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41.
夏季青藏高原加热和北半球环流年际变化的相关分析 总被引:16,自引:5,他引:16
利用 195 8~ 1997年NCEP/NCAR再分析数据集中加热率和环流资料 ,采用相关分析和对比分析相结合的方法 ,诊断和分析了夏季青藏高原的非绝热加热与北半球环流系统的年际变化的联系。分析结果表明 :夏季青藏高原的加热强 (弱 )的年份 ,高原及邻近地区的上升运动、下层辐合及上层辐散均增强 (减弱 ) ,使高原加热对周边地区低层暖湿空气的抽吸效应和对高层大气向周边地区的排放作用加强 (减弱 )。从而影响着高原和周边地区的环流以及亚洲季风区大尺度环流系统。而且高原的加热强迫能够激发产生一支沿亚欧大陆东部海岸向东北方向传播的Rossby波列 ,其频散效应可影响到更远的东太平洋以至北美地区的大气环流 相似文献
42.
Near Wall Flow over Urban-like Roughness 总被引:3,自引:35,他引:3
In this study, comprehensive measurements over a number of urban-type surfaces with the same area density of 25% have been performed in a wind tunnel. The experiments were conducted at a free stream velocity of 10 m s-1 and the main instrumentation was 120 ° x-wire anemometry, but measurement accuracy was checked using laser Doppler anemometry.The results haveconfirmed the strong three-dimensionalityof the turbulent flow inthe roughness sublayer and the depths of the inertial sublayer (log-law region) and roughness sublayer for each surface have been determined. Spatial averaging has been used to remove the variability of the flow in the roughness sublayer due to individual obstacles and it is shown that the spatially averaged mean velocity in the inertial sublayer and roughness sublayer can,together, be described by a single log-law with a mean zero-plane displacement and roughness length for the surface, provided that the proper surface stress is known. The spatially averaged shear stresses in the inertial sublayer and roughness sublayer are compared with the surface stress deduced from form drag measurements on the roughness elements themselves.The dispersive stress arising from the spatial inhomogeneity in the mean flow profiles was deduced from the data and is shown to be negligible compared with the usual Reynolds stresses in the roughness sublayer. Comparisons have been made between a homogeneous (regular element array) surface and one consisting of random height elements of the same total volume. Although the upper limits of the inertial sublayer for both surfaces were almost identical at equivalent fetch, the roughness sublayer was much thicker for the random surface than for the uniform surface, the friction velocity and the roughness length were significantly larger and the `roughness efficiency' was greater. It is argued that the inertial sublayer may not exist at all in some of the more extreme rough urban areas. These results will provide fundamental information for modelling urban air quality and forecasting urban wind climates. 相似文献
43.
The chemical composition of fogwater has been studied in the city of Strasbourg (France) from 1990 to 1999. During these years, fogwater samples have been collected and analysed for major ions and trace metals. This paper reports on the analysis of the collected dataset. The analysis revealed a significant decrease in acidity of approximately one pH unit over the course of the study. This decrease in acidity appears to be linked to a decrease in SO2(g) and the resulting SO42−. Trace metal concentrations have also strongly decreased over the 10-year period. Pb concentrations, following the elimination of leaded gasoline, decreased by more than one order of magnitude. 相似文献
44.
在对河南油田双河矿区油田污水进行全分析的基础上,研究了污水中Fe^2 ,S^2-,溶解氧(DO)及污水的pH值对有机交联体系聚丙烯酰胺(HPAM)-酚醛胶态分散凝胶(CDG)成胶性能的影响。研究结果表明,Fe^2 ,S^2-,DO及污水的pH值对HPAM-酚醛体系的成胶性能都有影响当ρ(Fe^2 )=1.6mg/L,ρ(S^2-)=0.1mg/L,ρ(DO)=1.6mg/L,HPAM-酚醛体系就不能成胶;随着污水pH值的增大,CDG强度变弱。 相似文献
45.
