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1.
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
2.
S. D. Bansod 《Theoretical and Applied Climatology》2005,82(3-4):143-152
Summary In this study the relationship between mid-tropospheric geopotential heights over the Northern Hemisphere (20° N to 90° N, around the globe) and Indian summer monsoon rainfall (ISMR: June to September total rainfall) have been examined. For this purpose, the monthly 500 hPa geopotential heights in a 2.5° lat./lon. grid over the Northern Hemisphere and the ISMR data for the period 1958 to 2003 have been used.The analysis demonstrates a dipole structure in the correlation pattern over the East Pacific Ocean in the month of January which intensifies in February and weakens in March.The average 500 hPa geopotential height over the eastern tropical Pacific Ocean during February (index one), has a significant positive relationship (r = 0.72) with the ISMR. In addition, the surface air temperature (SAT) anomaly over North-west Eurasia during January (index two) is found to be strongly related with the subsequent summer monsoon rainfall. These relationships are found to be consistent and robust during the period of analysis and these indices are found to be independent of each other.Hence, using index one and index two, a multiple linear regression model is developed for the prediction of the ISMR and the empirical relationships are verified on independent data. The forecast of the ISMR, using the above model, is found to be satisfactory.The dipole structure in the correlation pattern over the East Pacific region during February weakens once the ENSO (El-Nino and Southern Oscillation) events are excluded from the analysis. This suggests that the dipole type relationship between mid-tropospheric geopotential heights over the East Pacific Ocean and the ISMR may be a manifestation of the ENSO cycle. 相似文献
3.
一种局地非线性气候动力统计模型及其预报试验 总被引：1，自引：5，他引：1
根据反演建模理论，在引入一次样条函数的基础上，设计了一种局地非线性气候动力统计模型及其一整套反演方案。其实质是用逐段线性化的研究局地气候演化的非线性特征。作为初步试验，利用云南省18个测站1956年1月－1990年12月逐月温度距平和逐月雨量距平率的时间序列，反演得到一组近似描述云南省局地气候系统的非线性动力统计方程，应用反演获得的此非线性动力统计方程进行了云南省18个测站1991年1月－1994年12月逐月温度距平和逐月雨量距平率的预报试验。试验结果表明，温度距平和雨量距平率的拟合准确率分别约为78％和64％；温度距平和雨量距平率的外推预报准确率分别为75％和63％。表明此模型具有一定的拟合和预报能力，同时具有良好的稳定性。 相似文献
4.
海洋表面温度(Sea Surface Temperature,SST)具有非平稳、非线性的特征,直接将处理平稳数据序列的方法应用到非平稳非线性特征明显的序列上显然是不合适的,预测的误差将会很大。为了提高预测精度,更好地解决非平稳非线性序列预测的问题,本文以东北部太平洋(40°N~50°N、150°W~135°W)区域的月平均海洋表面距平温度为例,首先分别应用集合经验模态分解(EEMD)和互补集合经验模态分解(CEEMD)方法将SST分解为不同尺度的一系列模态分量(IMF),再运用BP(Back Propagation)神经网络模型对每一个模态分量进行分析预测,最后将各IMF预测结果进行重构得到SST的预测值。数值试验的结果表明,CEEMD分解精度比EEMD分解精度高,CEEMD提高了基于BP神经网络的预测精度。系列试验统计分析说明应用这种方法对SST的1年预测是有效的。 相似文献
5.
