The Budget of Turbulent Kinetic Energy in the Urban Roughness Sublayer   总被引：4，自引：4，他引：0  

Andreas Christen  Mathias W. Rotach  Roland Vogt 《Boundary-Layer Meteorology》2009,131(2):193-222

Full-scale observations from two urban sites in Basel, Switzerland were analysed to identify the magnitude of different processes that create, relocate, and dissipate turbulent kinetic energy (TKE) in the urban atmosphere. Two towers equipped with a profile of six ultrasonic anemometers each sampled the flow in the urban roughness sublayer, i.e. from street canyon base up to roughly 2.5 times the mean building height. This observational study suggests a conceptual division of the urban roughness sublayer into three layers: (1) the layer above the highest roofs, where local buoyancy production and local shear production of TKE are counterbalanced by local viscous dissipation rate and scaled turbulence statistics are close to to surface-layer values; (2) the layer around mean building height with a distinct inflexional mean wind profile, a strong shear and wake production of TKE, a more efficient turbulent exchange of momentum, and a notable export of TKE by transport processes; (3) the lower street canyon with imported TKE by transport processes and negligible local production. Averaged integral velocity variances vary significantly with height in the urban roughness sublayer and reflect the driving processes that create or relocate TKE at a particular height. The observed profiles of the terms of the TKE budget and the velocity variances show many similarities to observations within and above vegetation canopies.  相似文献   

Evidence of rainfall variations in Southern Brazil from trace element ratios (Mg/Ca and Sr/Ca) in a Late Pleistocene stalagmite   总被引：1，自引：0，他引：1  

Francisco W. Cruz Jr.  Stephen J. Burns  Ivo Karmann  Mathias Vuille 《Geochimica et cosmochimica acta》2007,71(9):2250-2263

Trace element ratios in the Bt2 stalagmite from Botuverá cave, Southern Brazil, are explored as a proxy for changes in the local rainfall recharge during the last 116 ky. BP Mg/Ca and Sr/Ca ratios, measured with an electron microprobe, are significantly positively correlated with one another throughout the entire record, and vary in a way that is very consistent with variations of δ¹⁸O in the same speleothem during the last glacial period. We suggest that prior calcite precipitation in the vadose zone of the cave system is the main factor affecting the incorporation of Mg and Sr into calcite of the stalagmite. This interpretation is supported by trace element correlation patterns and by results from a hydrochemistry study performed in a cave located in the same region and in a similar environmental setting. Therefore, we conclude that higher (lower) Mg/Ca and Sr/Ca values are associated with lower (higher) levels of recharge into the karstic aquifer, as such conditions lead to an increase (decrease) in the volume of calcite precipitated in the unsaturated zone above the cave during dry (wet) climate periods.Trace element variations point to generally dryer (wetter) conditions during lower (high) phases of summer insolation in the southern hemisphere. These periods coincide with decreased (increased) activity of the South American summer monsoon, as revealed by δ¹⁸O stalagmite records. In addition trace element variations show that rather wet conditions persisted throughout most of the last glacial period from approximately 70 to 17 ky BP. We suggest that during this period the glacial boundary conditions, especially ice volume buildup in the northern hemisphere, played an important role for monsoon rainfall intensification in the region.  相似文献   

Quantitation of Nonextractable Anthropogenic Quantitation of Nonextractable Anthropogenic Sediments after Chemical Degradation     

Jan Schwarzbauer  Mathias Ricking  Ralf Littke 《洁净——土壤、空气、水》2003,31(6):469-481

Four highly contaminated sediment samples obtained from three sampling locations of the Teltow Canal, Berlin, were investigated by quantitation of extractable and nonextractable organic contaminants. The selection of the anthropogenic contaminants (including chlorinated and brominated naphthalenes, 2, 4, 6‐tribromoaniline, phthalates, tri‐n‐butylphosphate, 2, 2, 4‐trimethyl‐1, 3‐pentanediol diisobutyrate, bisphenol A, butylated nitrophenols, 4‐nitrobenzoic acid, galaxolide, and tonalide) based on the results of extended GC‐MS screening analyses applied to the extracts of the sediment samples as well as to the extracts derived from selective chemical degradation procedures. In detail, alkaline hydrolyses, BBr₃‐treatment and RuO₄‐oxidation were applied to the pre‐extracted sediment samples in both a separate and a sequential mode.  相似文献   

The response of the subglacial Lake Vostok, Antarctica, to tidal and atmospheric pressure forcing   总被引：1，自引：0，他引：1  

Anja Wendt  Reinhard Dietrich  Jens Wendt  Mathias Fritsche  Valery Lukin  Alexander Yuskevich  rey Kokhanov  Anton Senatorov  Kazuo Shibuya  Koichiro Doi 《Geophysical Journal International》2005,161(1):41-49

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Historic fluvial development of the Alpine-foreland Tagliamento River, Italy, and consequences for floodplain management     

Mathias Spaliviero   《Geomorphology》2003,52(3-4):317-333

The fluvial geomorphological development of the Tagliamento River and its flooding history is analysed using historical documents and maps, remote-sensed data and hydrological information. The river has been building a complex alluvial fan starting from the middle part of its alluvial course in the Venetia–Friuli alluvial plain. The riverbed is aggrading over its entire braided length. The transition from braiding to meandering near Madrisio has shifted downstream where the river width determined by the dikes becomes narrower, causing major problems. The flood hazard concentrates at those places and zones where flooding occurred during historical times. Prior to the agrarian and industrial revolution, land use was adjusted to the flooding regime of the river. Subsequent land-use pressure led to a confinement of the river by dikes to such an extent that the flood risk in the floodplain downstream of Madrisio has increased consistently, and represents nowadays a major territorial planning issue. The planned retention basins upstream of the middle Tagliamento will alleviate the problem, but not solve it in the medium and long term. Therefore, fluvial corridors in the lower-middle parts (from Pinzano to the sea) have been identified on the basis of the flooding history in relation to fluvial development during historical times. The result should be used for hydraulic simulation studies and land-use planning.  相似文献   