Identifying and quantifying urban recharge: a review 总被引:12,自引:1,他引:12
David N. Lerner 《Hydrogeology Journal》2002,10(1):143-152
The sources of and pathways for groundwater recharge in urban areas are more numerous and complex than in rural environments.
Buildings, roads, and other surface infrastructure combine with man-made drainage networks to change the pathways for precipitation.
Some direct recharge is lost, but additional recharge can occur from storm drainage systems. Large amounts of water are imported
into most cities for supply, distributed through underground pipes, and collected again in sewers or septic tanks. The leaks
from these pipe networks often provide substantial recharge. Sources of recharge in urban areas are identified through piezometry,
chemical signatures, and water balances. All three approaches have problems. Recharge is quantified either by individual components
(direct recharge, water-mains leakage, septic tanks, etc.) or holistically. Working with individual components requires large
amounts of data, much of which is uncertain and is likely to lead to large uncertainties in the final result. Recommended
holistic approaches include the use of groundwater modelling and solute balances, where various types of data are integrated.
Urban recharge remains an under-researched topic, with few high-quality case studies reported in the literature.
Electronic Publication 相似文献
46.
47.
Comparison of Seismic Dispersion and Attenuation Models 总被引:2,自引:0,他引:2
The frequency-dependent attenuation of seismic waves causes decreased resolution of seismic images with depth, and the difference in transmission losses induces amplitude variations with offset. Transmission losses may occur due to friction or fluid movement, or may result from scattering in thin-layer. Whatever the physical mechanism, they can often be conveniently described using an empirical formulation wherein the elastic moduli and propagation velocity are complex functions of frequency.We have compiled and compared algebraically and numerically eight different models involving complex velocity: the Kolsky-Futterman model, the power-law model, Kjartansson's model, Müller's model, Azimi's second and third model, the Cole-Cole model, and the standard linear-solid model.For two different parameter sets, the attenuation and phase velocity are computed in the seismic frequency band, and the plane-wave propagation of a Ricker wavelet for the other models is compared with that for the Kolsky-Futterman model. The first parameter set consists of parameters for each of the models calculated from expressions given in the appendix. These expressions make the different models behave similarly to the KF model. The second parameter set consists of model parameters that are numerically adapted to the KF model.By selecting proper parameters, all models, except the standard linear-solid model, show behavior similar to that of the Kolsky-Futterman model. The SLS model behaves differently from the other models as the frequency goes to zero or infinity. Broadband measurement data is needed to select a specific model for a given seismic experiment. 相似文献
48.
49.
广州城市空间形态扩展中土地供应动力机制的作用 总被引:11,自引:0,他引:11
近 10年来呈剧烈变动状态的广州城市空间形态 ,刻烙着城市有机体内外部矛盾碰撞摩擦的痕迹 ,其中包含着权力行为力在空间的冲突过程。文中拟就从人文主义方法论的角度 ,以土地供应为中介媒体 ,研究分析它的供应机制对近 10年广州城市空间形态生长的影响 ,映视土地供应背后权力行为力对城市空间形态扩展影响的一般规律 ,以引导城市空间的健康发展 相似文献
50.
城市生态环境质量是影响城市景观和居民身心健康的重要因素,环境质量分区是进行生态环境评价的基础性工作。在以往生态环境质量评价中,通常采用单一的环境污染指标,难以全面综合的反应生态环境质量状况。植被的面貌是一定时期内大气、土壤、水分、人类活动综合作用的结果。由于树木有生命而又不能移动,它的健康状态是一定时期因素内,综合地反映其生活环境条件的最好尺度。借鉴国外环境诊断的研究方法,提出“树木活力度”,即树木的枝、叶、梢、树形等各个部位的生长状况和健康程度这一新的综合生态指标,并结合实际,以吉林市为例,对运用这一指标进行城市生态环境质量评价的方法、原理、问题等进行了初步探讨。指出运用树木活力度进行城市生态环境质量分区,具有迅速目测、计算简便,快速经济的特点,是当前较为流行的一种景观诊断的简便易行的方法。 相似文献