长岭山北麓断裂上新发现的地震地表破裂带   总被引：1，自引：0，他引：1       下载免费PDF全文

柳煜  杨斌  李明永  王爱国  刘洪春 《地震工程学报》2006,28(4):319-326

通过野外地震地质调查,在甘肃省古浪县、景泰县交界处的长岭山地区新发现了丰富的线状分布的地震地表破裂现象,表现为基岩崩塌、黄土滑坡、地震裂缝、地震土林、地震沟槽、陷落坑以及断层陡坎等,局部可见残留的破裂滑动自由面。其分布严格受长岭山北麓活动断裂控制。通过地震地表破裂带本身的特征分析、年代学分析、地表破裂带长度与震级的拟合关系以及结合区域活动断裂资料研究,认为该地震地表破裂带可能为1927年古浪8.0级地震的产物。  相似文献   

Evaluation of the Urban Tile in MOSES using Surface Energy Balance Observations     

M. J. Best  C. S. B. Grimmond  Maria Gabriella Villani 《Boundary-Layer Meteorology》2006,118(3):503-525

The UK Met Office has introduced a new scheme for its urban tile in MOSES 2.2 (Met Office Surface Exchange Scheme version 2.2), which is currently implemented within the operational Met Office weather forecasting model. Here, the performance of the urban tile is evaluated in two urban areas: the historic core of downtown Mexico City and a light industrial site in Vancouver, Canada. The sites differ in terms of building structures and mean building heights. In both cases vegetation cover is less than 5%. The evaluation is based on surface energy balance flux measurements conducted at approximately the blending height, which is the location where the surface scheme passes flux data into the atmospheric model. At both sites, MOSES 2.2 correctly simulates the net radiation, but there are discrepancies in the partitioning of turbulent and storage heat fluxes between predicted and observed values. Of the turbulent fluxes, latent heat fluxes were underpredicted by about one order of magnitude. Multiple model runs revealed MOSES 2.2 to be sensitive to changes in the canopy heat storage and in the ratio between the aerodynamic roughness length and that for heat transfer (temperature). Model performance was optimum with heat capacity values smaller than those generally considered for these sites. The results suggest that the current scheme is probably too simple, and that improvements may be obtained by increasing the complexity of the model.  相似文献   

Improved Representation of Land-surface Heterogeneity in a Non-hydrostatic Numerical Weather Prediction Model   总被引：2，自引：1，他引：2  

Felix Ament  Clemens Simmer 《Boundary-Layer Meteorology》2006,121(1):153-174

This study focuses on the relevance of accurate surface parameters, in particular soil moisture, and of parameterizations for heterogeneous land surfaces, for the prediction of sensible and latent heat fluxes by a mesoscale weather forecast model with horizontal grid resolution of 7 km. The analysis is based on model integrations for a 30-day period, which are compared both to flux measurements obtained from the LITFASS-2003 field experiment and to high-resolution-model (1-km grid spacing) results. At first, the relevance of improved parameter sets and input data compared to usual operational practice for an accurate prediction of near-surface fluxes is shown and discussed. It is demonstrated that an observation-based land-surface assimilation scheme leads to an improved soil moisture analysis, which is shown to be essential for the realistic simulation of surface fluxes. Secondly, the implementation of two efficient parameterization strategies for subgrid-scale variability of the surface, the mosaic and the tile approach, is presented. Using these methods, the simulations are in better agreement with measurements than simulations with simple aggregation methods that use effective surface parameters. Integrations with the mosaic approach reproduce high resolution simulations very well and more accurately than simulations with the tile method. Finally, the high resolution simulations are analyzed to justify and discuss the approximations underlying both methods.  相似文献   

Characteristics of secondary circulations over an inhomogeneous surface simulated with large-eddy simulation     

Thara V. Prabha  Anandakumar Karipot  Michael W. Binford 《Boundary-Layer Meteorology》2007,123(2):239-261

