a need for simple but realistic snow parameterizations in forecast and climate models. This study describes a new physically-based snow hydrology for use in the Météo-France climate model, together with the ISBA land-surface scheme. A restricted number of parameters has been added, while preserving a single surface energy budget. The ageing process of the snow pack has been introduced through prognostic equations for snow density and snow albedo. Snowmelt computation has been modified over partially snow-covered and vegetated areas. The new scheme has been validated against field measurements in stand-alone simulations forced by observed meteorological conditions. The results show a strong improvement in the model's performance, thereby suggesting that a simple one-layer snow model is able to reproduce the main physical mechanisms governing the snow pack evolution. Part II of the present study will concern the validation in a 3-D experiment within the Météo-France climate model. 相似文献
168.
Alain Milhau 《Pure and Applied Geophysics》1970,81(1):246-262
Summary We propose a theoretical model based on the eddy diffusion which elucidates the polar conductivities repartition near the ground and the conductions current variations in relation with the altitude in the exchange layer. Investigations concerning the theoretical repartition of the electrical field and the space charge in relationwith the altitude were carried out and a method for calculating the diffusivity from electric parameters values (electric field, space charge, conductivity) near the ground surface has been elaborated. The diffusivity values thus obtained are compared with those deduced from the measurements of the thoron concentrations at different levels carried out on the same spot as the electric parameters measurements and at the same time.
Travail effectué dans le cadre d'un contrat CEA-Institute d'Optique Théorique et Appliquée. 相似文献
Travail effectué dans le cadre d'un contrat CEA-Institute d'Optique Théorique et Appliquée. 相似文献
169.
The primary goal of this investigation is to focus on a realistic scenario for simulating impacts on regional African climate of future deforestation in a greenhouse-warmed world. Combined effects of plausible land-cover change and greenhouse warming are assessed by time-slice simulations with an atmospheric general circulation model (AGCM) for the middle of the twenty first century. Three time-slice integrations have been performed with the ARPEGE-Climat AGCM incorporating a zooming technique to achieve a resolution of about 100 km over Africa. A control run for the current climate is forced by observed climatological sea surface temperatures (SSTs) and the observed vegetation distribution is specified from a new vegetation database, in order to improve the geographical distribution and properties of the vegetation cover. Future SST changes are derived from a transient coupled atmosphere–ocean simulation for scenario B2 of the International Panel on Climate Change (IPCC). Future vegetation changes are specified from a simulation of scenario B2 with the Integrated Model to Assess the Global Environment (IMAGE) developed at the National Institute of Public Health and the Environment in the Netherlands (RIVM). The results show that land surface processes can locally modulate greenhouse warming effects for African climate, with reductions of surface transpiration and small increases of surface temperature. Deforestation of tropical Africa has overall only a marginal effect on precipitation because of a compensatory increase in moisture convergence. Energy budget analyses show that increases in surface temperature are produced both by increases of greenhouse gases (GHG) concentration from the increase in downward atmospheric longwave radiation, and by African tropical deforestation from the resulting reduction in transpiration. This study indicates that realistic land-use changes, though of smaller amplitude than greenhouse gas forcing, may have a small regional effect in projections of future climate. 相似文献
170.
Aliakbar Baharifar Hossein Moinevaziri Herv Bellon Alain Piqu 《Comptes Rendus Geoscience》2004,336(16):1443-1452
The Hamadan area is characterised by various metamorphic rocks where the slates yielded Jurassic fossils. The entire column, representing the Mesozoic from at least the Jurassic to the Mid-Cretaceous, has been affected by tectono-metamorphic events and the emplacement of Late Cretaceous granitic rocks. A timing of these events is based on the 40K–40Ar ages carried mainly on separated amphiboles, biotites and muscovites, and interpreted as the ages of their isotopic closure. Results are ranging between 91 and 70 Ma. To cite this article: A. Baharifar et al., C. R. Geoscience 336 (2004).