Summary The behavior of the Indian summer monsoon during the period 1979–1985 is examined with surface rainfall and infrared satellite data in order to determine how well the satellite measurements mimic the episodic rainfall processes. It is shown that equivalent-black-body-temperatures derived from satellite measured outgoing longwave radiation (OLR) estimates are reliable indicators for reproducing the timevariant zonal structure of monsoon rainfall over the Indian sub-continent—but only at preferred frequencies. The Indian summer monsoon is found to exhibit a distinct three episode cycle of active-break periods along two north-south aligned cross-sections; the first along the west Indian coast, the second through central India up to the plains of west Uttar Pradesh.We use the triplex behavior of the monsoon as a framework to describe individual monsoons from 1979 to 1985. This is done in terms of the initiation or phase, amplitude, duration, and propagation of the individual episodes. Cospectrum calculations between the rainfall and satellite temperature show that significant coherence is only associate with the frequencies corresponding to specific sub-seasonal fluctuating modes of the monsoon, i.e. 30–50 day and 10–20 day modes. The 30–50 day mode exhibits particularly strong coherence. It is shown how the behavior of the rainfall normals can be used to aid the calculation of a synthetic satellite temperature normal. Coherance at the 30–50 day mode in the co-spectrum of the departure time series is also strong; coherence at the 10–20 day mode is weaker but significant. This suggests that although satellite derived temperature is not a universal for rainfall, it could be used as a variable for monitoring the inra-annual behavior of the fluctuating rainfall modes of the monsoon.With 12 Figures 相似文献
6.
Summary An objective approach similar to the forward selection of independent variables in the multiple linear regression has been attempted to optimize the network of raingauges for the summer monsoon rainfall (June–September total) series (1871–1984) of India as well as its 29 selected meteorological subdivisions prepared involving the data of 306 raingauges. For the all-India monsoon rainfall series twenty seven gauges entered the selection whose mean showed the correlation coefficient (CC) of 0.9869. Keeping in view the difficulties of getting data from all the 306 gauges, 35 India Meteorological Department (IMD) gauges with mean showing CC of 0.9898 have been identified for updating this series. The constructed all-India monsoon rainfall series for the period 1871–1992 using 35 selected observations is presented. It was interesting to note that the set of 35 gauges selected for the monsoon total has shown equally promising results for the all-India monsoon monthly (June–September) as well as the annual rainfall series.For the 29 subdivisional monsoon rainfall series, however, in total 188 IMD-gauges (62% of the total of 306 gauges) entered the selection. For 17 subdivisions the CC exceeded 0.98, for 3 subdivisions it varied between 0.97 and 0.98, for 5 subdivisions between 0.96 and 0.97 and for the remaining 4 subdivisions between 0.90 and 0.94. They showed equally encouraging results for the monsoon monthly and annual rainfall series for the different subdivisions.Limitations and implications of the optimization technique are also briefly discussed.With 9 Figures 相似文献
7.
基于EMD方法的观测数据信息提取与预测研究 总被引：5，自引：1，他引：4
用统计方法作月、季尺度的短期气候乃至年际尺度的长期气候预测是当前气候预测业务的主要依据,在短时间内这种情况仍然不可能彻底改变。虽然数值预报模式的预测能力达到了7 d的时效,不过要积分到月、季尺度并实现短期气候预测还面临着重重困难。其根本原因是气候系统的混沌分量和非线性/非平稳性等因素在起作用。而现有气候预测的统计方法(主要包括经验统计、数理统计和物理统计等方法)的数学基础却忽略了这些特点,这是因为以现有的科学水平人们不得不假设时间序列是线性和平稳的。实际气候观测序列普遍具有层次性、非线性和非平稳性,这给建立预测方法带来了极大困难。文中构建了一个新的预测模型,即首先利用经验模态分解(em-pirical mode decomposition,EMD)方法将气候序列作平稳化处理,得到一系列平稳分量-本征模函数(intrinsic modefunction,IMF);其次,利用均生函数(mean generate function,MGF)模型获得各分量的初次预测值;最后,在最优子集回归(optimal subset regression,OSR)模型的基础上,通过直接或逐步拟合一部分预测值,构建两种预测方案达到提高预测能力的目的。典型气候序列的预测试验结果表明,具有平稳化的IMF分量,尤其是特征IMF分量有较高的可预测性,它对原序列趋势的预测有重要指示意义。大力开展气候系统机理和气候层次的研究,并建立相应的气候模式是未来发展趋势。该文是这方面的一个初步尝试,相信该模型能为气候预测(评估)开辟一条新的有效途径。 相似文献
8.