A study of garnets from eclogite and peridotite xenoliths found in kimberlite     

P. C. Rickwood  M. Mathias  J. C. Siebert 《Contributions to Mineralogy and Petrology》1968,19(4):271-301

The chemical compositions of garnets from 58 eclogite, 72 peridotite and 4 pyroxenite xenoliths in kimberlites have been estimated from their unit cell edge length and refractive indices. The samples studied were obtained from 17 kimberlite occurrences and include all those of known source which remain in the famous Williams (1932) collection which is stored at the University of Cape Town. Every suitable sample available to the authors has been examined.A gap in the range of garnet volume percentages occurs in the samples studied between approximately 15 and 30%. Garnet peridotites characteristically have <15% garnet and eclogites >30% garnet. Very rare exceptions occur. Our collection contains no eclogites with olivine and only one with orthopyroxene. All but two of the peridotite-pyroxenite group contain orthopyroxene. The garnets from the peridotites and pyroxenites plot on a pyrope-almandine-uvarovite triangle in a narrow band with a remarkably constant almandine/uvarovite ratio. Garnets from the eclogites are plotted on a pyrope-almandine-grossularite triangle and have a wide spread of compositions. These fall into 4 groups viz. eclogite I, eclogite II, kyanite eclogite and corundum eclogite.The reasons for the differences in garnet chemistry are considered and a tentative evolutionary scheme suggested by partial melting of the garnet peridotite which is assumed to occur in the upper mantle. Recent models of upper mantle composition and the genesis of garnet-bearing xenoliths in kimberlite are briefly and critically examined.S.A. UMP Publication No. 9.  相似文献   

Documentary Evidence on Climate in Sixteenth-Century Europe   总被引：2，自引：0，他引：2  

Christian Pfister  Rudolf Brázdil  Rüdiger Glaser  Mariano Barriendos  Dario Camuffo  Mathias Deutsch  Petr Dobrovolný  Silvia Enzi  Emanuela Guidoboni  Oldřich Kotyza  Stefan Militzer  Lajos Rácz  Fernando S. Rodrigo 《Climatic change》1999,43(1):55-110

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Comments on "Debris-Covered Glaciers in the Sierra Nevada, California, and Their Implications for Snowline Reconstruction," by D. H. Clark, M. M. Clark, and A. R. Gillespie     

Mathias Jacob 《Quaternary Research》1994,42(3)

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Quantitative evaluation of different hydrological modelling approaches in a partly glacierized Swiss watershed     

Jan Magnusson  Daniel Farinotti  Tobias Jonas  Mathias Bavay 《水文研究》2011,25(13):2071-2084

Mountain water resources management often requires hydrological models that need to handle both snow and ice melt. In this study, we compared two different model types for a partly glacierized watershed in central Switzerland: (1) an energy‐balance model primarily designed for snow simulations; and (2) a temperature‐index model developed for glacier simulations. The models were forced with data extrapolated from long‐term measurement records to mimic the typical input data situation for climate change assessments. By using different methods to distribute precipitation, we also assessed how various snow cover patterns influenced the modelled runoff. The energy‐balance model provided accurate discharge estimations during periods dominated by snow melt, but dropped in performance during the glacier ablation season. The glacier melt rates were sensitive to the modelled snow cover patterns and to the parameterization of turbulent heat fluxes. In contrast, the temperature‐index model poorly reproduced snow melt runoff, but provided accurate discharge estimations during the periods dominated by glacier ablation, almost independently of the method used to distribute precipitation. Apparently, the calibration of this model compensated for the inaccurate precipitation input with biased parameters. Our results show that accurate estimates of snow cover patterns are needed either to correctly constrain the melt parameters of the temperature‐index model or to ensure appropriate glacier surface albedos required by the energy‐balance model. Thus, particularly when only distant meteorological stations are available, carefully selected input data and efficient extrapolation methods of meteorological variables improve the reliability of runoff simulations in high alpine watersheds. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Stereotomography assisted by migration of attributes     

Sylvain Nguyen †  Reda Baina  Mathias Alerini ‡  Gilles Lambaré  Vincent Devaux  Mark Noble 《Geophysical Prospecting》2008,56(5):613-625

Depth velocity model building remains a difficult step within the seismic depth imaging sequence. Stereotomography provides an efficient solution to this problem but was limited until now to a picking of seismic data in the prestack time un-migrated domain. We propose here a method for stereotomographic data picking in the depth migrated domain. Picking in the depth migrated domain exhibits the advantage of a better signal-to-noise ratio and of a more regular distribution of picked events in the model, leading to a better constrained tomographic inverse problem. Moreover, any improvement on the velocity model will improve the migrated results, again leading to improved picking. Our strategy for obtaining a stereotomographic dataset from a prestack depth migration is based on migration of attributes (and not on a kinematic demigration approach!). For any locally coherent event in the migrated image, migration of attributes allows one to compute ray parameter attributes corresponding to the specular reflection angle and dip. For application to stereotomography, the necessary attributes are the source/receiver locations, the traveltime and the data slopes. For the data slope, when the migration velocity model is erroneous, some additional corrections have to be applied to the result of migration of the attributes. Applying these corrections, our picking method is theoretically valid whatever the quality of the migration velocity model. We first present the theoretical aspects of the method and then validate it on 2D synthetic and real seismic reflection data sets.  相似文献