地形非均匀性对网格区地面长波辐射通量计算的影响   总被引：2，自引：1，他引：2  

张耀存  丁裕国  陈斌 《气象学报》2006,64(1):39-47

从理论和数值试验两个方面证明地形的非均匀性(如海拔高度)对网格区地面长波辐射通量的计算有重要影响,海拔高度场的区域平均值及其变差系数是影响网格区地面长波辐射通量的主要因素,仅仅用地表均匀假定下的区域平均参量(如平均海拔高度和平均温度)所计算的网格区地表有效辐射通量值与其真实值之间存在着一定的误差。由于地表有效辐射通量是海拔高度的非线性函数,在特定情况下,其影响相当大,可产生不容忽略的误差。相对而言,海拔高度自身非均匀性对误差的影响远大于地表温度非均匀性项及其混合扰动项所产生的误差。对于不同的地形平均高度,地形非均匀性影响的程度并不相同。平均高度较小时,非均匀性的影响几乎可以忽略,但随着地形平均高度的增加,地形非均匀性的影响程度呈非线性增长趋势。因而,在复杂地形区域,考虑次网格地形的热力作用非常必要。  相似文献   

Application of 3D empirical travel times to routine event location     

T. Nicholson 《Physics of the Earth and Planetary Interiors》2006,158(1):67-74

The unmodeled effects of lateral heterogeneity are a primary cause of event mislocation in routine methods. Approaches that account for the effect of lateral heterogeneity on travel times are commonly used in specialized studies, but some methods have recently been developed that are suitable for routine location. A variety of changes to the routine procedures have been suggested by other authors. These proposed changes are shown to be compatible to with the use of 3D travel time predictions. 3D empirical travel times are discussed in a routine context. This one step approach, based on direct use of a database of the most reliable previous observations, is shown to be suitable as an additional final step in routine procedures to give a supplementary high accuracy location. The empirical travel time approach is tested on a reference dataset of 155 ground truth events and shown to reduce epicentral mislocation by 45%. The approach is found to be particularly effective at reducing large mislocations. Improvement is demonstrated for every region represented in the dataset but particularly large improvements are shown for events in Europe, USA and Japan.  相似文献   

柑桔园林下穿透雨的分布特征   总被引：4，自引：0，他引：4       下载免费PDF全文

曹云  黄志刚  郑华  欧阳志云 《水科学进展》2007,18(6):853-857

研究了柑桔林下穿透雨的分布特征,结果表明:在测定期间,穿透雨量占总降雨量的68.3%,5月的穿透雨量最大(245.1 mm),而穿透雨率最大值(73.3%)出现在8月。穿透雨量与降雨量具有显著相关性(p<0.01),而穿透雨率与降雨量和降雨强度的相关性均达到显著水平(p<0.05)。柑桔林下穿透雨显示出明显的空间变化,各观测点间穿透雨率具有显著性的差异,而且穿透雨的空间异质性(穿透雨率的变异系数CV)随着降雨量或降雨强度的增加而降低,聚类分析也显示出穿透雨在不同观测点间具有差异性。柑桔林下穿透雨呈现明显的聚集效应。  相似文献   

Recurrence-time and frequency-slip statistics of slip events on the creeping section of the San Andreas fault in central California     

S. G. Abaimov  D. L. Turcotte  J. B. Rundle 《Geophysical Journal International》2007,170(3):1289-1299

An important question in seismic hazard assessments is the frequency-size and recurrence interval statistics at a point on a fault. Does a point on a fault obey the same statistics as earthquakes in a region do? This is a difficult question to answer because the number of repetitive earthquakes on a particular fault that have been observed is small. In order to overcome this difficulty we consider slip events on the creeping section of the San Andreas fault in central California. Sequences of up to 100 events are obtained from creepmeter records. We compare the statistical distribution of recurrence times with the Brownian passage-time, lognormal, and Weibull distributions and using goodness-of-fit tests find that the Weibull is the preferred distribution. We also consider the frequency–amplitude distribution of slip events. We find that the data clearly do not obey a Gutenberg–Richter distribution. Instead there is a uniform distribution of event sizes for a large fraction of events.  相似文献   

The Use of Comaps to Explore the Spatial and Temporal Dynamics of Fire Incidents: A Case Study in South Wales,United Kingdom*     

Jonathan Corcoran  Gary Higgs  Chris Brunsdon  Andrew Ware 《The Professional geographer》2007,59(4):521-536

This article reports on the results from a spatiotemporal analysis of disaggregate fire incident data. The innovative analysis presented here focuses on the exploration of spatial and temporal patterns for four principal fire incident categories: property, vehicle, secondary fires, and malicious false alarms. This research extends previous work on spatial exploration of spatiotemporal patterns by demonstrating the benefits of comaps and kernel density estimation in examining temporal and spatiotemporal dynamics in calls for services. Results indicate that fire incidents are not static in either time or space and that spatiotemporal variation is related to incident type. The application of these techniques has the potential to inform policy decisions both from a reactive, resource‐allocation perspective and from a more proactive perspective, such as through spatial targeting of preventive measures.  相似文献   

