Interaction between an eddy and a zonal jet : Part II. Two-and-a-half-layer model     

Frdric O. Vandermeirsch  Xavier J. Carton  Yves G. Morel 《Dynamics of Atmospheres and Oceans》2003,36(4):271-296

In a two-and-a-half-layer quasi-geostrophic model, a process study is conducted on the interaction between a vortex and a zonal jet, both with constant potential vorticity. The vortex is a stable anticyclone, initially located north of the eastward jet. The potential vorticity of the jet is allowed to have various vertical structures, while the vortex is concentrated in only one layer. The flow parameters are set to values characteristic of the Azores region.First, the jet is stable. Weak vortices steadily drift north of the jet without crossing it while strong vortices can cross the jet and tear off a cyclone with which they pair as a heton (baroclinic dipole). This heton often breaks later in the shear exerted by the jet; the two vortices finally drift apart. When crossed by deep anticyclones, the jet develops meanders with 375 km wavelength. These results exhibit a noticeable similarity with the one-and-a-half-layer case studied in Part I.Secondly, the jet is allowed to be linearly unstable. In the absence of the vortex, it develops meanders with 175 km wavelength and 25-day e-folding time on the β-plane. For various vertical structures of the jet, baroclinic instability is shown to barely affect jet–vortex interaction if the linear growth rate of unstable waves is smaller than 1/(14 days). Further simulations with a linearly unstable, nonlinearly equilibrated jet evidence its strong temporal variability when crossed by a deep vortex on the β-plane. In particular, long waves can dominate the spectrum for a few months after jet crossing by the vortex. Again in this process, the deep vortex couples with a surface cyclone and both drift southwestward.  相似文献   

Methane and carbon dioxide adsorption–diffusion experiments on coal: upscaling and modeling     

Andreas Busch  Yves Gensterblum  Bernhard M. Krooss  Ralf Littke 《International Journal of Coal Geology》2004,60(2-4):151-168

Numerical modelling of the processes of CO₂ storage in coal and enhanced coalbed methane (ECBM) production requires information on the kinetics of adsorption and desorption processes. In order to address this issue, the sorption kinetics of CO₂ and CH₄ were studied on a high volatile bituminous Pennsylvanian (Upper Carboniferous) coal (VR_r=0.68%) from the Upper Silesian Basin of Poland in the dry and moisture-equilibrated states. The experiments were conducted on six different grain size fractions, ranging from <0.063 to 3 mm at temperatures of 45 and 32 °C, using a volumetric experimental setup. CO₂ sorption was consistently faster than CH₄ sorption under all experimental conditions. For moist coals, sorption rates of both gases were reduced by a factor of more than 2 with respect to dry coals and the sorption rate was found to be positively correlated with temperature. Generally, adsorption rates decreased with increasing grain size for all experimental conditions.Based on the experimental results, simple bidisperse modelling approaches are proposed for the sorption kinetics of CO₂ and CH₄ that may be readily implemented into reservoir simulators. These approaches consider the combination of two first-order reactions and provide, in contrast to the unipore model, a perfect fit of the experimental pressure decay curves. The results of this modeling approach show that the experimental data can be interpreted in terms of a fast and a slow sorption process. Half-life sorption times as well as the percentage of sorption capacity attributed to each of the two individual steps have been calculated.Further, it was shown that an upscaling of the experimental and modelling results for CO₂ and CH₄ can be achieved by performing experiments on different grain size fractions under the same experimental conditions.In addition to the sorption kinetics, sorption isotherms of the samples with different grain size fractions have been related to the variations in ash and maceral composition of the different grain size fractions.  相似文献   

Geology and mineral potential of Ethiopia: a note on geology and mineral map of Ethiopia   总被引：1，自引：0，他引：1  

Solomon Tadesse  Jean-Pierre Milesi  Yves Deschamps   《Journal of African Earth Sciences》2003,36(4):273-313

This work presents a geoscientific map and database for geology, mineral and energy resources of Ethiopia in a digital form at a scale of 1:2,000,000, compiled from several sources. The final result of the work has been recorded on CD-ROM in GIS format so that the map and the database could be available to users on a personal computer.Metallic resources (precious, rare, base and ferrous–ferroalloy metals) are widely related to the metamorphic meta-volcano-sedimentary belts and associated intrusives belonging to various terranes of the Arabian–Nubian Shield, accreted during the East and West Gondwana collision (Neoproterozoic, 900–500 Ma).Industrial minerals and rock resources occur in more diversified geological environments, including the Proterozoic basement rocks, the Late Paleozoic to Mesozoic sediments and recent (Cenozoic) volcanics and associated sediments.Energy resources (oil, coal, geothermal resources) are restricted to Phanerozoic basin sediments and Cenozoic volcanism and rifting areas.  相似文献   

