Pervasive Web Mapping,Geoprocessing and Services     

Suzana Dragićević  Songnian Li  Maria Brovelli  Bert Veenendaal 《Transactions in GIS》2011,15(2):125-127

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Evaluation of the Diurnal Cycle in the Atmospheric Boundary Layer Over Land as Represented by a Variety of Single-Column Models: The Second GABLS Experiment   总被引：3，自引：3，他引：0  

G. Svensson  A. A. M. Holtslag  V. Kumar  T. Mauritsen  G. J. Steeneveld  W. M. Angevine  E. Bazile  A. Beljaars  E. I. F. de Bruijn  A. Cheng  L. Conangla  J. Cuxart  M. Ek  M. J. Falk  F. Freedman  H. Kitagawa  V. E. Larson  A. Lock  J. Mailhot  V. Masson  S. Park  J. Pleim  S. S?derberg  W. Weng  M. Zampieri 《Boundary-Layer Meteorology》2011,140(2):177-206

We present the main results from the second model intercomparison within the GEWEX (Global Energy and Water cycle EXperiment) Atmospheric Boundary Layer Study (GABLS). The target is to examine the diurnal cycle over land in today??s numerical weather prediction and climate models for operational and research purposes. The set-up of the case is based on observations taken during the Cooperative Atmosphere-Surface Exchange Study-1999 (CASES-99), which was held in Kansas, USA in the early autumn with a strong diurnal cycle with no clouds present. The models are forced with a constant geostrophic wind, prescribed surface temperature and large-scale divergence. Results from 30 different model simulations and one large-eddy simulation (LES) are analyzed and compared with observations. Even though the surface temperature is prescribed, the models give variable near-surface air temperatures. This, in turn, gives rise to differences in low-level stability affecting the turbulence and the turbulent heat fluxes. The increase in modelled upward sensible heat flux during the morning transition is typically too weak and the growth of the convective boundary layer before noon is too slow. This is related to weak modelled near-surface winds during the morning hours. The agreement between the models, the LES and observations is the best during the late afternoon. From this intercomparison study, we find that modelling the diurnal cycle is still a big challenge. For the convective part of the diurnal cycle, some of the first-order schemes perform somewhat better while the turbulent kinetic energy (TKE) schemes tend to be slightly better during nighttime conditions. Finer vertical resolution tends to improve results to some extent, but is certainly not the solution to all the deficiencies identified.  相似文献   

Report on the 4th International Meeting of the IUGS Lower Cretaceous Ammonite Working Group, the “Kilian Group” (Dijon, France, 30th August 2010)     

Stéphane Reboulet  Peter F. Rawson  Josep A. Moreno-Bedmar  Maria B. Aguirre-Urreta  Ricardo Barragán  Yuri Bogomolov  Miguel Company  Celestina González-Arreola  Vyara Idakieva Stoyanova  Alexander Lukeneder  Bertrand Matrion  Vasily Mitta  Hasina Randrianaly  Zdenek Vaši?ek  Evgenij J. Baraboshkin  Didier Bert  Stéphane Bersac  Tamara N. Bogdanova  Luc G. Bulot  Jean-Louis Latil  Irina A. Mikhailova  Pierre Ropolo  Ottilia Szives 《Cretaceous Research》2011,32(6):786-793

The 4th Kilian Group meeting (Dijon, France, 30th August 2010) focused on the Aptian and Albian Stages. For the Aptian, a two-fold division of the stage was adopted for the Mediterranean area with a boundary between the Dufrenoyia furcata and Epicheloniceras martini Zones. The main changes to the zonal scheme concern the Lower Aptian with: the introduction of a Deshayesites luppovi Subzone in the upper part of the Deshayesites oglanlensis Zone; the replacement of Deshayesites weissi by Deshayesites forbesi as new index-species of the second interval zone; the introduction of a Roloboceras hambrovi Subzone in the upper part of the D. forbesi Zone; and the subdivision of the D. furcata Zone into the D. furcata and Dufrenoyia dufrenoyi Subzones. For the Albian, the upper part of the Douvilleiceras mammillatum Zone (Lower Albian) is now characterized by a Lyelliceras pseudolyelli Subzone. The main amendments concern the Upper Albian. The base of this substage is defined by the base of the Dipoloceras cristatum Zone. Above it, the Upper Albian zonal scheme comprises in stratigraphic order the Mortoniceras pricei, Mortoniceras inflatum, Mortoniceras fallax, Mortoniceras rostratum, Mortoniceras perinflatum and Arrhaphoceras briacensis Zones.  相似文献   

