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排序方式: 共有347条查询结果,搜索用时 15 毫秒
21.
U. Dayan B. Ziv A. Margalit E. Morin D. Sharon 《Theoretical and Applied Climatology》2001,69(1-2):103-122
Summary At times, a pronounced trough of low barometric pressure extends from equatorial Africa northward, over the Red Sea and the
eastern Mediterranean countries, i.e., the Red Sea Trough. The associated weather is usually hot and dry, and consequently
the atmosphere becomes conditionally unstable. In cases in which additional moisture is supplied and dynamic conditions become
supportive, as the case analyzed here, intense thunderstorms occur, with extreme rain rates, hail and floods.
The storm herein analyzed caused extensive damage both in casualties and property and evolved in two main consecutive phases:
In the first a Mesoscale Convective System that moved from Sinai northward over Israel dominated, and in the second deep convection
was organized mainly along a cold front.
Data analysis indicates several synoptic-scale factors that had a supportive effect on the storm formation and intensification:
Conditional instability established by the Red Sea trough, mid-level moisture transport from Northern Africa, and upper-level
divergence imparted by both polar and subtropical jet streams over the Middle-East.
Mesoscale features were further investigated by means of a hydro-meteorological observational analysis with high spatio-temporal
resolution using raingauge and radar data, and satellite imagery. It is shown that local factors, particularly topographic
effects, play a major role in the evolution, intensity and spatial organization of the convective activity.
Our findings support results of a numerical study of another autumn rainstorm associated with the Red Sea trough. In the present
case we identify an additional contributing factor, i.e., a mid-latitude upper-level trough that further intensified the storm
as it was approaching the Middle-East.
Received July 4, 2000 Revised January 16, 2001 相似文献
22.
The knowledge of the distribution functions of the order statistics for the Pearson III law and its derived forms is used for determining the confidence intervals associated with this law.This method is used to establish the tables and graphs for the confidence intervals of this law and its derived forms. 相似文献
23.
Guillaume Favreau Christian Leduc Christelle Marlin Abdou Guéro 《Comptes Rendus Geoscience》2002,334(6):395-401
In southwest Niger, the Continental Terminal water table displays a natural hollow shape about 10 m in depth over an area of 4000 km2. A 10-year survey of this hollow aquifer has shown that current recharge is above . The water table has risen continuously since the 1950–1960s as a result of land clearance. This shows a disequilibrium in the aquifer balance. The long-term recharge rate is estimated by radioisotopes to be around . This figure fits with the only possible origin of the piezometric depression, i.e. evapotranspiration losses in its centre. To cite this article: G. Favreau et al., C. R. Geoscience 334 (2002) 395–401. 相似文献
24.
André Burnol Francis Garrido Philippe Baranger Catherine Joulian Marie-Christine Dictor Françoise Bodénan Guillaume Morin Laurent Charlet 《Geochemical transactions》2007,8(1):12
High levels of arsenic in groundwater and drinking water are a major health problem. Although the processes controlling the
release of As are still not well known, the reductive dissolution of As-rich Fe oxyhydroxides has so far been a favorite hypothesis.
Decoupling between arsenic and iron redox transformations has been experimentally demonstrated, but not quantitatively interpreted.
Here, we report on incubation batch experiments run with As(V) sorbed on, or co-precipitated with, 2-line ferrihydrite. The
biotic and abiotic processes of As release were investigated by using wet chemistry, X-ray diffraction, X-ray absorption and
genomic techniques. The incubation experiments were carried out with a phosphate-rich growth medium and a community of Fe(III)-reducing
bacteria under strict anoxic conditions for two months. During the first month, the release of Fe(II) in the aqueous phase
amounted to only 3% to 10% of the total initial solid Fe concentration, whilst the total aqueous As remained almost constant
after an initial exchange with phosphate ions. During the second month, the aqueous Fe(II) concentration remained constant,
or even decreased, whereas the total quantity of As released to the solution accounted for 14% to 45% of the total initial
solid As concentration. At the end of the incubation, the aqueous-phase arsenic was present predominately as As(III) whilst
X-ray absorption spectroscopy indicated that more than 70% of the solid-phase arsenic was present as As(V). X-ray diffraction
revealed vivianite Fe(II)3(PO4)2.8H2O in some of the experiments. A biogeochemical model was then developed to simulate these aqueous- and solid-phase results.
The two main conclusions drawn from the model are that (1) As(V) is not reduced during the first incubation month with high
Eh values, but rather re-adsorbed onto the ferrihydrite surface, and this state remains until arsenic reduction is energetically
more favorable than iron reduction, and (2) the release of As during the second month is due to its reduction to the more
weakly adsorbed As(III) which cannot compete against carbonate ions for sorption onto ferrihydrite. The model was also successfully
applied to recent experimental results on the release of arsenic from Bengal delta sediments. 相似文献
25.
26.
Andre Guillaume 《Tectonophysics》1978,48(1-2)
This work discusses the state of knowledge (mainly tectonic and geophysical data) about the Tonale line and other “peri-Adriatic” lines in the Central and Eastern Alps. The chain is here cut into a mosaic of independent blocs, separated by faults with basic injections in some places. The Tonale fault had a dextral movement in Oligo-Miocene times; it is connected with the Austrian “Thermenlinie”, and not to the Pusteria—Gail line. An attempt at chronology is presented.