Summary Seven series of monthly pluviometric amounts, sometimes exceeding recording periods of 100 years and compiled by the Instituto Nacional de Meteorología (Spain), are used to study the irregularity of the pluviometric regime along the Spanish Mediterranean coast and nearby Atlantic
coast. First of all, three statistical functions (gamma, log-normal and a combination of Poisson and gamma distributions)
and moment-ratio diagrams are used to model the monthly and annual empirical distributions of precipitation amounts, each
distribution being tested by means of the Kolmogorov-Smirnov test. It is noteworthy that, whereas most of the monthly cases
require the gamma distribution, the pluviometric behaviour of the summer months is well described by the Poisson-gamma distribution.
Moreover, both the log-normal and the gamma distributions satisfactorily model empirical annual amounts. Consequently, rainfall
amounts are not identically distributed along a year for each gauge tested. Second, temporal trends deduced for annual and
seasonal amounts are computed and their statistical significance evaluated. The most notable fact is that, although some linear
trends are close to 1 mm/year, their significance levels exceed the assumed threshold value and, excepting the winter season
for Barcelona, they are considered non-significant from a statistical point of view. Finally, by again using monthly and annual
amounts, three temporal irregularity indexes are computed for each pluviometric series, the temporal disparity of the rainfall
patterns of the Mediterranean region being enhanced as a result. It addition to the temporal irregularity, a change with latitude
is observed both in the parameters of the statistical distributions and the temporal irregularity indexes for the rain gauges
analysed. The two most southerly rain gauges constitute a special case in comparison with the remaining stations, because
they also receive the Atlantic influences due to their proximity to this ocean.
Received February 25, 1999/Revised August 2, 1999 相似文献
9.
In urban drainage systems, knowledge of short-duration rainfall events can be considered as one of the most critical elements when their hydrological behaviour wants to be investigated. The temporal resolution of rainfall data usually available for practical applications is often lower than the data requested for the design procedures or mathematical models application, greatly affecting their reliability. Moreover, when high resolution rain gauges are available in the catchment, the registration period cannot be sufficiently long for obtaining practically usable statistical analyses. The present study proposes a method for estimating the distribution of sub-hourly extreme rainfalls at sites where data for time interval of interest do not exist, but rainfall data for longer duration are available. The proposed method is based on the “scale-invariance” (or “scaling”) theory whose concepts imply that statistical properties of the extreme rainfall processes for different temporal scales are self-related by a scale-changing operator involving only the scale ratio. The methodology is applied to extreme rainfall data from a rain gauge network within the metropolitan area of Palermo (Italy). Following the application, it is shown that the statistical properties of the rainfall series have a simple scaling property over the range of duration 10 min–24 h. A simple parsimonious analytical formulation for the DDF curves, which embodies the scaling behaviour, is presented. 相似文献
10.
Observations of accumulated precipitation are extremely valuable for effectively improving rainfall analysis and forecast. It is, however, difficult to use such observations directly through sequential assimilation methods, such as three-dimensional variational data assimilation or an Ensemble Kalman Filter. In this study, the authors illustrate a new approach that makes effective use of precipitation data to improve rainfall forecast. The new method directly obtains an optimal solution in a reduced space by fitting observations with historical time series generated by the model; it also avoids the implementation of tangent linear model and its adjoint. A lot of historical samples are produced as the ensemble of precipitation observations with the fully nonlinear forecast model. The results show that the new approach is capable of extracting information from precipitation observations to improve the analysis and forecast. This method provides comparable performance with the standard four- dimensional variational data assimilation at a much lower computational cost. 相似文献
11.
