The use of scale recursive estimation for short term quantitative precipitation forecast     

D. Bocchiola  R. Rosso 《Physics and Chemistry of the Earth》2006,31(18):1228-1239

Scale recursive estimation (SRE) is adopted for short term quantitative precipitation forecast (QPF). The precipitation field is modelled using a lognormal random cascade, well suited to properly represent the scaling properties of rainfall fields. To estimate the random cascade parameters, scale recursive maximum likelihood estimation (MLE) is carried out by the iterative expectation maximization (EM) algorithm. To illustrate the potentiality of the SRE, forecast of a synthetically generated rainfall time series is shown. Adaptive estimation of the process parameters is carried out and precipitation forecasts are issued. The forecasts from the SRE are compared with those from standard ARMA models, showing a good performance. The SRE is then adopted for forecasting of an observed half hourly precipitation series for a two day storm event in northern Italy. The SRE provides good performance and it can therefore be adopted as a tool for short term QPF.  相似文献   

Seasonal changes in ground‐penetrating radar signature observed at a polythermal glacier,Bylot Island,Canada     

T. D. L. Irvine‐Fynn  B. J. Moorman  J. L. M. Williams  F. S. A. Walter 《地球表面变化过程与地形》2006,31(7):892-909

In recent years, ground‐penetrating radar (GPR) has been increasingly used for characterization of subglacial and englacial environments at polythermal glaciers. The geophysical method is able to exploit the dielectric difference between water, air, sediment and ice, allowing delineation of subsurface hydrological, thermal and structural conditions. More recent GPR research has endeavoured to examine temporal change in glaciers, in particular the distribution of the cold ice zone at polythermal glaciers. However, the exact nature of temporal change that can be identified using GPR has not been fully examined. This research presents the results of three GPR surveys conducted over the course of a summer ablation season at a polythermal glacier in the Canadian Arctic. A total of approximately 30 km of GPR profiles were collected in 2002 repeatedly covering the lower 2 km of Stagnation Glacier, Bylot Island (72°58′ N 78°22′ W). Comparison between profiles indicated changes in the radar signature, including increased noise, appearance and disappearance of englacial reflections, and signal attenuation in the latter survey. Further, an area of chaotic returns in up‐glacier locations, which was interpreted to be a wet temperate ice zone, showed marked recession over the course of the ablation season. Combining all the temporal changes that were detected by GPR, results indicate that a polythermal glacier may exhibit strongly seasonal changes in hydrological and thermal characteristics throughout the ice body, including the drainage of 17 000 m³ of temporarily stored intra‐glacial meltwater. It is also proposed that the liquid water content in the temperate ice zone of polythermal glaciers can be described as a fraction of a specific retention capacity. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Identification of critical ground motions for seismic performance assessment of structures   总被引：1，自引：0，他引：1  

Rajesh P. Dhakal  John B. Mander  Naoto Mashiko 《地震工程与结构动力学》2006,35(8):989-1008

A method is established to identify critical earthquake ground motions that are to be used in physical testing or subsequent advanced computational studies to enable seismic performance to be assessed. The ground motion identification procedure consists of: choosing a suitable suite of ground motions and an appropriate intensity measure; selecting a computational tool and modelling the structure accordingly; performing Incremental Dynamic Analysis on a non‐linear model of the structure; interpreting these results into 50th (median) and 90th percentile performance bounds; and identifying the critical ground motions that are close to these defining probabilistic curves at ground motion intensities corresponding to the design basis earthquake and the maximum considered earthquake. An illustrative example of the procedure is given for a reinforced concrete highway bridge pier designed to New Zealand specifications. Pseudodynamic tests and finite element based time history analyses are performed on the pier using three earthquake ground motions identified as: (i) a Design Basis Earthquake (10% probability in 50 years) with 90 percent confidence of non‐exceedance; (ii) a Maximum Considered Event (2% probability in 50 years) representing a median response; and (iii) a Maximum Considered Event representing 90 percent confidence of non‐exceedance. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Flexural deformation capacity of rectangular RC columns determined by the CAE method     

Iztok Peru&#x;  Karmen Poljan&#x;ek  Peter Fajfar 《地震工程与结构动力学》2006,35(12):1453-1470

