共查询到20条相似文献，搜索用时 195 毫秒
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一.经验正交函数分析为了客观和定量地测定热带风暴和台风(TSTy)的位移,本文对163个台风样本中的12个纬向位移和12个经向位移(相对于163个样本平均值和距平)进行了经验正交函数分析。设 F 是一个24行163列的资料矩阵,其中(?)表示第 n 个热带气旋和台风的纬向和 相似文献
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经验正交函数(简称EOFs)展开气象场或对多气象指标进行主成分分析,已成为表示天气气候资料信息特征的有力工具。EOF's原是一种定量描述实际场序列(向量空间)主要信息特征的函数逼近方法。引入随机观点后,这种展开方法不仅是纯粹的函数逼近问题,而且是对具有随机噪声的信息场提取信息特征,排除随机干扰的统计学方法。事实上,任何一种气象要素场都可视为附加随机扰动的随机场(如气温场、气压场 相似文献
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本文用经验正交函数法分析了南京气温垂直分布的统计特征及地面气温对正交展开的影响,提出利用经验正交函数展开法进行大气温度廓线遥感反演的一种改进方法。 相似文献
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经验正交函数展开精度的稳定性研究 总被引：7，自引：3，他引：7
在文献[1]中,我们已从理论和数值模拟两个方面研究了用经验正交函数作基函数缩减气候数值模式自由度的可行性与有效性。用理论模型作数值试验的结果是令人满意的,应用于实际气候数值模拟,一个还需考虑的关键问题是大气外强迫等各种因子变化允许的范围内,对实际资料作EOF展开的稳定性问题。本文分别用1951—1984年500 hPa月平均高度距平场资料,1966—1975年500 hPa候平均高度距平场资料,1965—1978年夏季500 hPa逐日高度距平场资料作EOF展开,并提出了经验正交函数展开精度稳定性的判断方法,旨在证明实际资料EOF展开在大气外强迫等各种因子变化的允许范围内是稳定的,以便为我们用实际资料的经验正交函数作基函数建立一个合理的简化动力模型提供坚实的资料基础。 相似文献
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辐射传输方程的一个改进算法 总被引：3，自引：1，他引：3
本文研究了散射相函数的有限项的勒让德展开对于求解辐射传输方程的误差效应,提出了一个改进算法.理论分析和数值试验的结果都表明,多次散射分量和辐射通量远比一次散射分量对相函数的展开误差不敏感.只要用正确的相函数修正一次散射分量、就能在较少项的相函数勒让德展开下得到精确的辐射强度解,从而大大提高了计算速度,对于小于1的光学厚度,计算时间可减少五分之四. 相似文献
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梅雨天气形势的经验正交函数分析 总被引：2，自引：1，他引：2
众所周知,梅雨天气形势与副热带高压位置和强度的季节性变动关系密切。本文应用经验正交函数展开形势场的方法分析1982年6—7月副热带高压的变动和晚梅天气形势的特点。结合卫星云图等分析,对江淮两次梅雨期的暴雨成因作了探讨。 1.分析资料及其经验正交函数展开 为了分析副热带高压的变动和江淮流域梅雨天气,在20°—40°N和105°—125°E范围内选取有连续记录的48个测站的资料,从1982年6月1日至7月18日各站08时的500hPa’高度和温度作为原 相似文献
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本文在经验正交函数(EOF)展开的基础上,提出了一种预报月平均气温的EOF迭代方案,试验结果表明,本方法对六个月以内的日平均气温有较好预报能力。 相似文献
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N. M. Datsenko N. N. Ivashchenko D. M. Sonechkin Q. Chun B. Yang 《Russian Meteorology and Hydrology》2011,36(4):239-243
The characteristics of spatiotemporal variability of surface air temperature anomaly fields in China are computed from the
data of instrumental observations carried out from 1907 to 2000. The fields are represented by their empirical orthogonal
function expansion. The temporal variations of the coefficients of this expansion are considered at the scale range from one
month to five years. It turned out that both the orthogonal function structure and the type of the temporal variability of
expansion coefficients in China differ from those in Northern Eurasia. Investigating the current climate warming in China,
it is enough to consider the first two empirical orthogonal functions of temperature fields only. The characteristic time
of the existence of temperature anomalies described by these functions is almost the same as that of the temperature anomalies
in Northern Eurasia described by the first empirical orthogonal function of the respective fields. 相似文献
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This study describes a method of calculating the mean squared error (MSE) incurred when estimating the spherical harmonic
coefficients of a climatological field that is sampled at a small network of points. The method can also be applied to the
coefficients of any other set of orthonormal basis functions that are defined on the sphere. It, therefore, provides a formalism
that can be applied in a variety of contexts, such as in climate change detection, where inferences are attempted about fingerprint
coefficients that are imperfectly estimated from observational data. By incorporating the fingerprint as part of a set of
basis functions, the methodology can be used to estimate the sampling error in the fingerprint coefficient. The MSE is expressed
in terms of the spherical harmonics (or other orthonormal expansion) of the empirical orthogonal functions (EOFs), the locations
of the points in the network and a set of weights that are applied at these points. The weights are optimised by minimising
the expected MSE. The method is applied to a number of network configurations using monthly-mean screen temperature and 500 mb
height simulated by the Canadian Climate Centre 2nd generation general circulation model in an ensemble of six 10-year simulations.