Peter Allerup 《Atmospheric Research》1996,42(1-4)
The aim of this paper is to present a rainfall generator which takes both spatial and temporal characteristics into account. The statistical model behind the generator is based on long-time experience with statistical analyses of empirical rainfall data and represents, therefore, a genuine theoretical point for simulating series of precipitation values. The sites of the recording gauges and the actual time (day, month, year etc.) enter a statistical model as systematic components for the prediction of expected rainfall in a two-way analysis of variance design. Beyond these systematic components, spatial correlations among the observations are still present in nature, a feature which is modelled also by the rainfall generator. 相似文献
12.
Desmond Manatsa Barnabas Chipindu Swadhin K. Behera 《Theoretical and Applied Climatology》2012,110(1-2):115-128
The decadal shift in the relationship between the Indian Ocean Dipole (IOD) and the East African rainfall is investigated using historical observational data. The climate system for equatorial East Africa (EEA) during the October to December (OND) ‘short rains’ season is characterised by spatiotemporal variations of the equatorial East African rainfall (EEAR). Therefore, the EEAR index is derived from the first principal component of the empirical orthogonal function analysis (EOF) of the EEA’s rainfall domain. The IOD, which has been linked with the EEAR in the previous studies, is the main climate mode controlling the tropical Indian Ocean during the OND period. It is usually represented by a dipole mode index based on the zonal gradient of SST anomalies in the tropical Indian Ocean. Therefore the climate modes, IOD and EEAR, are assumed to form a two-node network of subsystems which primarily control the climate of equatorial East Africa during the OND period. The collective behaviour of these climate modes is investigated through the examination of their representative indices for the period 1901 to 2009 using simple statistical techniques. The results suggest that the interaction between these two climate modes, which comprise the network, is not predominantly linear as previously assumed, but is characterised by shifts which are determined by the coupling and synchronisation processes of the tropical systems. In cases where synchronisation is preceded by an abrupt increase in coupling strength between the two subsystems, the established synchronous state is destroyed and a new climate state emerges such as in the years 1961 and 1997. This alteration in the regional climate is accompanied by notable changes in the regional rainfall and IOD variations. But in those events where synchronisation is followed by a sudden loss in coupling strength, the climate state is not disturbed and no shift in the climate of equatorial East Africa is noticed as in 1918. This climate shift mechanism appears to be consistent with the theory of synchronised chaos and is useful for long range predictions of the East African short rains. 相似文献
13.
B. Parthasarathy A. A. Munot D. R. Kothawale 《Theoretical and Applied Climatology》1994,49(4):217-224
Summary The Indian rainfall has often been used as a proxy data for the Asian monsoon as a whole for understanding the energy budget of the major circulation features and also used as an input parameter in estimating the other regional parameters. In view of this, a long homogeneous rainfall series of All-India (India taken as one unit) has been prepared based on a fixed and well distributed network of 306 raingauge stations over India by giving proper area-weightage. This paper contains a listing of All-India monthly, seasonal and annual homogeneous data series for the period 1871–1993. Some statistical details and long-term changes of the All-India monsoon rainfall have been discussed.With 4 Figures 相似文献
14.
Summary Rainfall anomaly patterns are obtained for the city of Barcelona from a statistical and a spectral point of view. The time
series consists of monthly rainfall amounts recorded over 128 years without interruption. Monthly positive and negative anomalies,
obtained as the difference between monthly amounts and monthly threshold values, are used for both types of analyses. The
threshold levels are derived form the deciles of theoretical monthly rainfall distributions, which have been previously modelled
by the gamma distribution. Positive and negative anomalies of the monthly rain amounts are investigated for these threshold
levels. The statistical analysis is applied to each decile considered, yielding empirical exponential laws that can be used
to forecast the cumulative number of episodes of consecutive months with either positive or negative anomalies equalling or
exceeding a fixed length. A set of linear laws, relating the expected rainfall amount cumulated during an episode of a fixed
length, is also deduced. It is worthy of mention that, independently of the decile considered, all the exponential and linear
laws have satisfactory regression coefficients. At the same time, it has also been possible to establish the evolution of
the coefficients of these laws with respect to the different deciles considered. The exponential laws for episodes of positive
and negative anomalies are the starting point, together with two hypotheses, to model probabilities of repeated long episodes
over an arbitrary number of years and their return periods in terms of the Poisson distribution model. Moreover, power spectra
are derived for anomalies relative to the 50% decile at monthly and seasonal scale. The spectral estimates obtained are then
compared with theoretical spectra deduced from possible Markovian or random behaviour of the time series of anomalies. Finally,
the significant spectral peaks are discussed and compared with other significant spectral components deduced for some areas
of the Mediterranean domain.