Reply to comments on ‘scaling the atmospheric boundary layer’     

A. A. M. Holtslag  F. T. M. Nieuwstadt 《Boundary-Layer Meteorology》1987,38(4):415-416

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Environmental factors controlling spatial variation in sediment yield in a central Andean mountain area     

Armando Molina  Gerard Govers  Jean Poesen  Hendrik Van Hemelryck  Bert De Bivre  Veerle Vanacker 《Geomorphology》2008,98(3-4):176

A large spatial variability in sediment yield was observed from small streams in the Ecuadorian Andes. The objective of this study was to analyze the environmental factors controlling these variations in sediment yield in the Paute basin, Ecuador. Sediment yield data were calculated based on sediment volumes accumulated behind checkdams for 37 small catchments. Mean annual specific sediment yield (SSY) shows a large spatial variability and ranges between 26 and 15,100 Mg km^− 2 year^− 1. Mean vegetation cover (C, fraction) in the catchment, i.e. the plant cover at or near the surface, exerts a first order control on sediment yield. The fractional vegetation cover alone explains 57% of the observed variance in ln(SSY). The negative exponential relation (SSY = a × e^{−b C}) which was found between vegetation cover and sediment yield at the catchment scale (10³–10⁹ m²), is very similar to the equations derived from splash, interrill and rill erosion experiments at the plot scale (1–10³ m²). This affirms the general character of an exponential decrease of sediment yield with increasing vegetation cover at a wide range of spatial scales, provided the distribution of cover can be considered to be essentially random. Lithology also significantly affects the sediment yield, and explains an additional 23% of the observed variance in ln(SSY). Based on these two catchment parameters, a multiple regression model was built. This empirical regression model already explains more than 75% of the total variance in the mean annual sediment yield. These results highlight the large potential of revegetation programs for controlling sediment yield. They show that a slight increase in the overall fractional vegetation cover of degraded land is likely to have a large effect on sediment production and delivery. Moreover, they point to the importance of detailed surface vegetation data for predicting and modeling sediment production rates.  相似文献   

Training the rivers and exploring the coasts. Knowledge evolution in the Netherlands in two engineering fields between 1800 and 1940     

Bert Toussaint 《Physics and Chemistry of the Earth》2009,34(3):132-141

In this paper, the author wants to explore the knowledge development in two crucial fields, river management and coast management in the 19th century and first decades of the 20th century. Were there similar characteristics in this development? Which types of knowledge can be distinguished? Who were the principal actors in these processes? Did the knowledge evolution have a Dutch stamp or a rather international flavour?To structure the analysis, the author uses the concept of technology regime, a set of technical rules which shapes the know-how of engineers, their design rules and research processes. The analysis shows that the knowledge development of river management and coastal management followed different evolution paths between 1800 and 1940. In the field of river management, a substantial amount of mathematical and physical theories had been gradually developed since the end of the 17th century. After 1850, the regularization approach met gradually a widespread support. Empirical data, design rules, theoretical knowledge and engineering pivoted around the regularization approach, and a technology regime around this approach emerged. The regularization regime further developed in the 20th century, and handbooks were increasingly shaped by mathematical and physical reasoning and formulas. On the other hand, coastal management was until the 1880s a rather marginal activity. Coastal engineering was an extremely complex and multidimensional field of knowledge which no engineer was able to grasp.The foundation of a Dutch weather institute was a first important step towards a more theoretical approach. The Zuiderzee works (starting in 1925) gave probably the most important stimuli to scientific coastal research. It was also a main factor in setting up scientific institutes by Rijkswaterstaat. So from the 1920s, Rijkswaterstaat became a major producer of scientific knowledge, not only in tidal modelling but also in coastal research. Due to a multidisciplinary knowledge network, coastal research transformed from a marginal to a first-rank scientific field, and this transformation enabled Rijkswaterstaat to set a much higher level of ambition in coastal management. The 1953 flood and the Deltaworks marked a new era. New design rules for sea dykes and river levees, based on a revolutionary statistical risk approach were determined, and design rules for the Deltaworks estuary closures were developed, being enabled by the development of hydraulic research.  相似文献   

