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中国春季沙尘暴的趋势变化及年代际变化 总被引:8,自引:2,他引:6
利用奇异谱分析等方法,对北疆等7个区春季1960—2000年的沙尘暴日数的趋势和周期进行了初步分析,结果表明:除北疆区未表现出明显的趋势外,南疆区等其它6个区春季沙尘暴日数变化总的趋势是减少的,都是在20世纪60年代和70年代偏多,80年代沙尘暴开始减少,90年代最少;其中南疆区、河西区和东北区的年代际变化最为明显,大约是80年代初开始沙尘暴明显减少,其它几个区的年代际变化不是很明显。南疆等大部分地区春季的沙尘暴日数在70年代末和80年代初发生了由多到少的转变,基本上与北半球大气环流的调整同步,这可能是对大气环流调整的响应;除西藏区有7.7年的周期外,其它6个区的周期基本上都集中在准2年和5~6年两个周期段。 相似文献
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Long‐term variations and temporal scaling of hydroclimatic time series with focus on the German part of the Elbe River Basin 下载免费PDF全文
Long‐term variations and temporal scaling of mean monthly time series of river flow, precipitation, temperature, relative humidity, air pressure, duration of bright sunshine, degree of cloud cover, short wave radiation, wind speed and potential evaporation within or in vicinity of the German part of the Elbe River Basin are analyzed. Statistically significant correlations between the 2–15 year scale‐averaged wavelet spectra of the hydroclimatic variables and the North Atlantic Oscillation‐ and Arctic Oscillation index are found which suggests that such long‐term patterns in hydroclimatic time series are externally forced. The Hurst parameter estimates (H) based on the Detrended Fluctuation Analysis (DFA) indicate persistence for discharge, precipitation, wind speed, air pressure and the degree of cloud cover, all having an annual cycle and a broad low‐frequency distribution. Also, DFA H parameter estimates are higher for discharge than for precipitation. The major long‐term quasi‐periodic variability modes of precipitation detected using Singular Spectrum Analysis coincide with those detected in the discharge time series. Upon subtraction of these low‐frequency quasi‐periodic modes, the DFA H parameter estimates suggest absence of the persistence for both precipitation and discharge. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Based on the NCEP (National Centers for Environmental Prediction) data, the relationship between the Sea Surface Temperature
Anomalies (SSTAs) in the North Pacific and the atmospheric circulation anomalies in January 2008 is analyzed in this study.
The SSTA mode most correlated with the Geopotential Height anomalies (GHAs) in January 2008 in the North Pacific exhibited
a basin-wide horseshoe pattern with a warm center in November 2007. This persistent SSTA pattern would induce positive GHAs
in the Aleutian Low area and East Asia and the northward extension of the West Pacific Subtropical High in January 2008 by
maximum diabatic heating in the atmosphere over the Kuroshio Oyashio Extension (KOE) area, leading to the occurence of the
circumpolar trough-ridge wave train anomaly in January 2008. 相似文献
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本文研究并建立了一种模拟各向异性地层中三维电性异常体电磁响应的积分方程算法.首先讨论了并矢Green函数及其相关积分的计算,将水平层状各向异性地层中的电场并矢Green函数分解成含有奇异项的直达波与非奇异的来自各个层界面的反射和透射波两个部分,再应用等效体积单元和表面积分技术对积分方程的奇异核进行离散化处理以便提高离散方程的精度.然后为了节省计算机内存以及计算时间,引入基于Krylov子空间的迭代算法求解积分方程的离散化矩阵方程.最后通过与现有文献中的结果作对比从而检验了所述算法的有效性,并结合具体算例考察分析了地层的各向异性对三维电性异常体电磁响应的影响特征和规律. 相似文献
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简要介绍了地面核磁共振找水的正演理论方法,采用高斯求积并结合连分式展开的方法对核磁共振核函数中包含双重贝塞尔函数的积分核进行了数值积分,进而计算出精度较高的核函数值,在此基础之上,讨论了导电性对地面核磁共振信号的影响.基于奇异值分解算法,对核磁共振找水理论模型进行了反演研究,在不导电的情况下,重构出了比较理想的含水率分布.总结并改进了模拟退火算法,用改进的模拟退火算法分别对覆盖层高阻和导电条件下的核磁共振人工合成数据进行了反演,试验结果表明,利用改进的模拟退火算法反演地面核磁共振是可行的,而且反演结果较稳定,收敛速度较快. 相似文献
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A significant practical problem with the pilot point method is to choose the location of the pilot points. We present a method that is intended to relieve the modeler from much of this responsibility. The basic idea is that a very large number of pilot points are distributed more or less uniformly over the model area. Singular value decomposition (SVD) of the (possibly weighted) sensitivity matrix of the pilot point based model produces eigenvectors of which we pick a small number corresponding to significant eigenvalues. Super parameters are defined as factors through which parameter combinations corresponding to the chosen eigenvectors are multiplied to obtain the pilot point values. The model can thus be transformed from having many-pilot-point parameters to having a few super parameters that can be estimated by nonlinear regression on the basis of the available observations. (This technique can be used for any highly parameterized groundwater model, not only for models parameterized by the pilot point method.) 相似文献
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A deterministic method for sensitivity analysis is developed and applied to a mathematical model for the simulation of flow in porous media. The method is based on the singular value decomposition (SVD) of the Jacobian matrix of the model. It is a local approach to sensitivity analysis providing a hierarchical classification of the directions in both the input space and of those in the output space reflecting the degree of sensitiveness of the latter to the former. Its low computational cost, in comparison with that of statistical approaches, allows the study of the variability of the results of the sensitivity analysis due to the variations of the input parameters of the model, and thus it can provide a quality criterion for the validity of more classical probabilistic global approaches. For the example treated here, however, this variability is weak, and deterministic and statistical methods yield similar sensitivity results. 相似文献