城市下垫面空气动力学参数确定方法综述   总被引：1，自引：0，他引：1       下载免费PDF全文

胡张保  俞炳丰 《气象与环境学报》2008,24(5)

地表粗糙度和零平面位移是2个重要的空气动力学参数,对于城市下垫面,粗糙元的形态非常复杂,空间分布上存在较大的非均匀性,如何确定城市下垫面地表粗糙度和零平面位移目前尚无最佳方案。概述了这2个参数适用于城市非均匀下垫面的参数化方法,包括风温观测方法和粗糙元形态学方法。探讨了各自在应用过程中存在的问题及进一步的研究工作,并且提出,通过数学模型的改进和卫星遥感技术的引入,粗糙元形态学方法会有更好的发展前景：  相似文献   

不同模式分辨率和物理过程方案对贵州降水影响的对比试验   总被引：1，自引：0，他引：1  

伍红雨  陈静 《高原气象》2008,27(6)

利用MM5中尺度数值模式,在20,15和10 km模式分辨率下,采用相同的方案对贵州两次大暴雨过程进行数值模拟试验。然后选用KUO、GRELL、KAIN-FRITSCH和BETTS-MILLER(以下简称KU、GR、KF和BM)4种对流参数化方案,分别在MRF和Blackadar 2种边界层参数化方案下,对贵州汛期16个降水个例进行数值模拟试验,对模拟结果进行对比分析并与实况资料进行比较,结果表明:预报的降水落区对参数化方案敏感。随着分辨率的提高,降水分布与实况更接近。MM5模式的这4种积云参数化方案对环流的模拟较好,但模拟降水的效果有差别:对50 mm以下的降水,GR方案的预报效果较好,KF方案则较差;对50 mm以上的降水,BM、KF方案的预报效果一般较好;选择MRF或Blackadar的边界层参数化方案对降水预报效果区别不大。选择BM或KF积云对流参数化方案、混合相显式水汽方案、MRF边界层参数化方案和云辐射方案的组合,取得了优于其他组合的预报结果。  相似文献   

The Scaling Behaviour of a Turbulent Kinetic Energy Closure Model for Stably Stratified Conditions   总被引：2，自引：1，他引：1  

Peter Baas  Stephan R. de Roode  Geert Lenderink 《Boundary-Layer Meteorology》2008,127(1):17-36

We investigate the scaling behaviour of a turbulent kinetic energy (TKE) closure model for stably stratified conditions. The mixing length scale for stable stratification is proportional to the ratio of the square root of the TKE and the local Brunt–Väisälä frequency, which is a commonly applied formulation. We analyze the scaling behaviour of our model in terms of traditional Monin–Obukov Similarity Theory and local scaling. From the model equations, we derive expressions for the stable limit behaviour of the flux–gradient relations and other scaling quantities. It turns out that the scaling behaviour depends on only a few model parameters and that the results obey local scaling theory. The analytical findings are illustrated with model simulations for the second GABLS intercomparison study. We also investigate solutions for the case in which an empirical correction function is used to express the eddy diffusivity for momentum as a function of the Richardson number (i.e. an increasing turbulent Prandtl number with stability). In this case, it seems that for certain parameter combinations the model cannot generate a steady-state solution. At the same time, its scaling behaviour becomes unrealistic. This shows that the inclusion of empirical correction functions may have large and undesired consequences for the model behaviour.  相似文献   

英国温室气体排放贸易制度的实践与评价   总被引：1，自引：0，他引：1  

吴向阳 《气候变化研究进展》2007,3(1):58-061

温室气体排放贸易作为一种经济激励型的环境管理手段,对企业减少温室气体排放有成本效率作用。详细介绍了英国温室气体排放贸易制度框架,并对其政策的效果及存在的问题进行了评价。  相似文献   

Adaptive multi-scale parameterization for one-dimensional flow in unsaturated porous media     

Mohamed Hayek  François LehmannPhilippe Ackerer 《Advances in water resources》2008

In the analysis of the unsaturated zone, one of the most challenging problems is to use inverse theory in the search for an optimal parameterization of the porous media. Adaptative multi-scale parameterization consists in solving the problem through successive approximations by refining the parameter at the next finer scale all over the domain and stopping the process when the refinement does not induce significant decrease of the objective function any more. In this context, the refinement indicators algorithm provides an adaptive parameterization technique that opens the degrees of freedom in an iterative way driven at first order by the model to locate the discontinuities of the sought parameters. We present a refinement indicators algorithm for adaptive multi-scale parameterization that is applicable to the estimation of multi-dimensional hydraulic parameters in unsaturated soil water flow. Numerical examples are presented which show the efficiency of the algorithm in case of noisy data and missing data.  相似文献   

Parameterization of bedform morphology and defect density with fingerprint analysis techniques     

Adam Skarke  Arthur C. Trembanis 《Continental Shelf Research》2011,31(16):1688-1700

