1951-2016年秦巴山区霜期变化的时空特征分析     

楼俊伟  张鑫  王可欣  王智楷 《沙漠与绿洲气象(新疆气象)》2019,13(5):82-88

依据秦巴山区96个气象站点1951—2016年逐日最低气温数据,利用一元线性回归、M-K突变检验法和Cressman插值法分析了初、终霜日和霜期变化的时空特征,并对终霜日和霜期的变化趋势及其与海拔高度的关系进行了分析,结果表明:在时间变化上,秦巴山区平均初霜日呈现出推迟的趋势,且在1960年左右发生了显著突变,而平均终霜日则与之相反,表现出提前的趋势,平均霜期也呈现出显著的减少趋势,且在20世纪60年代中期至70年代末期间表现得十分明显;空间变化上,秦巴山区初霜日和霜期呈现出较大的南北差异,而终霜日则表现为较大的东西差异;在与海拔分布的关系上,秦巴山区部分地区终霜日和霜期的变化趋势有明显的海拔依赖性,表现为西部和中东部地区终霜日的变化趋势随海拔高度的增加而减少,北部地区霜期的变化趋势随着海拔高度的增加而减少。  相似文献   

Three-dimensional RITSS large displacement finite element method for penetration of foundations into soil     

L. Yu  J. Liu  X.J. Kong  Y. Hu 《Computers and Geotechnics》2008,35(3):372-382

The Remeshing and Interpolation Technique with Small Strain (RITSS) approach has been developed to deal with 3-D geotechnical problems in this paper. Unstructured 20-node hexahedral element is found to work well for predicting collapse loads accurately for 3-D undrained geotechnical problems involving material incompressibility. Remeshing is automatically accomplished by ANSYS program. With remeshing and interpolation, small fluctuations appear in the load–deformation results. In order to minimize these fluctuations, different increment sizes and remeshing frequencies are explored. Meanwhile, various 3-D interpolation methods are compared, and the unique element division method is found to work best. The results of two numerical applications are presented for a 3-D strip footing penetrating deeply into uniform clay and a square foundation into normally consolidated clay. The computed bearing capacity responses are compared with other numerical or conventional results. The results show that the present method is accurate and efficient for 3-D large displacement foundation penetration problems.  相似文献   

多连通域中的插值序列     

张庆德 《成都信息工程学院学报》1987,(2)

本文给出了多连通域(由有限个连续统所界)上点列为H~∞(D)插值序列的几个等价条件。这些条件是保形不变的。  相似文献   

华北区年高温日数区域平均方法及趋势分析   总被引：6，自引：4，他引：6  

张德宽  姚华栋  杨贤为  廖要明 《高原气象》2006,25(4):750-753

利用华北地区33个代表站1961—2002年间的年高温日数序列,采用均生函数和最优子集回归法,设计出具有较强拟合能力和未来趋势预测的数理统计模型。该模型能较好地拟合历史实况,其信度达到了99%;也使用该模型做出华北地区2003—2005年3年的高温日数趋势预测,对2003年和2004年做出的趋势预测效果较好。  相似文献   

On unbiased backtransform of lognormal kriging estimates   总被引：4，自引：0，他引：4  

Jorge Kazuo Yamamoto 《Computational Geosciences》2007,11(3):219-234

Lognormal kriging is an estimation technique that was devised for handling highly skewed data distributions. This technique takes advantage of a logarithmic transformation that reduces the data variance. However, backtransformed lognormal kriging estimates are biased because the nonbias term is totally dependent on a semivariogram model. This paper proposes a new approach for backtransforming lognormal kriging estimates that not only presents none of the problems reported in the literature but also reproduces the sample histogram and, consequently, the sample mean.  相似文献   

On selection of kernel parametes in relevance vector machines for hydrologic applications     

Shivam Tripathi  Rao S. Govindaraju 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(6):747-764