A non‐parametric empirical approach, called the conditional average estimator (CAE) method, has been implemented for the estimation of the flexural deformation capacity of reinforced concrete rectangular columns expressed in terms of the ultimate (‘near collapse’) drift. Two databases (PEER and Fardis), which represent subsets of the original databases, were used. Four input parameters were employed in the basic model: axial load index, index related to confinement, shear span index, and concrete compressive strength. The results of analyses suggest that, in general, ultimate drift decreases with increasing axial load index, and increases with better confinement. An increase in the shear span‐to‐depth ratio has a beneficial effect until a turning point is reached. After that the opposite trend can be observed, i.e. a decrease in the ultimate drift with further increasing of the shear span‐to‐depth ratio. No clear trend is observed in the case of concrete compressive strength. The predictions, obtained by using the Fardis database are in general somewhat larger than the predictions from the PEER database, due to the difference in the definition of ultimate drift. The scatter of results is large. The local coefficient of variation, which is a measure for dispersion, amounts to about 0.2–0.5. The ultimate drifts obtained by using the two databases, were compared with the values predicted by the Eurocode 8 empirical formula. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

我国1978～2004年生态足迹需求与供给动态分析   总被引：4，自引：1，他引：4  

钟晓青  赵永亮  钟山  司寰 《武汉大学学报(信息科学版)》2006,31(11):1022-1026

基于生态足迹理论，用实证方法进行了我国可持续发展的定量测算与分析。在静点测算基础上，对我国20多年来的生态足迹供给与需求进行了动态测算与分析。通过Eviews软件分析了生态足迹与GDP、POP（人口）的线性关系。利用分析结果和变量之间的估计方程可以判断我国可持续发展状况，并预测未来走势。  相似文献   

青海湖地区天然牧草对水分条件反应特性分析   总被引：1，自引：0，他引：1  

严应存  高贵生  严进瑞 《气象》2006,32(8):107-112

利用青海省铁卜加牧业气象试验站1987-1996年的气象和牧草资料，研究了降水、土壤湿度与蒸发量等水分条件对青海湖地区铁卜加草原5种优势种天然牧草生长高度及产量形成的影响。结果表明：环湖地区山地草原草场中紫花针茅Stipa purpurea、冷地早熟禾Poa crymophila、干生苔草Carex aridula、猪毛蒿Artemisia scoparia、天山赖草Leymus tianschanicum、杂草产量比为8：15：15：16：18：28。5种天然牧草的生长高度和产量对水分条件表现出不同的反应，天山赖草最耐旱；干生苔草次之；猪毛蒿和紫花针茅的抗旱性相当；冷地早熟禾对水分条件的反应最为敏感，得出了大部分牧草产量形成需水临界期在6月份的结论。这对环青海湖地区草地增水抗旱工作的时间安排具有指导作用。  相似文献   

岩土参数相关性的地基承载力模糊可靠性分析     

付兵先  唐飞  赵峰 《岩土工程技术》2006,20(1):45-47

地基的失效可视为模糊事件。影响地基承载力因素表现出空间变异性。根据随机场理论描述土性参数的空间变异性,考虑土性参数的自相关性及其互相关性,得出参数间的相关性在可靠性分析中不可忽视的结论。  相似文献   

碎石桩复合地基设计方法的探讨   总被引：3，自引：0，他引：3  

李燕杰  牛志民 《岩土工程技术》2006,20(1):48-50,F0003

通过对碎石桩复合地基承载力和抗震液化设计的对比和分析,提出了以承载力和抗震液化相互综合考虑的设计方法。  相似文献   

宝鸡市城区地下水资源调控探讨     

郑磊  ZHENG Lei 《地下水》2006,28(4):4-6

地下水资源是宝鸡市市区的主要供水水源,由于超采致使水位逐年急剧下降,水质受到不同程度污染.本文通过对城市地下水资源承载能力进行分析,提出了保护城市地下水资源,实现可持续利用的调控措施.  相似文献   

非均质地基承载力及破坏模式的FLAC数值分析   总被引：3，自引：0，他引：3  

赵少飞  栾茂田  范庆来  吕爱钟  袁凡凡 《岩土力学》2006,27(11):1909-1914

利用基于Lagrangian显式差分的FLAC算法，通过数值计算，对黏结力随深度线性增长的非均质地基上条形基础和圆形基础的极限承载力及地基破坏模式进行了对比计算与系统分析。研究表明：（1）随着地基黏结力沿深度非均匀变化系数的增大，地基的破坏范围逐渐集中在地基表层和基础两侧：（2）即使地基的非均质程度较小，当将非均质地基近似地按均质地基考虑时，由此所估算的承载力可能过于保守；（3）地基承载力系数随黏结力沿深度非均匀变化系数的增大而非线性地增大。与数值解相比，skempton与Peck等近似公式均可能高估了非均质地基承载力。  相似文献