Large-eddy simulation is used to study secondary circulations in the convective boundary layer modulated as a result of horizontally varying surface properties and surface heat fluxes over flat terrain. The presence of heat flux heterogeneity and its alignment with respect to geostrophic wind influences the formation, strength and orientation of organized thermals. Results show boundary-attached roll formation along heat flux maxima in the streamwise direction. The streamwise organization of the updrafts and downdrafts formed downwind of heterogeneities leads to counter-rotating secondary circulations in the crosswind plane. The distribution of resolved-scale pressure deviations shows large pressure gradients in the crosswind plane. Spanwise and vertical velocity variances and heat flux profiles depict considerable spatial variability compared to a homogeneous forest simulation. Secondary circulations are observed for various ambient wind scenarios parallel and perpendicular to heterogeneities. In the presence of increased wind speed, thermals emerging from the heat flux heterogeneity are elongated, and organize along and downwind of large-scale heterogeneity in the streamwise direction. Simulation with a reduced heat flux shows a shallower circulation with a lower aspect ratio. Point measurements of heat flux inside the roll circulation could be overestimated by up to 15–25% compared to a homogeneous case.  相似文献   

The effect of mountainous topography on moisture exchange between the “surface” and the free atmosphere   总被引：1，自引：0，他引：1  

Andreas P. Weigel  Fotini K. Chow  Mathias W. Rotach 《Boundary-Layer Meteorology》2007,125(2):227-244

Typical numerical weather and climate prediction models apply parameterizations to describe the subgrid-scale exchange of moisture, heat and momentum between the surface and the free atmosphere. To a large degree, the underlying assumptions are based on empirical knowledge obtained from measurements in the atmospheric boundary layer over flat and homogeneous topography. It is, however, still unclear what happens if the topography is complex and steep. Not only is the applicability of classical turbulence schemes questionable in principle over such terrain, but mountains additionally induce vertical fluxes on the meso-γ scale. Examples are thermally or mechanically driven valley winds, which are neither resolved nor parameterized by climate models but nevertheless contribute to vertical exchange. Attempts to quantify these processes and to evaluate their impact on climate simulations have so far been scarce. Here, results from a case study in the Riviera Valley in southern Switzerland are presented. In previous work, measurements from the MAP-Riviera field campaign have been used to evaluate and configure a high-resolution large-eddy simulation code (ARPS). This model is here applied with a horizontal grid spacing of 350 m to detect and quantify the relevant exchange processes between the valley atmosphere (i.e. the ground “surface” in a coarse model) and the free atmosphere aloft. As an example, vertical export of moisture is evaluated for three fair-weather summer days. The simulations show that moisture exchange with the free atmosphere is indeed no longer governed by turbulent motions alone. Other mechanisms become important, such as mass export due to topographic narrowing or the interaction of thermally driven cross-valley circulations. Under certain atmospheric conditions, these topographical-related mechanisms exceed the “classical” turbulent contributions a coarse model would see by several times. The study shows that conventional subgrid-scale parameterizations can indeed be far off from reality if applied over complex topography, and that large-eddy simulations could provide a helpful tool for their improvement.  相似文献   

2005年10月8日巴基斯坦7.8级地震热红外异常   总被引：4，自引：1，他引：4       下载免费PDF全文

钟美娇  张元生 《地震工程学报》2007,29(2):137-140

收集了2005年巴基斯坦7.8级地震区Noaa17/AVHRR的2004-2005年的热红外遥感资料,并进行地表温度反演,得到了以震中为中心7°×7°范围的地表温度值。经热红外图像解译与构造关系对比分析,表明热红外解译图像与构造分布具有一致性。震源区地表温度时间序列显示:震前大约3个月内震源区存在明显的热红外异常。  相似文献   

不同标度震级关系和台基影响问题探讨   总被引：2，自引：1，他引：2  

张宏志  刁桂苓  赵明淳  王勤彩  张骁  黄媛 《中国地震》2007,23(2):141-146

利用近年中国数字地震台网观测报告中的中国及邻区地震目录资料,取能够同时计算面波震级MS和近震震级ML的地震,拟合出2种震级之间的关系,发现与过去使用30余年的换算公式存在系统差别。考虑现代化地震数字观测系统有动态范围大、频带宽、台站多、覆盖区域广、测定精度高的特点,由此拟合的关系应当更可靠。考虑不同误差因素统计面波震级MS和近震震级ML的关系表明,2种震级之间换算和不换算的差别并不大,因此建议MS和ML震级之间不换算为宜。分析地震台站的场地响应发现:一些基岩台的放大因子在1附近,场地响应不随频率变化;处于沉积土层的台站,放大因子在低频段大于1,高频段小于1;还有一些台站在某个频段范围大于1,或者小于1。另外,沉积土层台站的单台震级和台网平均震级差也随周期增大,呈现由负到正的增长趋势。看来并不存在固定的台站校正系数,因此不能把台站校正作为提高震级测定精度的方法。  相似文献   