Numerical Modelling of the Heterogeneous Rock Fracture Process Using Various Test Techniques     

H. Y. Liu  S. Q. Kou  P.-A. Lindqvist  C. A. Tang 《Rock Mechanics and Rock Engineering》2007,40(2):107-144

Summary A series of numerical tests including both rock mechanics and fracture mechanics tests are conducted by the rock and tool (R–T^2D) interaction code coupled with a heterogeneous masterial model to obtain the physical–mechanical properties and fracture toughness, as well as to simulate the crack initiation and propagation, and the fracture progressive process. The simulated results not only predict relatively accurate physical–mechanical parameters and fracture toughness, but also visually reproduce the fracture progressive process compared with the experimental and theoretical results. The detailed stress distribution and redistribution, crack nucleation and initiation, stable and unstable crack propagation, interaction and coalescence, and corresponding load–displacement curves can be proposed as benchmarks for experimental study and theoretical research on crack propagation. It is concluded that the heterogeneous material model is reasonable and the R–T^2D code is stable, repeatable and a valuable numerical tool for research on the rock fracture process.  相似文献   

Evaluation of streambed hydraulic conductivity heterogeneity in an urban watershed   总被引：3，自引：0，他引：3  

Robert J. Ryan  Michel C. Boufadel 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(4):309-316

It has long been understood that streambed hydraulic conductivity plays an important role in surface-subsurface solute exchange. Using a portable falling head permeameter in situ, we estimated the horizontal hydraulic conductivity, K, of the near-surface streambed sediments at a total of 85 locations encompassing two depth intervals: 7.5–10 and 10–12.5 cm. The measurements were conducted in an 80 m reach of Indian Creek, a small urban stream in Philadelphia, PA, USA. We found that the ln K data within each sediment layer were Gaussian, but the combined data set was not. The results indicated that while the mean hydraulic conductivity decreased with depth, horizontal heterogeneity (e.g. the variance) increased with depth. This strong contrast between layers suggests that they should be treated as separated entities in modeling studies. Variogram analyses across the stream suggested symmetry with respect to the thalweg in the upper layer and fractality in the lower layer. The variograms along the streams suggested that the K data are random.  相似文献   

Numerical modeling of secondary migration and its applications to Chang-6 Member of Yanchang Formation (Upper Triassic), Longdong area, Ordos Basin, China     

LUO XiaoRong  YU Jian  ZHANG LiuPing  YANG Yang  CHEN RuiYin  CHEN ZhanKun  ZHOU Bo 《中国科学D辑(英文版)》2007,50(Z2):91-102

Mathematic modeling, established on the basis of physical experiments, is becoming an increasingly important tool in oil and gas migration studies. This technique is based on the observation that hydrocarbon migration tends to take relative narrow pathways. A mathematical model of hydrocarbon migration and accumulation is constructed using the percolation theory. It is then calibrated using physical experimental results, and is tested under a variety of conditions, to understand the applicability of the model in different migration cases. Through modeling, dynamic conditions of large-scale migration pathways within homogeneous formations can be evaluated. Basin-scale hydrocarbon migration pathways and their characteristics are analyzed during the model application to the Chang-8 Member of the Triassic Yanchang Formation in Longdong area of Ordos Basin. In heterogeneous formations, spatial changes in fluid potential determine the direction of secondary migration, and heterogeneity controls the characteristics and geometry of secondary migration pathways.  相似文献   

Asymptotic Coupled-Mode Expressions For Multiplet Amplitude Anomalies and Frequency Shifts On an Aspherical Earth     

Jeffrey Park 《Geophysical Journal International》1987,90(1):129-169

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A Numerical Study on Effects of Land-Surface Heterogeneity from “Combined Approach” on Atmospheric Process Part I: Principle and Method     

Zeng Xinmin  Zhao Ming  Su Bingkai 《大气科学进展》2000,17(1):103-120

1.IntroductionAnideallandsurfacemodelmustbothrealisticallydescribethelandsurfacecharacteristics(especiallytheuniversalheterogeneity)andbecomputationallyinexpensive.CurrentlyPOpularlandsurfacemodelsareallbasedon"bigfeartheory,inwhichamodelgridcellisdividedintomanypatches(e.g.,abaresoilpatchoravegetationpatch;manyregularpatchesdividedintoaccordingtogeographicallocations),andinwhichonlyinterpatchvariabilityistakenintoaccountwhileseldomintrapatchvariabilityis,whentheheterogeneityisconsidered.Even…  相似文献