Anthropogenic climate change over the Mediterranean region simulated by a global variable resolution model   总被引：1，自引：2，他引：1  

A.-L. Gibelin  M. Déqué 《Climate Dynamics》2003,20(4):327-339

Two 30-year simulations corresponding to 1960-1989 and 2070-2099 have been performed with a variable resolution atmospheric model. The model has a maximum horizontal resolution of 0.5° over the Mediterranean Sea. Simulations are driven by IPCC-B2 scenario radiative forcing. Sea surface temperatures (SSTs) are prescribed from monthly observations for the present climate simulation, and from a blend of observations and coupled simulations for the scenario. Another pair of forced atmospheric simulations has been run under these forcings with the same uniform low resolution as the coupled model. Comparisons with observations show that the variable resolution model realistically reproduces the main climate characteristics of the Mediterranean region. At a global scale, changes in latitudinal temperature profiles are similar for the forced and coupled models, justifying the time-slice approach. The 2 m temperature and precipitation responses predict a warming and drying of the Mediterranean region. A comparison with the coupled simulation and forced low-resolution simulation shows that this pattern is robust. The decrease in mean precipitation is associated with a significant decrease in soil wetness, and could involve considerable impact on water resources around the Mediterranean basin.  相似文献   

In-situ Formation of Light-Absorbing Organic Matter in Cloud Water   总被引：1，自引：0，他引：1  

A. Gelencsér  A. Hoffer  G. Kiss  E. Tombácz  R. Kurdi  L. Bencze 《Journal of Atmospheric Chemistry》2003,45(1):25-33

Current climate models seem to underestimate the flux of solar energy absorbed by the global troposphere. All of these models are constrained with the assumption that cloud droplets consist of pure water. Here we demonstrate in a simple laboratory experiment that aromatic hydroxy-acids which are found in continental fine aerosol can react with hydroxyl radicals under typical conditions prevalent in cloud water influenced by biomass burning. The reactions yield colored organic species which do absorb solar radiation. We also suggest that the products of such reactions may be humic-like substances whose presence in continental aerosol has been confirmed but their source mechanisms are still much sought after. We also attempt to give a first order estimate of the enhancement of water absorption at a visible wavelength under atmospheric conditions.  相似文献   

Synoptic and mesoscale study of a severe convective outbreak with the nonhydrostatic Global Environmental Multiscale (GEM) model   总被引：1，自引：0，他引：1  

A. Erfani  A. Méthot  R. Goodson  S. Bélair  K.-S. Yeh  J. Côté  R. Moffet 《Meteorology and Atmospheric Physics》2003,82(1-4):31-53

Summary ?A nonhydrostatic 4-km version of the Global Environmental Multiscale (GEM) model, with detailed microphysics included, was used to forecast the initiation, development, and structure of a tornado-producing supercell storm that occurred near Pine Lake (Alberta, Canada) on 15 July 2000. Examination of observations and comparison with conceptual models indicate that this storm is a good example of supercell storms that regularly produce summertime severe weather over Alberta. It was found that the high-resolution model was able to reproduce the early initiation of convective activity along the Rocky Mountains foothills, as well as the rapid northeastward propagation towards the Pine Lake area and the subsequent intensification into a supercell storm. The general structures of the forecasted convective system correspond well with conceptual representations of such events. Overall, this high-resolution forecast of the Pine Lake supercell storm was a significant improvement over the current operational version of the GEM model (24 km), which was not able to intensify the foothills’ convection into a supercell storm. Finally, it was found that the nonhydrostatic version of the model produces better trajectory and propagation speed of the convective system, as compared with the hydrostatic one. Received March 20, 2001; revised August 24, 2001  相似文献   

中国北部边疆第四系地下水研究     

李国安  韩朝平 《第四纪研究》1996,16(2):105-114

在中国北部边疆西起天山东端的北山，东至大兴安岭北段的４２００ｋｍ地域内，气候干旱少雨，水资源贫乏，第四系地下水是主要供水源之一。本文首次比较系统地研究了该区第四纪堆积物的分布和地下水的赋存规律。文中依据不同地貌单元、地层岩性及气候条件诸因素将本区第四系地下水划分为枝状沟谷砂砾石层孔隙水、河谷冲积平原砂砾石层孔隙水两种主要类型，并着重对有重要供水意义的河谷冲积平原砂砾石层孔隙水的分布、埋藏条件、富水性及水化学特征进行了论述。  相似文献   

Transport in a 2-D saturated porous medium: A new method for particle tracking   总被引：2，自引：0，他引：2  

Frédérick Delay  Hélène Housset-Resche  Gilles Porel  Ghislain de Marsily 《Mathematical Geology》1996,28(1):45-71

A new method for solving the transport equation based on the management of a large numbe of particles in a discretized 2-D domain is presented. The method uses numerical variables to represent the number of particles in a given mesh and is more complex than the 1-D problem. The first part of the paper focuses on the specific management of particles in a 2-D problem. The method also would be valid for three dimensions as long as the medium can be modeled similar to a layered system. As the particles are no longer tracked individually, the algorithm is fast and does not depend on the number of particles present. The numerical tests show that the method is nearly numerical dispersion free and permits accurate calculations even for simulations of low-concentration transport. Because each mesh is considered as a closed system between two successive time steps, it is easy to add adsorption phenomenon without any problem of numerical stability. The model is tested under conditions that are extremely demanding for its operating mode and gives a good fit to analytical solutions. The conditions in which it can be used to best advantage are discussed.  相似文献   

The age and thermal history of Cerro Rico de Potosi, Bolivia   总被引：1，自引：0，他引：1  

C. G. Cunningham  R. E. Zartman  E. H. McKee  R. O. Rye  C. W. Naeser  O. Sanjinés V  G. E. Ericksen  F. Tavera V 《Mineralium Deposita》1996,31(5):374-385

