青藏高原东边缘山区极值风速推算方法的研究   总被引：2，自引：0，他引：2  

李林  李卫林  王振宇  姚志国  朱西德 《高原气象》2006,25(6):1028-1033

利用1971—2001年青藏高原东边缘地区12个气象台站风资料,分析了影响极值风速的主要因子,通过对地形的参数化处理,建立了极值风速随海拔高度和地形参数变化的拟合模型,可推算该地山区的极值风速,并利用山区临时观测资料对拟合模型进行了检验。结果表明,利用引入地形参数所建立的极值风速拟合模型来推算山区极值风速具有一定的可行性。  相似文献   

Paleoclimate Modelling at the Institute of Atmospheric Physics, Chinese Academy of Sciences   总被引：1，自引：1，他引：1  

姜大膀  张仲石 《大气科学进展》2006,23(6):1040-1049

Paleoclimate modelling is one of the core topics in the Past Global Changes project under the International Geosphere-Biosphere Programme and has received much attention worldwide in recent decades. Here we summarize the research on the Paleoclimate modeling, including the Holocene, Last Glacial Maximum, and pre-Quaternary climate intervals or events performed at the Institute of Atmospheric Physics under the Chinese Academy of Sciences (IAP/CAS) for over one decade. As an attempt to review these academic activities, we emphasize that vegetation and ocean feedbacks can amplify East Asian climate response to the Earth’s orbital parameters and atmospheric CO2 concentration at the mid-Holocene. At the Last Glacial Maximum, additional cooling in interior China is caused by the feedback effects of East Asian vegetation and the ice sheet over the Tibetan Plateau, and the regional climate model RegCM2 generally reduces data-model discrepancies in East Asia. The simulated mid-Pliocene climate is characterized by warmer and drier conditions as well as significantly weakened summer and winter monsoon systems in interior China. On a tectonic timescale, both the Tibetan Plateau uplift and the Paratethys Sea retreat play important roles in the formation of East Asian monsoon-dominant environmental pattern during the Cenozoic.  相似文献   

Maximal Overlap Wavelet Statistical Analysis With Application to Atmospheric Turbulence     

Charles R. Cornish  Christopher S. Bretherton  Donald B. Percival 《Boundary-Layer Meteorology》2006,119(2):339-374

Statistical tools based on the maximal overlap discrete wavelet transform (MODWT) are reviewed, and then applied to a dataset of aircraft observations of the atmospheric boundary layer from the tropical eastern Pacific, which includes quasi-stationary and non-stationary segments. The wavelet methods provide decompositions of variances and covariances, e.g. fluxes, between time scales that effectively describe a broadband process like atmospheric turbulence. Easily understood statistical confidence bounds are discussed and applied to these scale decompositions, and results are compared to Fourier methods for quasi-stationary turbulence. The least asymmetric LA(8) wavelet filter yields coefficients that exhibit better uncorrelatedness across scales than the Haar filter and is better suited for decomposition of broadband turbulent signals. An application to a non-stationary segment of our dataset, namely vertical profiles of the turbulent dissipation rate, highlights the flexibility of wavelet methods.  相似文献   

中国春季气温异常变率的非线性特征   总被引：2，自引：0，他引：2  

徐同  郭品文  居丽丽 《气象与环境科学》2007,30(2):9-12

运用一种基于神经网络的非线性主成分分析法(NLPCA)对中国1951-2003年53 a春季气温距平场进行分析,结果表明,春季气温异常变率具有显著的非线性特征,当非线性主元u分别取最大值和最小值时,对应的空间气温异常分布型具有显著的非对称性.  相似文献   

基于虚拟观测的病态问题解法   总被引：2，自引：0，他引：2  

冯光财  戴吾蛟  朱建军  陈正阳 《测绘科学》2007,32(2):38-39,66

在大地测量数据处理领域中,处理病态问题的主要方法有:岭估计方法、奇异值分解法(SVD)、Tik-honov正则化方法等,但是这些方法大多数是强调数学上的意义,没有充分联系大地测量的实际情况,因此不利于在测绘领域病态问题本质的理解和研究。为使病态问题的求解具有实际的物理意义,提出了基于虚拟观测的岭估计方法。该方法将先验约束条件作为一类互相独立的虚拟观测值,从而把病态问题转化为测量平差问题,然后运用Helmert方差估计法来确定岭参数。该方法还可以得到的参数之间的权矩阵,用它来代替虚拟观测值的权矩阵,重新对参数进行计算,则实现了该方法向广义岭估计的推广。实际算例分析的结果表明该方法不仅计算简单而且能保证结果精确。  相似文献   