A novel method for parameterizing the morphology of seafloor ripples with fingerprint analysis numerical techniques is presented. This fully automated analysis tool identifies rippled areas in two-dimensional imagery of the seafloor, and returns ripple orientation and wavelength as well as a new morphological parameter, the spatial density of ripple defects. In contrast to widely used manual and spectral parameterization methods, this new technique yields a unique probability distribution for each derived parameter, which describes its spatial variability across the sampled domain. Here we apply this new analysis technique to synthetic and field collected side-scan sonar seafloor images in order to assess the methods capacity to define bed geometry across a wide range of simulated and observed morphological conditions. The resulting orientation and wavelength values compare favorably with those of the existing manual and spectral parameterization methods, and are superior under environmental conditions characterized by low signal to noise ratios as well as high planform ripple sinuosity. Furthermore, the resulting ripple defect density values demonstrate correlation with ripple orientation, wave direction, and the Shields parameter, which is consistent with recent investigations that have theoretically linked this parameter to hydrodynamic forcing conditions. The presented fingerprint analysis method surpasses the capacity of existing methods for ripple parameterization and promises to yield greater insight into theoretical and applied problems associated with the temporal and spatial variability of ripple morphology across a wide spectrum of marine environments.  相似文献   

二阶精度半隐式半拉格朗日轨迹计算和时间积分方案在GRAPES区域模式中的应用     

张旭  黄伟  陈葆德 《气象学报》2015,73(3):557-565

将两时间层稳定外插方案(Stable Extrapolation Two-Time-Level Scheme,SETTLS)引入GRAPES区域模式,并将其用于上游点和非线性项的时间外插计算。对线性项采用二阶精度的非中央权重时间平均,并取等温参考大气的温度大于实际大气平均温度,以保证半隐式积分方案的稳定性。原GRAPES时间积分方案对线性项做一阶非中央权重时间平均,对参考大气的选择并无限制,而为保证稳定性,须取较大的非中央权重系数,但非中央权重系数会对低波数波动产生较强的衰减作用。理想试验结果表明,相比原GRAPES半隐式半拉格朗日(SISL)时间积分方案,新SISL时间积分方案计算稳定且对波动的衰减作用较弱。  相似文献   

湖泊数值模拟研究现状综述   总被引：1，自引：0，他引：1  

任晓倩  孙菽芬  陈文  刘辉志 《地球科学进展》2013,28(3):347-356

作为陆面过程的重要组成部分,湖泊在天气气候预测中的作用得到了相关研究者的广泛关注,并成为大气科学研究领域中的一个热点.主要综述了当前湖泊模式的基本类型、所考虑的关键物理过程及其参数化方案,并尝试分析了各个方案的优劣以及模拟效果.相关研究表明,现有的湖泊模式对浅湖的模拟比较成熟,而对深湖和冰湖的模拟有待改进.未来的研究亟需构筑适用于大湖、深湖以及冰湖的参数化方案,发展能全面模拟各类型湖泊的数值模式,并且湖泊数值模拟的改进依赖于今后更多高质量的全球湖泊观测结果.  相似文献   

The structure of tuna access agreements in the Western and Central Pacific Ocean: Lessons for Vessel Day Scheme planning     

Elizabeth Havice 《Marine Policy》2010

The tuna industry in the Western and Central Pacific Ocean (WCPO) is one of the largest and most valuable fisheries in the world. Since the 1980s, Pacific island countries have used licensing agreements with foreign fishing interests—known as access agreements—to earn tuna-related revenue and control the environmental impacts of fishing, with only minimal success. To date, there has been little work detailing the structure of access agreements and assessing how this structure relates to economic and environmental outcomes in the sector. This article helps to fill this gap by providing an overview of various access structures and a detailed empirical assessment of how these structures are applied in access agreements between Pacific island countries and the major foreign fishing interests active in the WCPO. This analysis is placed in the context of evolving regional fisheries management structures. The study reveals that while there is no uniform formula for access agreements, each structure is subject to distinct political, economic and environmental considerations that influence outcomes for Pacific island countries. As Pacific island countries develop the mechanism to allocate fishing rights under the new Vessel Day Scheme, drawing on their long history with access agreements will assist efforts to use access to achieve policy objectives. Improved transparency will enable Pacific island countries to identify successes and problems and adapt the Vessel Day Scheme allocation mechanisms accordingly.  相似文献   

A Modified Neural Network for Improving River Flow Prediction/Un Réseau de Neurones Modifié pour Améliorer la Prévision de L'Écoulement Fluvial     

《水文科学杂志》2013,58(2)

Abstract

Artificial neural network (ANN) models provide huge potential for simulating nonlinear behaviour of hydrological systems. However, the potential of ANN is yet to be fully exploited due to the problems associated with improving the model generalization performance. Generalization refers to the ability of a neural network to correctly process input data that have not been used for calibrating the neural network model. In the hydrological context, better generalization performance implies higher precision of forecasting. The primary objectives of this study are to explore new measures for improving the generalization performance of an ANN-based rainfall–runoff model, and to evaluate the applicability of the new measures. A modified neural network model (entitled goal programming (GP) neural network) for modelling the rainfall–runoff process has been developed, in which three enhancements are made as compared to the widely-used backpropagation (BP) network. The three enhancements are (a) explicit integration of hydrological prior knowledge into the neural network learning; (b) incorporation of a modified training objective function; and (c) reduction of network sensitivity to input errors. Seven watersheds across a range of climatic conditions and watershed areas in China were selected for examining the alternative networks. The results demonstrate that the GP consistently outperformed the BP both in the calibration and verification periods and three proposed measures yielded improvement of performance.  相似文献