Impacts of land use on the hydrological response of tropical Andean catchments          下载免费PDF全文

Boris F. Ochoa‐Tocachi  Wouter Buytaert  Bert De Bièvre  Rolando Célleri  Patricio Crespo  Marcos Villacís  Carlos A. Llerena  Luis Acosta  Mauricio Villazón  Mario Guallpa  Junior Gil‐Ríos  Paola Fuentes  Dimas Olaya  Paúl Viñas  Gerver Rojas  Sandro Arias 《水文研究》2016,30(22):4074-4089

Changes in land use and land cover are major drivers of hydrological alteration in the tropical Andes. However, quantifying their impacts is fraught with difficulties because of the extreme diversity in meteorological boundary conditions, which contrasts strongly with the lack of knowledge about local hydrological processes. Although local studies have reduced data scarcity in certain regions, the complexity of the tropical Andes poses a big challenge to regional hydrological prediction. This study analyses data generated from a participatory monitoring network of 25 headwater catchments covering three of the major Andean biomes (páramo, jalca and puna) and links their hydrological responses to main types of human interventions (cultivation, afforestation and grazing). A paired catchment setup was implemented to evaluate the impacts of change using a ‘trading space‐for‐time’ approach. Catchments were selected based on regional representativeness and contrasting land use types. Precipitation and discharge have been monitored and analysed at high temporal resolution for a time period between 1 and 5 years. The observed catchment responses clearly reflect the extraordinarily wide spectrum of hydrological processes of the tropical Andes. They range from perennially humid páramos in Ecuador and northern Peru with extremely large specific discharge and baseflows, to highly seasonal, flashy catchments in the drier punas of southern Peru and Bolivia. The impacts of land use are similarly diverse and their magnitudes are a function of catchment properties, original and replacement vegetation and management type. Cultivation and afforestation consistently affect the entire range of discharges, particularly low flows. The impacts of grazing are more variable but have the largest effect on the catchment hydrological regulation. Overall, anthropogenic interventions result in increased streamflow variability and significant reductions in catchment regulation capacity and water yield, irrespective of the hydrological properties of the original biome. Copyright © 2016 The Authors. Hydrological Processes. Published by John Wiley & Sons Ltd.  相似文献   

Organic Contaminants in Portland Cements Used in Monitoring Well Construction     

Bert Smith  Donald Siegel  Charles Neslund  Charles Carter 《Ground Water Monitoring & Remediation》2014,34(4):102-111

We report the results of two independent laboratory investigations to evaluate total and leachable concentrations of glycols, glycol ethers, phenol, and other compounds in representative Type I and Type I/II Portland cement products that United States Environmental Protection Agency (EPA), The American Society of Testing and Materials (ASTM) and others recommend as annular sealants in monitoring well completions. Water well drillers also use these cements in their well completions. The EPA has included some of these compounds for analysis in their National Hydraulic Fracturing Study to evaluate the effects of hydraulic fracturing on ground‐ and surface water resources. During any contaminant investigation, materials used in monitoring or water well drilling, completion, development, and sampling must be free of the chemicals being targeted by the regulatory agency. Three of five bulk cement products we tested contained part per million (ppm) (mg/kg) concentrations of diethylene glycol, ethylene glycol, tetraethylene glycol, and triethylene glycol; chemicals added as grinding aids during manufacture. Some cements also contained ppb (µg/kg) concentrations of benzoic acid, phenols, propylene glycol, and 2‐butoxyethanol. Leaching of cured cement samples in water produced ppm (mg/L) concentrations of glycols in the supernatant. These results show that cured cements in monitoring or water wells can contaminate groundwater samples with glycols and phenol. Our findings should help prevent future sample bias and false positives when testing for glycol compounds and phenol in groundwater samples from monitoring or water wells and highlight the need to test materials or products used in monitoring or water well drilling, completions, development, and sampling to avoid false positives when sampling and analyzing for less common analytical constituents.  相似文献   

Sensitivity of the Eastern Mediterranean geomorphic system towards environmental change during the Late Holocene: a chronological perspective     

Bert Dusar  Gert Verstraeten  Koen D'haen  Johan Bakker  Eva Kaptijn  Marc Waelkens 《第四纪科学杂志》2012,27(4):371-382