Potential control of climatic changes on flood events in the Yangtze Delta during 1100-2002     

JIANG Tong  ZHANG Qiang  Yves GUERNOND 《地理学报(英文版)》2004,14(1):70-80

1IntroductionClimatic warming, flood hazards and their impacts on human society receive increasing attention from governments and public (IPCC, 2001). During recent years, agriculture, industry and even the development of the whole national economy suffered tremendous loss resulted from flood and waterlogging hazards.The Yangtze Delta is densely populated and economically developed. Monsoonal climate, geomorphologic characteristics and human activities inflict floods and water-logging hazar…  相似文献   

From modelling to experiment     

Yves Guermond  Daniel Delahaye  Edwige Dubos-Paillard  Patrice Langlois 《GeoJournal》2004,59(3):171-176

Mathematical models applied to urban and regional planning have been widely developed during the sixties. Since that time the scientific and technologic developments have deeply transformed the field of spatial modelling. There has been a reaction against the idea that reality could be reduced to deterministic models. The paradigms of complexity, chaos, self-organisation, fractal geometry have made obvious the unpredictability of complex socio-economic systems. At the same time the progress of computation has led to the substitution of simulation methods to analytic solutions of mathematical models. In such a context, models are loosing in generality and reproducibility what they earn in adaptation to empirical situations. An important challenge is also to confirm the pertinence and specificity of the geographical approach. In that respect the spatial analysis programs must prove the evidence of a common methodology dealing either with physical or human and economic domain. We are working, for instance, on cellular automata programs applied to the historical evolution of an urban space and also to the run-off process in an elementary basin. The spatial structure of the models may be slightly different: rectangular or hexagonal tessellations in the “Human Geography” program, TIN structure, closer to the physical reality, in the other. The relations between the cells may also differ: they are often defined by a distance matrix for the socio-economic models, but a contiguity matrix is of course needed for the streaming process. But, beyond these technical differences, it appears that the geographical programs are developed on a macro-level, that is on aggregate statistical units. The elementary particle is always (or should be for a geographer...) a material, spatial unit, unlike the drop of water of the hydrologists, or the individual “agents” of the sociologists' multi-agents systems. The difference between the micro and macro level is not a question of scale, but a difference of logic. The simulation approach has a requisite, which is a need of systematic validation by a permanent comparison with the actual situation, but the objective is not prediction. The scientific concern is, before all, a precise understanding of the past and recent evolutions, more than a forecasting, which escapes to the specific field of scientific research. What is scientific is what can be measured. The possible prediction may rely on the scientific research, but belongs strictly to the domain of intellectual and personal thinking. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Morphological and speleothemic development in Brujas Cave (Southern Andean Range, Argentine): palaeoenvironmental significance     

Carlos Sancho  Jos Luis Pea  Raúl Mikkan  Cinta Oscar  Yves Quinif 《Geomorphology》2004,57(3-4):367-384

Brujas Cave, in the Southern Andean Range, is a well-known endokarstic site in Argentina. However, the origin and evolution of this cave system are poorly known. Based on morphological cave features as well as characteristics of cave deposits, we propose a meteogene drawdown cave genesis, including a change from phreatic to vadose conditions related to the high rate of fluvial downcutting in the area. During the vadose period, various cave-related deposits, including authogenic calcite and gypsum speleothems, allogenic volcanic ash and external tufas were deposited. Gypsum crusts are the oldest cave deposits identified (90.2–64.3 ky BP). Their origin, deduced from isotopic characteristics (∂³⁴S=9.6‰), is related to the oxidation of pyrite contained in the Jurassic limestone bedrock as well as the dissolution of overlying Jurassic–Triassic evaporite formations. Gypsum crust deposition is associated with evaporation of water flowing and seeping into the cave during arid environmental conditions. Calcite deposits precipitated from flowing water under equilibrium conditions represent the main speleothem growth period (67.6–34 ky BP in age). Their stable isotope values (∂¹³C=−3‰ to −5‰ and ∂¹⁸O=−9‰ to −11‰) may indicate slightly humid and warm conditions related to the regional Minchin lacustrine phase and global oxygen isotope stage 3. Following this stage, a seismic event is evidenced by accumulations of broken stalactites. Seepage calcite speleothems covering cave walls were deposited under disequilibrium conditions by evaporation, probably during Holocene time. Finally, another more recent gypsum deposition period represented by gypsum balls has been differentiated. Micromorphological as well as isotopic (∂³⁴S=5.6‰) data indicate that these gypsum forms are related to cyclic processes (solution–deposition) from water seeping into the cave under arid conditions. In addition, intense volcanic activity in the area during Holocene time is deduced from allogenic volcanic ash and lapilli located mainly at the entrance cave. At present, limited hydrological activity is observed in the cave and small tufa deposits at karstic discharge points are evidenced. We conclude that the geomorphological evolution of Brujas Cave was controlled by climatic changes (wet and dry stages) under semiarid environmental conditions in a very active tectonic and volcanic setting during Late Quaternary time.  相似文献   