In comparison with uniform weighting, optimal weighting can reduce the MSE by an order of magnitude or more for some spherical
harmonic coefficients and some network configurations. Also, the MSEs vary seasonally for each network. In particular, the
relative MSE of low order spherical harmonic coefficients is found to be larger in DJF than in JJA. We demonstrate how MSEs
improve with increasing network density and identify graphically, the coefficients that can be estimated reliably with each
network configuration.
Received: 19 April 1996 / Accepted: 10 April 1997 相似文献
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A statistical method of reconstruction of winter and semiannual precipitation totals at the network of weather stations in Europe is considered. The sea-level pressure field in the North Atlantic is used as a predictor for precipitation reconstruction. The stability of pressure field filtration is studied from empirical orthogonal functions (EOF) with the help of informative parameter of the pressure vector components. Results of numerical experiments are presented. 相似文献
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基于NASA遥感系统提供的2003~2015年全球高分辨率海表温度资料,应用经验正交函数分析、时滞相关分析等方法,对北太平洋冬季黑潮延伸体区海温异常特征及其与热带海表温度的可能关系进行了初步分析。研究发现,冬季延伸体区的海温异常主要表现为两类结构特征,其一为上游区域发展型,包括海盆尺度一致性变化的季节模态和纬向反位相的收缩型结构;其二为纬向延展型,包括分叉东扩结构和通道东扩结构,且该两结构型在2010年前反位相,使得2006年前暖异常东扩路径基本控制在36°N以南,其后至2010年期间,暖异常东扩路径偏北,而2010年后结构型转为同位相,暖异常东扩路径偏北。分叉东扩结构表现为与热带海温变化紧密相关,进一步的时滞相关分析与合成分析表明,热带太平洋不同地区对中纬度海温分叉东扩的影响存在差异,Ni?o3区海温异常超前延伸体区分叉东扩模态约1~2个月,而Ni?o3.4区及Ni?o4区则与延伸体区海温分叉东扩保持前后各约3个月的宽谱同期负相关,或可表明El Ni?o的东部型和中部型对中纬度延伸体暖流分叉东扩存在超前和同期相关影响,且中部型影响更显著。 相似文献
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神经网络模型预报湖北汛期降水量的应用研究 总被引：18，自引：1，他引：18
使用人工神经网络方法建立了湖北省汛期 (6～ 8月 )总降水量的短期气候预测模型 ,该神经网络模型的输入是汛期前期 (2～ 4月 )的北半球月平均 5 0 0 h Pa高度场、海平面气压场和太平洋海温场的扩展自然正交展开 (EEOF)的前几个主要模态的时间系数 ,输出了湖北汛期降水场的自然正交展开 (EOF)的前 2个主要模态的时间系数。41 a历史资料的交叉检验表明 :样本试验的预报技巧评分平均为 0 .2 4 6 ,虽然该模型对各年的预报效果仍存在一定的不稳定性 ,但它可为湖北汛期降水的短期气候预测提供一种具有明显统计预报正技巧的预报方法 相似文献
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Summary The spatial and temporal variability of winter precipitation and its links to the large-scale atmospheric circulation patterns in Romania are examined. The data set is composed of observed rainfall at 30 meteorological stations during the 1961–1996 period. The large-scale field is represented by the observed geopotential height at 500 hPa (Z500) over the same period, covering the latitudinal belt between 20° N–90° N (resolution 2.5°×2.5°).The Standard Normal Homogeneity Test (SNHT) is applied to detect inhomogeneities in the data, and the Mann-Kendall and Pettitt non-parametric tests are used in order to identify trends and change points in the winter precipitation time series. The empirical orthogonal functions (EOF) technique is used for data reduction in order to highlight the basic patterns of rainfall variability in Romania. The covariance map between precipitation EOF time series (PCs) and the Z500 field, as well as the correlation coefficients between the PCs and circulation indices are calculated in order to identify the influence of large-scale circulation patterns on winter precipitation in Romania.A significant decreasing trend is identified in winter precipitation with a downward shift in winter 1969/1970, most significant from a statistical point of view in the extra-Carpathian region. This change seems to be real since the SNHT test does not reveal any inhomogeneity during the period tested. Significant relationships are found between winter precipitation variability in Romania and the large-scale circulation pattern, such as the North Atlantic Oscillation and the blocking phenomenon in the Atlantic-European sector. The positive phase of the NAO and the reduction in blocking activity could be one of the causes of the decrease in winter precipitation in Romania. 相似文献
