On the Influence of a Simple Microphysics Parametrization on Radiation Fog Modelling: A Case Study During ParisFog     

Xiaojing Zhang  Luc Musson-Genon  Eric Dupont  Maya Milliez  Bertrand Carissimo 《Boundary-Layer Meteorology》2014,151(2):293-315

A detailed numerical simulation of a radiation fog event with a single column model is presented, which takes into account recent developments in microphysical parametrizations. One-dimensional simulations are performed using the computational fluid dynamics model Code_Saturne and the results are compared to a very detailed in situ dataset collected during the ParisFog campaign, which took place near Paris, France, during the winter 2006–2007. Special attention is given to the detailed and complete diurnal simulations and to the role of microphysics in the fog life cycle. The comparison between the simulated and the observed visibility, in the single-column model case study, shows that the evolution of radiation fog is correctly simulated. Sensitivity simulations show that fog development and dissipation are sensitive to the droplet-size distribution through sedimentation/deposition processes but the aerosol number concentration in the coarse mode has a low impact on the time of fog formation.  相似文献   

Brick and tile clay mining from the paddy lands of Central Kerala (southwest coast of India) and emerging environmental issues     

V. Santhosh  D. Padmalal  B. Baijulal  K. Maya 《Environmental Earth Sciences》2013,68(7):2111-2121

The increasing demand for building materials has led to indiscriminate exploitation of clay-rich topsoil from wetlands including the paddy lands of Central Kerala in the southwestern coast of India. The problem is critical in areas adjoining the major developmental centers having low per capita land and natural resource availability. Loss of fertile topsoil, shrinkage of agricultural lands and consequent food security issues, erosion of naturally evolved nutrients, lowering of water table in wells adjacent to the mining sites, etc., are some of the major environmental issues arising from indiscriminate brick and tile clay mining. Although, brick and tile clay mining brings short-term economic benefits and employment opportunities to a section of people, the process in the long run creates severe damages to the environmental settings of the area. The present paper deals with a few aspects of brick and tile clay mining in the paddy lands of Central Kerala, especially around Kochi City, a fast developing urban-cum-industrial center in South India, which demands large quantities of building materials including bricks and tiles for construction of infrastructural facilities. It is estimated that 729,695 tons/year (ty^?1) of brick and tile clays are extracted from the coastal lowlands of Central Kerala, spreading to the Chalakudy (135,975 ty^?1), Periyar (483,820 ty^?1) and Muvattupuzha (109,900 ty^?1) river basins. The N, P and K loss through extraction of brick and tile clays amounts to 210 ty^?1, 96 ty^?1 and 9,352 ty^?1, respectively. As nutrient loss is an irreversible process in human time scale, its implications on agricultural productivity is a matter of serious concern. The study warrants the need for a comprehensive policy with an aim to regulate the mining activities on an environment- friendly basis in the densely populated coasts of the world, in general, and the study area in particular.  相似文献   

A comparison of instrumental dewatering methods for the separation and concentration of suspended sediment for subsequent trace element analysis     

A. J. Horowitz  K. A. Elrick  R. C. Hooper 《水文研究》1989,3(2):163-184

A comparison involving both field and laboratory trials was performed to evaluate the utility of two continuous-flow centrifuges and a tangential-flow filtration system for dewatering suspended sediments for subsequent trace element analysis. Although recovery efficiencies for the various devices differ, the analytical results from the separated suspended sediments indicate that any of the tested units can be used effectively and precisely for dewatering. Further, the three devices appear to concentrate and dewater suspended sediments in such a manner as to be equivalent to that which could be obtained by in-line filtration. Only the tangential-flow filtration system appears capable of providing both a dewatered sediment sample and a potentially usable effluent, which can be analysed for dissolved trace elements. The continuous-flow centrifuges can process whole water at an influent feed rate of 41 per minute; however, when suspended sediment concentrations are low (<30mg^?1), when small volumes of whole water are to be processed (30 to 401), or when suspended sediment mean grain size is very fine (<10 μm), influent feed rates of 21 per minute may be more efficient. Tangential-flow filtration can be used to process samples at the rate of 11 per minute.  相似文献   

Monitoring urban impacts on suspended sediment,trace element,and nutrient fluxes within the City of Atlanta,Georgia, USA: program design,methodological considerations,and initial results     