Alluvial and colluvial sediment deposition provide a vital record of environmental change during the Holocene. Firm chronological control on these archives is necessary to enable us to relate sediment dynamics to human activity and climate variability. In the Eastern Mediterranean, such relationships are hard to establish due to the lack of spatially well‐distributed sediment archives with good chronological control. This scarcity is problematic with respect to regional‐scale reconstructions of the temporal variation of sediment dynamics. Here, we present a radiocarbon database (n = 178) of geomorphological activity collected from multiple distinct sediment archives within the territory of Sagalassos in south‐western Turkey. The data were grouped according to their sedimentary facies for analysis using cumulative probability distributions (CPDs) and sedimentation rate (SR) modelling. Two small‐scale colluvial valleys, where chronological information was abundant, were investigated in more detail. Results show that sedimentation chronology differs between individual, nearby cores, as it depends strongly on the local geomorphic situation. A generalizing approach combining multiple core results yields more widely valid conclusions. High sedimentation rates coincided with the initial major anthropogenic disturbance of the landscape and decreased afterwards, probably due to hillslope soil depletion. CPD and SR analysis indicates that in general colluvial sedimentation rates did not change much from 2000 BC onwards. River floodplain sedimentation, in contrast, increased markedly during the first millennium BC and during recent times, and a significant time lag in enhanced sediment deposition between the upper and lower reaches of the river valleys was observed. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Effects of low-viscous layers and a non-zero obliquity on surface stresses induced by diurnal tides and non-synchronous rotation: The case of Europa     

Hermes M. Jara-Orué  Bert L.A. Vermeersen 《Icarus》2011,215(1):417-438

In this study we present a semi-analytical Maxwell-viscoelastic model of the variable tidal stress field acting on Europa’s surface. In our analysis, we take into account surface stresses induced by the small eccentricity of Europa’s orbit, the non-zero obliquity of Europa’s spin axis - both acting on a diurnal 3.55-days timescale - and the reorientation of the ice shell as a result of non-synchronous rotation (NSR). We assume that Europa’s putative ocean is covered by an ice shell, which we subdivide in a low-viscous and warm lower ice layer (asthenosphere, viscosity 10¹²-10¹⁷ Pa s), and a high-viscous and cold upper ice layer (lithosphere, viscosity 10²¹ Pa s).Viscoelastic relaxation influences surface stresses in two ways: (1) through viscoelastic relaxation in the lithosphere and (2) through the viscoelastic tidal response of Europa’s interior. The amount of relaxation in the lithosphere is proportional to the ratio between the period of the forcing mechanism and the Maxwell time of the high-viscous lithosphere. As a result, this effect is only relevant to surface stresses caused by the slow NSR mechanism. On the other hand, the importance of the viscoelastic response on surface stresses is proportional to the ratio between the relaxation time (τ_j) of a given viscoelastic mode j and the period of the forcing function. On a diurnal timescale the fast relaxation of transient modes related to the low viscosity of the asthenosphere can alter the magnitude and phase shift of the diurnal stress field at Europa’s surface. The effects are largest, up to 20% in magnitude and 7° in phase for ice rigidities lower than 3.487 GPa, when the relaxation time of the aforementioned transient modes approaches the inverse of the average angular rate of Europa’s orbit. On timescales relevant for NSR (>10⁴ years) the magnitude and phase shift of NSR surface stresses can be affected by viscoelastic relaxation of the ocean-ice boundary. This effect, however, becomes only important when the behavior of the lithosphere w.r.t. NSR approaches the fluid limit, i.e. for strong relaxation in the lithosphere. The combination of NSR and diurnal stresses for different amounts of viscoelastic relaxation of NSR stresses in the lithosphere leads to a large variety of global stress fields that can explain the formation of the large diversity of lineament morphologies observed on Europa’s surface. Variation of the amount of relaxation in the lithosphere is likely due to changes in the spin rate of Europa and/or the rheological properties of the surface.In addition, we show that a small obliquity(<1°) can have a considerable effect on Europa’s diurnal stress field. A non-zero obliquity breaks the symmetric distribution of stress patterns with respect to the equator, thereby affecting the magnitude and orientation of the principal stresses at the surface. As expected, increasing the value of Europa’s obliquity leads to larger diurnal stresses at the surface, especially when Europa is located 90° away from the nodes formed by the intersection of its orbital and equatorial planes.  相似文献