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Representations of inverse covariances by differential operators 总被引：2，自引：1，他引：1
In the cost function of three- or four-dimensional variational data assimilation, each term is weighted by the inverse of its associated error covariance matrix and the background error covariance matrix is usually much larger than the other covariance matrices. Although the background error covariances are traditionally normalized and parameterized by simple smooth homogeneous correlation functions, the covariance matrices constructed from these correlation functions are often too large to be inverted or even manipulated. It is thus desirable to find direct representations of the inverses of background error correlations. This problem is studied in this paper. In particular, it is shown that the background term can be written into f dx|Dv(x)|^2, that is, a squared L2 norm of a vector differential operator D, called the D-operator, applied to the field of analysis increment v(x). For autoregressive correlation functions, the D-operators are of finite orders. For Gaussian correlation functions, the D-operators are of infinite order. For practical applications, the Gaussian D-operators must be truncated to finite orders. The truncation errors are found to be small even when the Gaussian D-operators are truncated to low orders. With a truncated D-operator, the background term can be easily constructed with neither inversion nor direct calculation of the covariance matrix. D-operators are also derived for non-Gaussian correlations and transformed into non-isotropic forms. 相似文献
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Climate Dynamics - The second empirical orthogonal function mode (EOF2) of winter surface air temperature (SAT) over 0°–180° E, 40°–90° N during 1979–2005 is... 相似文献
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The horizontal and vertical structure of the 3–5-day and 6–9-day easterly waves over West Africa and tropical Atlantic are
investigated. NCEP/NCAR reanalyses are used for the period 1979–1995 to produce a 17-year climatology of both 3–5-day and
6–9-day easterly waves. Composite patterns of convection, wind, temperature and vertical velocity are analysed with respect
to the following: the modulation by 3–5-day and 6–9-day wave regimes; the contrasts between the ITCZ (5°N–10°N) and the Sahelo-Saharan
band (15°N–20°N); the difference between land and ocean, and seasonal variations. Similarities and differences in the characteristics
of the two wave regimes are identified.
Received: 18 August 1999 / Accepted: 14 March 2001 相似文献
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采用EOF时空分解、小波频牢分解和最小二乘支持向量机（LS-SVM）交叉互补方法,建立夏季500 hPa位势高度场的预测模型,用以描绘和表述副热带高压形势场的形态和变化。首先用经验正交函数分解（EOF）方法将NCEP/NCAR再分析资料500 hPa位势高度场序列分解为彼此正交的特征向量及其对应时间系数,随后提取前15个主要特征向龟的时间系数（方差贡献96.2%）,采用小波分解方法将其分解为相对简单的带通信号,再利用LS-SVM方法建立各分量信号的预测模型,最后通过小波时频分量重构和EOF时空重构,得到500hPa位势高度场的预测结果以及副热带高压形势场的预测。通过对预测模型的试验情况和分析对比,结果表明:基于上述思想提出的算法模型能较为准确地描述500 hPa位势高度场的形态分布并预测1~7 d的副热带高压活动,对10~15 d的副热带高压活动预测结果也有参考意义。 相似文献