Impact of water overexploitation on highland lakes of eastern Ethiopia   总被引：1，自引：0，他引：1  

Tamiru Alemayehu  Wagari Furi  Dagnachew Legesse 《Environmental Geology》2007,52(1):147-154

The eastern Ethiopian highland is endowed with large potential of water resources in terms of rainfall, groundwater and surface water. Yet, due to overpumping of lake water and groundwater and environmental degradation, Lakes Haromaya and Adele have completely dried up. The environmental degradation, due to deforestation and clearing of land for farming, has increased the rate of siltation in the lakes that dramatically decreases the lakes’ volume and surface albedo, which increased the rate of evaporation. The impact of these factors is aggravated due to decreasing net recharge to the lake and the alluvial aquifer. Over the last 35 years, pumping of lake water for irrigation, mainly for subsistence farming, domestic and industrial use shows an increasing trend. Hence, the available water for drinking and industrial purposes decreased drastically. In this research, classical Penman aerodynamic combined energy budget, Penman nomogram methods, conventional soil moisture water balance method and Penman–Monteith model were adopted to estimate free evaporation, actual and potential evapotranspirations. The results indicate that evaporation is the dominant factor for the loss of water and water abstraction is 316% higher than the effective precipitation, which is 110 mm/year. Therefore, overexploitation of the available resources has played an aggravating role for the loss of the lakes in the area. The main cause for such resource depletion is the lack of integrated water resources management strategies. The current water shortage in the area has mainly affected urban residents of Harar, Awoday and Alemaya towns and the surrounding villages, which depend heavily on the two lakes. To alleviate the current crises interbasin water transfer and rainwater harvesting would be possible alternatives besides ameliorating environmental situation of the basin.  相似文献   

Non-destructive estimation of potato leaf chlorophyll from canopy hyperspectral reflectance using the inverted PROSAIL model     

Elizabeth J. Botha  Brigitte Leblon  Bernie Zebarth  James Watmough   《International Journal of Applied Earth Observation and Geoinformation》2007,9(4):360-374

Optimizing nitrogen (N) fertilization in crop production by in-season measurements of crop N status may improve fertilizer N use efficiency. Hyperspectral measurements may be used to assess crop N status by estimating leaf chlorophyll content. This study evaluated the ability of the PROSAIL canopy-level reflectance model to predict leaf chlorophyll content. Trials were conducted with two potato cultivars under different N fertility rates (0–300 kg N ha⁻¹). Canopy reflectance, leaf area index (LAI) and leaf chlorophyll and N contents were measured. The PROSAIL model was able to predict leaf chlorophyll content with reasonable accuracy later in the growing season. The low estimation accuracy earlier in the growing season could be due to model sensitivity to non-homogenous canopy architecture and soil background interference before full canopy closure. Canopy chlorophyll content (leaf chlorophyll content × LAI) was predicted less accurately than leaf chlrophyll content due to the low estimation accuracy of LAI for values higher than 4.5.  相似文献   

基于室内光谱测量的玉米单叶偏振与二向性反射关系研究     

宋开山  张柏  赵云升  王宗明  杜佳 《遥感学报》2007,11(5):632-640

本研究利用多角度光度计实测了玉米单叶的偏振反射比与二向反射比数据。该光度计能够在不同的观测天顶角、入射天顶角和方位角下测量目标物的偏振反射和二向反射,获得地物目标在2π空间的多角度观测数据。通过分析实测的偏振反射和二向反射数据,得出了玉米单叶的偏振反射与二向反射之间关系密切,最大与最小偏振反射比之和的平均数约等于同等观测条件下玉米叶片的二向反射比。该研究成果为植被遥感监测做出了一种新的尝试,并且对偏振光遥感、多角度遥感的深入研究与应用提供了依据。  相似文献