 Cerro Rico de Potosi, Bolivia, is the world’s largest silver deposit and has been mined since the sixteenth century for silver, and for tin and zinc during the twentieth century, together with by-product copper and lead. The deposit consists primarily of veins that cut an altered igneous body that we interpret to be a dacitic volcanic dome and its underlying tuff ring and explosion breccia. The deposit is compositionally and thermally zoned, having a core of cassiterite, wolframite, bismuthinite, and arsenopyrite surrounded by a peripheral, lower-temperature mineral assemblage consisting principally of sphalerite, galena, lead sulfosalt, and silver minerals. The low-temperature assemblage also was superimposed on the high-temperature assemblage in response to cooling of the main hydrothermal system. Both the dacite dome and the ore fluids were derived from a larger magmatic/hydrothermal source at depth. The dome was repeatedly fractured by recurrent movement on the fault system that guided its initial emplacement. The dome was extruded at 13.8±0.2 Ma (2σ), based on U-Th-Pb dating of zircon. Mineralization and alteration occurred within about 0.3 my of dome emplacement, as indicated by a ⁴⁰Ar/³⁹Ar date of 13.76±0.10 Ma (1σ) for sericite from the pervasive quartz-sericite-pyrite alteration associated with the main-stage, high-temperature, mineralization. The last thermal event able to reset zircon fission tracks occurred no later than 12.5±1.1 Ma (1σ), as indicated by fission-tract dating. Minor sericite, and magmatic-steam alunite veins, were episodically formed around 11 Ma and between 8.3 and 5.7 Ma; the younger episodes occurring at the time of extensional fracturing at Cerro Rico and widespread volcanism in the adjacent Los Frailes volcanic field. None of these younger events appear to be significant thermal/mineralizing events; the exceptionally flat thermal release pattern of ³⁹Ar from sericite and the results of the fission-tract dating of zircon show that none of the younger events was hot enough, and lasted long enough, to cause significant loss of Ar or annealing of zircon fission tracks. U-Th-Pb dating of zircon cores indicates a Precambrian progenitor for some zircons, and REE analyses of dated samples of hydrothermally altered dacite show the presence of a prominent positive Eu anomaly, which constrains interpretations of the origin and evolution of the magmatic/hydrothermal system. Received: 14 October 1995/Accepted: 29 January 1996  相似文献   

The replacement of anthophyllite by jimthompsonite: a model for hydration reactions in biopyriboles     

Bernard Henry Grobéty 《Contributions to Mineralogy and Petrology》1997,127(3):237-247

Anthophyllite crystals found in ultramafic lenses of the Lepontine Alps (Switzerland) contain coherent, submicroscopic intergrowths of ordered and disordered biopyribole polysomes. The chain width distributions of disordered polysomes were analyzed using high resolution transmission electron microscopy (HRTEM). Chains wider than triple were interpreted as intermediate products in the transformation of anthophyllite to the triple chain silicate jimthompsonite. The concentration of individual chain types is strongly correlated with the reaction progress. Based on observed zipper terminations and the transformation rules given by Veblen and Buseck (1980) a scheme of possible reaction paths leading from anthophyllite to jimthomp sonite is proposed. The reaction scheme and a simple kinetic model for elementary reactions allow modeling of the observed chain width distributions. The model suggests that the complex reaction paths involving steps with increasing and decreasing chain width are more important in the formation of jimthompsonite than the direct transformation from anthophyllite. The wide chains (>triple) occurring as intermediate products of the multi-step paths are structurally closer to talc than jimthompsonite. The back-transformation of these wide chains to triple chains is, therefore, a strong argument that jimthompsonite is a stable phase and not only a metastable intermediate product in the transformation of anthophyllite to talc. Received: 8 July 1996 / Accepted: 13 December 1996  相似文献   

Methodical approach to distribution of epilithic and drifting algae communities in a French subalpine river: Inferences on water quality assessment   总被引：2，自引：0，他引：2  

Thierry Rolland  Stéphanie Fayolle  Arlette Cazaubon  Stéphane Pagnetti 《Aquatic Sciences - Research Across Boundaries》1997,59(1):57-73

In a sub-alpine river, the Asse, with an unpredictable discharge regime, chlorophyll, density and taxonomic diversity of both drifting and periphytic communities were studied from a methodical approach. The investigations based on stamping two close cross-sections to know their spatial distributions in a heterogeneous bed substrate showed a heterogeneous pattern of colonization mainly influenced by hydrological variables as the current velocity, the size of the substrata (gravel-pebble-boulder). For the drifting algae, mainly composed with benthic species temporarily unhooked to the substrata, the heterogeneity of the distribution was reduced in fast flow which induced a mixing of the whole mass of water. For the periphyton, some results indicated that the greatest diversity and the highest chlorophyll concentration were found on pebble substratum where the current velocity was moderate. These results have also shown that the classical methods used to day for investigations were inadequate for most Mediterranean rivers. It was really difficult to estimate the water quality from classical index created for use in regular large plain rivers.  相似文献   

Editorial Special Topic     

Denis Alcaydé 《Annales Geophysicae》1997,14(12):1233-1233

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Nonlinear Shallow Water Theories for Coastal Waves     

Eric Barthélemy 《Surveys in Geophysics》2004,25(3-4):315-337

Ocean waves entering the near-shore zone undergo nonlinear and dispersive processes. This paper reviews nonlinear models, focusing on the so-called Serre equations. Techniques to overcome their limitations with respect to the phase speed are presented. Nonlinear behaviours are compared with theoretical results concerning the properties of Stokes waves. In addition, the models are tested against experiments concerning periodic wave transformation over a bar topography and of the shoaling of solitary waves on a beach.  相似文献