Résumé
Ce travail fait le point des connassiances, principalement tectoniques et géophysiques, sur la linge du Tonale et les accidents “péri-adriatiques” récents des Alpes centrales et Orientales. Dans cette région, la chaine est découpée en une mosaïque de blocs indépendants, séparés par des accidents injectés ça et là de masses basiques. L'accident du Tonale, Qui a joué en décrochement dextre à l'Oligo-Miocéne, est relié à la Thermenlinie d'Autriche Et non à la linge Pusteria—Gail. Un essai de chronologie est présenté. 相似文献27.
Yarrow Axford Camilla S. Andresen John T. Andrews Simon T. Belt Áslaug Geirsdóttir Guillaume Massé Gifford H. Miller Sædís Ólafsdóttir Lindsay L. Vare 《第四纪科学杂志》2011,26(6):645-656
Geochemical, mineralogical and biological indicators preserved in sediments are widely used to reconstruct past climate change, but proxies differ in the degree to which their utility as climate indicators has been validated via laboratory experiments, modern spatial calibrations, or down‐core comparisons with instrumental climate data. Multi‐proxy studies provide another means of evaluating interpretations of proxies. This paper presents a multi‐proxy assessment comparing 19 sub‐centennially resolved late Holocene proxy records, covering the period 300–1900 AD, from seven Icelandic marine and lacustrine core sites. We employ simple statistical comparisons between proxy reconstructions to evaluate their correlations over time and, ultimately, their utility as proxies for regional climate. Proxies examined include oxygen isotopic composition of benthic and planktonic foraminifera, abundance of the sea‐ice biomarker IP25, allochthonous quartz in marine sediments (a proxy for drift ice around Iceland), marine carbonate abundance, total organic carbon concentration, chironomid assemblages, lacustrine biogenic silica and carbon/nitrogen ratios in lake sediments. Most of the examined proxy records, including temperature and sea‐ice proxies, correlate strongly with each other over multi‐centennial timescales, and thus do appear to record changes in regional climate. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
28.
Sophie Raous Thierry Becquer Jérémie Garnier Éder de Souza Martins Guillaume Echevarria Thibault Sterckeman 《Applied Geochemistry》2010
An understanding of the biogeochemical behaviour of metals in mine spoil materials is a prerequisite to rehabilitate Ni mining sites. The objective of this study was to characterize the fate of metals in different Ni ore spoil materials as influenced by hydrological conditions and fertilisation practices. In tropical ultramafic complexes, the different stages of lateritic weathering lead to two types of ores, and therefore, to two spoil types. They are mainly either a clay-rich saprolite, so-called “garnierite”, enriched in phyllosilicates, or a limonitic material, enriched in Fe oxides. Lysimeter columns were designed to monitor leaching waters through both spoil materials. The garnieritic spoil released higher concentrations of Mg (mean = 2.25 mg L−1), Ni (0.39 mg L−1) and Cr (1.19 mg L−1) than the limonitic spoil (Mg = 0.5 mg L−1; Ni = 0.03 mg L−1 and Cr = 0.25 mg L−1). Chromium was mainly in an anionic form in leaching solutions. As exchangeable pools of Cr(VI) in limonite (980 mg kg−1 of KH2PO4-extractable Cr) are considerable its release in water may still occur in the case of a pH increase. In mixed spoil, metal concentrations were almost as low as in the limonitic one. The effect of mineral-N fertilisation was a strong release of cations (Ni, Mg) into the leachate. Phosphate amendment did not affect the soil solution composition under experimental conditions. 相似文献
29.
Adnand Bitri Jean-Pierre Brun Denis Gapais Florence Cagnard Charles Gumiaux Jean Chantraine Guillaume Martelet Catherine Truffert 《Comptes Rendus Geoscience》2010,342(6):448-452
We present results and interpretation of a 72 km long deep seismic reflection profile acquired across the internal zone of the Hercynian belt of South Brittany. The profile is of excellent quality, most of the crust being highly reflective. The “ARMOR 2 South” profile, is correlated with the “ARMOR 2 North” profile that was published in 2003. Correlation of the main subsurface reflections with surface geological and structural data provides important information about the crustal structure that resulted from thickening during Late Devonian and regional-scale extension during Late Carboniferous. In particular, seismics image shows a very high reflectivity zone, lying flat over more than 40 km at about 10–12 km depth. This zone is interpreted as a major zone of ductile crustal thinning. 相似文献
30.
Towards Stochastic Time-Varying Geological Modeling 总被引:3,自引:1,他引:2
Guillaume Caumon 《Mathematical Geosciences》2010,42(5):555-569
The modeling of subsurface geometry and properties is a key element to understand Earth processes and manage natural hazards
and resources. In this paper, we suggest this field should evolve beyond pure data fitting approaches by integrating geological
concepts to constrain interpretations or test their consistency. This process necessarily calls for adding the time dimension
to 3D modeling, both at the geological and human time scales. Also, instead of striving for one single best model, it is appropriate
to generate several possible subsurface models in order to convey a quantitative sense of uncertainty. Depending on the modeling
objective (e.g., quantification of natural resources, production forecast), this population of models can be ranked. Inverse
theory then provides a framework to validate (or rather invalidate) models which are not compatible with certain types of
observations. We review recent methods to better achieve both stochastic and time-varying geomodeling and advocate that the
application of inversion should rely not only on random field models, but also on geological concepts and parameters. 相似文献