Recent advances in statistical learning theory have yielded tools that are improving our capabilities for analyzing large and complex datasets. Among such tools, relevance vector machines (RVMs) are finding increasing applications in hydrology because of (1) their excellent generalization properties, and (2) the probabilistic interpretation associated with this technique that yields prediction uncertainty. RVMs combine the strengths of kernel-based methods and Bayesian theory to establish relationships between a set of input vectors and a desired output. However, a bias–variance analysis of RVM estimates revealed that a careful selection of kernel parameters is of paramount importance for achieving good performance from RVMs. In this study, several analytic methods are presented for selection of kernel parameters. These methods rely on structural properties of the data rather than expensive re-sampling approaches commonly used in RVM applications. An analytical expression for prediction risk in leave-one-out cross validation is derived. For brevity, the effectiveness of the proposed methods is assessed first by data generated from the benchmark sinc function, followed by an example involving estimation of hydraulic conductivity values over a field based on observations. It is shown that a straightforward maximization of likelihood function can lead to misleading results. The proposed methods are found to yield robust estimates of parameters for kernel functions.  相似文献   

DEM-induced errors in developing a quasi-geoid model for Africa   总被引：2，自引：0，他引：2  

C. L.?MerryEmail author 《Journal of Geodesy》2003,77(9):537-542

Errors in digital elevation models (DEMs) will introduce errors in geoid and quasi-geoid models, via their use in interpolating free-air gravity anomalies and (in the case of the quasi-geoid) their use in computing the Molodensky G ₁ term. The effects of these errors and those of datum shifts are assessed using three independent DEMs for a test region in South Africa. It is shown that these effects are significant and that it is important to choose the best-possible DEM for use in geoid and quasi-geoid modelling. Acknowledgments.The land gravity data used for this research were provided by the South African Council for Geoscience. Marine gravity anomalies were provided by the Danish National Survey and Cadastre (Kort & Matrikelstyrelsen). The GLOBE DEM was provided by the US National Geophysical Data Centre, and the CDSM DEM was provided by the South African Chief Directorate for Surveying and Mapping. The constructive comments of the reviewers are gratefully acknowledged.  相似文献   

Correlation functions of rainfall field and their application in network design in the tropics     

D. A. Mooley  P. M. Mohamed Ismail 《Pure and Applied Geophysics》1982,120(2):249-260

The study examines the correlation function of tropical monsoon rainfall on monthly, seasonal and annual time scales and obtains the relationship between this function and the distance. The area selected for study is Vidarbha with a fairly dense network of rain gauges. Vidarbha is a meteorological sub-division of the state of Maharashtra in India. Utilizing the relationship between the correlation function of the rainfall field and the distance, the errors of optimum interpolation of rainfall at a point have been computed by applying the method of optimum interpolation byGandin (1970). Relationships between the errors of interpolation and distance have been evaluated and from this the maximum spacing allowed between rain gauges for a specified tolerable error in interpolation has been estimated for each of the periods.  相似文献   

数字地形模型的质量控制     

万志龙 《测绘学院学报》1989,(1)

本文在分析、研究现有解决DTM质量控制的各种方法的基础上,提出了利用实测断面数据的所谓“断面内插分析法”。其特点是全面考虑了各种因素的影响,完整而可靠地描述各种因素对最终DTM数据精度的影响。实验证明:该法是最稳定、最可靠的,它具有简便易行的特点,几乎不增加多少作业负担,易于作业人员所接受,为DTM数据获取提供了一套非常实用的质量控制方案。  相似文献   

插值预报的一种新方法及其在降水预报中的应用   总被引：1，自引：1，他引：0  

曹杰  陶云 《气象科学》2000,20(4):516-521

本文针对经典插值预报方法存在的不足,遵循插值预报的基本原理,提出了插值预报的一种新方法,此方法的实质是考虑了预报系统中不同预报因子对系统的最后演变结果的不同作用,将此方法应用于云南１８个测站五月雨量的预报中,结果表明,此方法无论在历史预报方面还是在外推预报方面均具有良好的稳定性和预报精度。  相似文献