Arthur J. Horowitz  Kent A. Elrick  James J. Smith 《水文研究》2008,22(10):1473-1496

Atlanta, Georgia (City of Atlanta, COA), is one of the most rapidly growing urban areas in the US. Beginning in 2003, the US Geological Survey established a long‐term water‐quantity/quality monitoring network for the COA. The results obtained during the first 2 years have provided insights into the requirements needed to determine the extent of urban impacts on water quality, especially in terms of estimating the annual fluxes of suspended sediment, trace/major elements, and nutrients. During 2004/2005, suspended sediment fluxes from the City of Atlanta (COA) amounted to about 150 000 t year^?1; ≥ 94% of the transport occurred in conjunction with storm‐flow, which also accounted for ≥ 65% of the annual discharge. Typically, storm‐flow averaged ≤20% of the year. Normally, annual suspended sediment fluxes are determined by summing daily loads based on a single calculation step using mean‐daily discharge and a single rating curve‐derived suspended sediment concentration. Due to the small and ‘flashy’ nature of the COAs streams, this approach could produce underestimates ranging from 25% to 64%. Accurate estimates ( ± 15%) require calculation time‐steps as short as every 2–3 h. Based on annual median base‐flow/storm‐flow chemical concentrations, the annual fluxes of ≥ 75% of trace elements (e.g. Cu, Pb, Zn), major elements (e.g. Fe, Al), and total P occur in association with suspended sediment; in turn, ≥ 90% of the transport of these constituents occur in conjunction with storm‐flow. As such, base‐flow sediment‐associated and dissolved contributions represent relatively insignificant portions of the total annual load. An exception is total N, whose sediment‐associated fluxes range from 50% to 60%; even so, storm‐related transport typically exceeds 80%. Hence, in urban environments, non‐point‐sources appear to be the dominant contributors to the fluxes of these constituents. Published in 2007by John Wiley & Sons, Ltd.  相似文献   

Origins of compositional heterogeneity in olivine-hosted melt inclusions from the Baffin Island picrites   总被引：1，自引：1，他引：0  

Gregory?M.?YaxleyEmail author  Vadim?S.?Kamenetsky  Maya?Kamenetsky  Marc?D.?Norman  Don?Francis 《Contributions to Mineralogy and Petrology》2004,148(4):426-442

The Baffin Island picrites are highly magnesian (22 wt% MgO) olivine tholeiites, erupted through felsic continental crust. Plots of most major and minor element oxides against MgO for the lavas define very tight trends consistent with modification of melts parental to the erupted suite by olivine fractionation or accumulation. However, melt inclusions trapped in primitive olivine phenocrysts in these lavas have much more diverse compositions. After correction for post-entrapment modification, the inclusions are systematically slightly lower in Al₂O₃, and significantly higher in SiO₂, K₂O and P₂O₅ than the lavas fractionation trends. CaO, Na₂O and TiO₂ contents lie within the lavas fractionation trends. Similarly, most inclusions are higher in Sr/Nd, K/Nb, Rb/Ba, Rb/Sr, U/Nb and Ba/Th than the lavas. These characteristics resulted from up to 15% contamination of evolving picritic-basaltic liquids by locally-derived, broadly granitic partial melts of the quartz + feldspar-rich crust through which the picrites erupted. Contamination was minor in the bulk lavas (<1%), suggesting that the inclusions compositions partly reflect a link between wall rock reaction and precipitation of liquidus olivine. Rapid crystallisation of liquidus olivine from the picrites, along with melting of felsic crustal wall rocks of magma chambers or conduits, were likely during emplacement of hot picritic magmas into cooler felsic crust. Inclusion compositions may thus reflect mixing trends or may be constrained to phase boundaries between olivine and a phase being resorbed, for example, an olivine-plagioclase cotectic. The extent of contamination was probably a complex function of diffusion rates of components in the magmas, and phenocryst growth rates and proximity to wall rock. These results bear on the common observation that melt inclusions compositions are frequently more heterogeneous than those of the lavas that host them.  相似文献   

Hydroacoustic contributions to understanding the December 26th 2004 great Sumatra–Andaman Earthquake     

Maya Tolstoy  DelWayne R. Bohnenstiehl 《Surveys in Geophysics》2006,27(6):633-646

Within the era of modern digital-recording, the December 26th 2004 Sumatra–Andaman Earthquake represents an event of unprecedented scale. Hydroacoustic observations have made significant contributions toward our understanding of this great rupture and serve to reiterate the potential use of tertiary (T) waves as a tool in tsunami warning. Small-aperture arrays of hydrophones operated by the International Monitoring System (IMS) recorded the seismically generated, water-borne T-wave within the Indian Ocean. Due to the velocity structure of the oceanic water column, T-wave propagation is both slower and more efficient than radiation within the solid earth. This results in a relatively large amplitude signal that arrives within a time window distinct from the more complex and overlapping pattern of solid earth seismic phases. Hydroacoustic analysis has constrained the rupture length of the fault to be ~1,200 km and the duration on the order of 8 min, with 2–3 phases exhibiting progressively decreasing rupture velocity. These data also indicate that aftershock rates in the first hours following the mainshock correlate with spatial variability in the sourced T-wave amplitude, with far fewer events along the northern section of the main rupture. Although IMS stations telemeter data in near real time, data access for scientists was restricted due to the provisions of the Comprehensive Test Ban Treaty. The swift dissemination of data will be critical in using hydroacoustic methods to assess the magnitude and tsunamigenic potential of future events.  相似文献   