Non-classical types of loess     

M.H. Iriondo  D.M. Kröhling 《Sedimentary Geology》2007,202(3):352-368

The purpose of this contribution is to describe the sequence of physical and chemical processes resulting in the sediment-type named loess, a fine-grained sediment deposit of universal occurrence. Owing to historical causes, loess has been (and still is) implicitly linked to glacial/periglacial environments among most naturalists. However it is known today that most eolian dust is deflated from tropical deserts. Hence, that sequence of processes is more comprehensive than the former narrow cold scenario. Six examples of different “non-classical” cases (from South America and Europe) that fit well to the loess definition are developed: 1) volcanic loess in Ecuador: pyroclastic eruptions/valley wind/mountain praire/silica structuring; 2) tropical loess in northeastern Argentina, Brazil and Uruguay: deflation of river and fan splays/savanna/iron sesquioxide structuring; 3) gypsum loess in northern Spain: destruction of anhydrite/gypsiferous layers in a dry climate/valley wind/Saharian shrub peridesert/gypsum structuring; 4) trade-wind deposits in Venezuela and Brazil: deflation in tidal flats/trade wind into the continent/savanna/iron hydroxide structuring; 5) anticyclonic gray loess in Argentina: continental anticyclone on plains/anti-clockwise winds and whirls/steppe/carbonate structuring. All these non-classical types conform to the accepted loess definitions and they also share the most important field characteristics of loess such as grain size, friability, vertical or sub-vertical slopes in outcrops, subfusion and others. Other cases can probably be recognized when systematically scrutinized.  相似文献   

A numerical study on 2-D compressive wave propagation in rock masses with a set of joints along the radial direction normal to the joints   总被引：1，自引：0，他引：1  

W.D. Lei  A.M. Hefny  S. Yan  J. Teng 《Computers and Geotechnics》2007,34(6):508-523

An explosion in a borehole or an accidental explosion in a tunnel will generate a two-dimensional (2-D) compressive wave that travels through the surrounding rock mass. For the problem of 2-D compressive wave propagation in a rock mass with parallel joints in the radial direction normal to the joints, parametric studies on the transmission ratio and the maximum rebound ratio are performed in universal distinct element code. The variation of the transmission ratio with the ratio of joint spacing to wavelength is generalized into a characteristic curve, which can be used as a prediction model for estimating the transmission ratio. The relationship between the maximum rebound ratio and the influence factors is obtained in charts. The charts can be used as a prediction model for estimating the maximum rebound ratio. The proposed prediction models for estimating the transmission ratio and the maximum rebound ratio are applied to a field explosion test, Mandai test in Singapore. The minimum possible values of peak particle velocity (PPV) at the monitoring points are estimated by using the proposed prediction model for estimating the transmission ratio along the radial direction normal to the joints. On the other hand, the maximum possible values of PPV are estimated by using the proposed prediction model for estimating the maximum rebound ratio along the same radial direction. The comparison shows a good agreement between the field-recorded PPVs and the estimated range of PPVs given by the minimum possible PPVs and the maximum possible PPVs at the monitoring points in Mandai test. The good agreement between the estimated and field-recorded values validates the proposed prediction models for estimating peak particle velocity in a rock mass with a set of joints due to application of a compressive wave at the boundary of a tunnel or a borehole.  相似文献   

GRACE和SLR观测的地球动力学扁率最大熵谱及小波相关分析          下载免费PDF全文

张子占  陆洋  许厚泽 《地球物理学报》2007,50(5):1383-1389

卫星重力测量技术的实现为测定地球动力学扁率提供了新的方式和途径，GRACE卫星是目前最新的重力测量卫星，据其恢复的低阶重力场较以往精度得到大大提高，然而其观测地球动力学扁率（二阶项）却与卫星激光测距（SLR）结果相差较大.本文采用最大熵谱和小波分析方法对GRACE和SLR观测的地球动力学扁率时间序列信号进行定量比较分析，结果表明：GRACE观测的地球动力学扁率年际周期变化振幅仅为SLR观测结果的25%，并且目前GRACE观测的地球动力学扁率数据中含有系统输入信息和相位差，但前者较后者包含有较强的短周期（2～6月）信息.造成这种差异的主要原因可能来自于GRACE与SLR全球观测数据时空分布不同.  相似文献   

基于尺度因素的地下水随机分析          下载免费PDF全文

史良胜  杨金忠  林琳  李少龙 《水科学进展》2007,18(1):39-43

针对小尺度的各态历经假设的失效,研究了小尺度上多孔介质特性参数统计特征。利用基于K-L(Karhunen-Loeve)展开和混沌展开的谱模型,分析了尺度大小对地下水流动的影响。结果表明,尺度大小导致了特征值系列和特征函数系列的变化,尺度的变化对水头、含水量、流速影响程度不同;水头和流速方差与尺度相关,尺度越大,水头和流速方差越大;研究尺度的变化对水头、含水量、流速均值产生的影响较小。  相似文献   

导航卫星原子钟频率漂移特性分析   总被引：2，自引：0，他引：2  

郭海荣  杨生  何海波 《全球定位系统》2007,32(6):5-10

介绍了原子钟频漂定义，总结了频率漂移率测试评定方法，比较分析了不同噪声情况下的频率漂移率估计方法，并用实验室真空状态铷钟的频率偏差数据和GPS卫星钟的精密星历数据进行了计算分析，表明铷钟都有明显频漂，GPSIIR铷钟的日漂移率在10^-15。量级，而铯钟频漂不是很明显。研究了频漂对原子钟时域稳定性影响规律，还利用模拟数据进行了计算分析。验证了方法的有效性．  相似文献