Diatom taxonomic and morphological changes as indicators of metal pollution and recovery in Lac Dufault (Québec, Canada)     

Antonella Cattaneo  Yves Couillard  Sybille Wunsam  Michel Courcelles 《Journal of Paleolimnology》2004,32(2):163-175

We studied diatom taxonomic composition and the presence of morphological alterations (size and deformations) along a sediment core collected in Lac Dufault, Abitibi, whose watershed has a long history of mining pollution presently undergoing mitigation. According to sediment dating with ²¹⁰Pb and metal profiles along the core, we could identify four periods in the contamination history of the lake, which were characterized by different diatoms. Tabellaria flocculosa was dominant in the pre-mining period but was drastically reduced at the onset of pollution when Fragilaria cf. tenera became important. This diatom, together with other Fragilaria species and cysts of Chaetoceros muelleri, typified the transition period in which Cu reached its maximum value and other metals started to increase. During the period of maximum contamination with Zn, Cd, and Fe accompanied by acid mine drainage, Achnanthes minutissima and Brachysira vitrea were dominant. These taxa started to wane in the most recent sediments representing a partial chemical recovery. Asterionella formosa, which almost vanished at mining onset, reappeared with high abundance in these superficial sections. Beside these taxonomical shifts, we observed during the contamination period significant reduction in valve length together with increased percentages of valve deformations. Because available data on water chemistry and a diatom-based pH reconstruction suggest that Lac Dufault escaped severe acidification, diatom patterns observed in the core can be mostly ascribed to metal contamination. Individual diatom abundance and valve length had strong statistical relationships with the different metals identified in the core. Diatom changes both taxonomic and morphological can be excellent specific indicator of metal contamination and early recovery.  相似文献   

Relationships among Gibbs free energies and enthalpies of formation of phosphates,oxides and aqueous ions     

Yves Tardy  Philippe Vieillard 《Contributions to Mineralogy and Petrology》1977,63(1):75-88

Two parameters _GO^2– and _HO^2– are defined as the differences between respectively the Gibbs free energies and the enthalpies of formation of an oxide and its corresponding aqueous cation. The Gibbs free energies and enthalpies of formation of phosphates from their consituent oxides are shown to be linear functions of respectively _GO^2– and _HO^2– of their constituent cations.  相似文献   

Relationships among Gibbs energies of formation of sulfates,nitrates, carbonates,oxides and aqueous ions     

Yves Tardy  Lucienne Gartner 《Contributions to Mineralogy and Petrology》1977,63(1):89-102

A parameter _GO^2– is defined as the difference between the Gibbs free energy of formation from the elements of a given oxide and its corresponding aqueous cation. The Gibbs free energies of formation of compounds such as sulfates, nitrates or carbonates, from their constituent oxides, are shown to be linear functions of _GO^2– values of their constituent cations.  相似文献   

Stabilization of complex ions by the crystal field: CO 3 2− , NO 3 − , O 3 − , [(OH)4]4−, [(OH)3F]4−, [(OH)2F2]4−     

André Julg  Yves Ozias 《Physics and Chemistry of Minerals》1985,12(5):307-310

According to Koopmans' theorem, only the electrons associated with molecular levels of negative energy are stable. Many ions which cannot exist in the isolated state because certain occupied levels are positive, become stable in crystals under the stabilization effect arising from the crystal field. As examples, we have studied CO ₃ ^2? in calcite, NO ₃ ^? in NaNO₃, and several natural limpurities: O ₃ ^? in fluorite, [(OH)₄]^4?, [(OH)₃F]^4? and [(OH)₂F₂]^4? in zircon and thorite, by means of the molecular self-consistent field, the crystal field being simulated by point charges. As expected, all the energies corresponding to the occupied levels are negative within the crystal field, contrary to what occurs in the isolated state. Informations concerning the structure and the size of the critical germ are obtained for CaCO₃ and NaNO₃.  相似文献