Partitioning of lanthanides and Y between immiscible silicate and fluoride melts, fluorite and cryolite and the origin of the lanthanide tetrad effect in igneous rocks   总被引：2，自引：0，他引：2  

Ilya V. Veksler  Alexander M. Dorfman  Maya Kamenetsky  Donald B. Dingwell 《Geochimica et cosmochimica acta》2005,69(11):2847-2860

Some F-rich granitic rocks show anomalous, nonchondritic ratios of Y/Ho, extreme negative Eu anomalies, and unusual, discontinuous, segmented chondrite-normalised plots of rare earth elements (REE). The effects of F-rich fluids have been proposed as one of the explanations for the geochemical anomalies in the evolved granitic systems, as the stability of nonsilicate complexes of individual rare earths may affect the fluid-melt element partitioning. The lanthanide tetrad effect, related to different configurations of 4f-electron subshells of the lanthanide elements, is one of the factors affecting such complexing behaviour. We present the first experimental demonstration of the decoupling of Y and Ho, and the tetrad effect in the partitioning of rare earths between immiscible silicate and fluoride melts. Two types of experiments were performed: dry runs at atmospheric pressure in a high-temperature centrifuge at 1100 to 1200°C, and experiments with the addition of H₂O at 700 to 800°C and 100 MPa in rapid-quench cold-seal pressure vessels. Run products were analysed by electron microprobe (major components), solution-based inductively coupled plasma mass spectrometry (ICP-MS) (REE in the centrifuged runs), and laser ablation ICP-MS (REE and Li in the products of rapid-quench runs). All the dry centrifuge runs were performed at super-liquidus, two-phase conditions. In the experiments with water-bearing mixtures, minor amounts of aqueous vapour were present in addition to the melts. We found that lanthanides and Y concentrated strongly in the fluoride liquids, with two-melt partition coefficients reaching values as high as 100-220 in water-bearing compositions. In all the experimental samples, two-melt partition coefficients of lanthanides show subtle periodicity consistent with the tetrad effect, and the partition coefficient of Y is greater than that of Ho. One of the mixtures also produced abundant fluorite (CaF₂) and cryolite (Na₃AlF₆) crystals, which enabled us to study fluorite-melt and cryolite-melt REE partitioning. REE concentrations in fluorite are high and comparable to those in the fluoride melt. However, fluorite-melt partition coefficients appear to depend mostly on ionic radii and show neither significant tetrad anomalies, nor differences in Y and Ho partitioning. In contrast, REE concentrations in cryolite are low (∼5-10 times lower than in the silicate melt), and cryolite-melt REE partitioning shows very strong tetrad and Y-Ho anomalies. Our results imply that Y-Ho and lanthanide tetrad anomalies are likely to be caused mainly by aluminofluoride complexes, and the tetrad REE patterns in natural igneous rocks can result from fractionation of F-rich magmatic fluids.  相似文献   

An inversion scheme to model subsurface fracture systems using shear wave splitting polarization and delay time observations simultaneously   总被引：1，自引：0，他引：1  

Ming Yang  Maya Elkibbi  José A. Rial 《Geophysical Journal International》2005,160(3):939-947

  相似文献   

The Geysers geothermal field: results from shear-wave splitting analysis in a fractured reservoir     

Maya Elkibbi  J. A. Rial 《Geophysical Journal International》2005,162(3):1024-1035

  相似文献   

Transtensional fault-termination basins: an important basin type illustrated by the Pliocene San Jose Island basin and related basins in the southern Gulf of California, Mexico     

Paul J. Umhoefer  Tobias Schwennicke†  Maya T. Del Margo  Gabriela Ruiz-Geraldo†  James C. Ingle Jr.  ‡  William McIntosh§ 《Basin Research》2007,19(2):297-322

Transtensional basins are sparsely described in the literature compared with other basin types. The oblique‐divergent plate boundary in the southern Gulf of California has many transtensional basins: we have studied those on San Jose island and two other transtensional basins in the region. One major type of transtensional basin common in the southern Gulf of California region is a fault‐termination basin formed where normal faults splay off of strike‐slip faults. These basins suggest a model for transtensional fault‐termination basins that includes traits that show a hybrid nature between classic rift and strike‐slip (pull‐apart) basins. The traits include combinations of oblique, strike‐slip and normal faults with common steps and bends, buttress unconformities between the fault steps and beyond the ends of faults, a common facies pattern of terrestrial strata changing upward and away from the faults into marine strata, small fault blocks within the basin that result in complex lateral facies relations, common Gilbert deltas, dramatic termination of the margin of the basin by means of fault reorganization and boundary faults dying and an overall short basin history (few million years). Similar transtensional fault‐termination basins are present in Death Valley and other parts of the Eastern California shear zone of the western United States, northern Aegean Sea and along ancient strike‐slip faults.  相似文献