Received November 11, 1999 Revised February 28, 2000 相似文献
15.
This paper compares the performance of seven disaggregation models, based on various approaches and/or concepts, for the generation of 10-min time step rainfall series from hourly rainfall series. The so-called constant disaggregation model and a linear model based on the external temporal pattern of rainfall are first considered. The other models are stochastic: the first ones are based on a given probability density function applying for the 10-min rainfall amounts of the hour to disaggregate. This probability density function is either uniform or derived from the external temporal pattern of rainfall. The other stochastic models are scaling models using canonical or microcanonical multiplicative random cascades. The comparison of the models is based on their ability to reproduce some important statistical characteristics of the observed time series: variance, skewness coefficient, wet/dry properties of 10-min rainfall amounts; rainfall amounts quantiles for different return periods; autocorrelation of 10-min rainfall amounts. A continuous hydrological simulation is next applied to produce for each generated rainfall series a continuous discharge series used afterwards for a retention design. The ability of the different disaggregation models to produce rainfall time series resulting in the same retention design than the one obtained with the observed rainfall series is finally analysed. Deterministic models as well as simpler stochastic models have rather bad performances when compared to the others. Because it is non-conservative, the model based on a microcanonical random cascade performs also very poorly. It significantly overestimates all studied statistics. Models based on microcanonical random cascades achieve the best performance. They perform reasonably well for the reproduction of rainfall statistics and almost perfectly for the reproduction of runoff and storage design variables. Results finally highlight the interest of including in the disaggregation scheme information related to the external temporal pattern of rainfall. 相似文献
16.
Skill, reproducibility and potential predictability of the West African monsoon in coupled GCMs 总被引：1，自引：1，他引：0
In the framework of the ENSEMBLES FP6 project, an ensemble prediction system based on five different state-of-the-art European
coupled models has been developed. This study evaluates the performance of these models for forecasting the West African monsoon
(WAM) at the monthly time scale. From simulations started the 1 May of each year and covering the period 1991–2001, the reproducibility
and potential predictability (PP) of key parameters of the WAM—rainfall, zonal and meridional wind at four levels from the
surface to 200 hPa, and specific humidity, from July to September—are assessed. The Sahelian rainfall mode of variability
is not accurately reproduced contrary to the Guinean rainfall one: the correlation between observations (from CMAP) and the
multi-model ensemble mean is 0.17 and 0.55, respectively. For the Sahelian mode, the correlation is consistent with a low
PP of about ~6%. The PP of the Guinean mode is higher, ~44% suggesting a stronger forcing of the sea surface temperature on
rainfall variability over this region. Parameters relative to the atmospheric dynamics are on average much more skillful and
reproducible than rainfall. Among them, the first mode of variability of the zonal wind at 200 hPa that depicts the Tropical
Easterly Jet, is correlated at 0.79 with its “observed” counterpart (from the NCEP/DOE2 reanalyses) and has a PP of 39%. Moreover,
models reproduce the correlations between all the atmospheric dynamics parameters and the Sahelian rainfall in a satisfactory
way. In that context, a statistical adaptation of the atmospheric dynamic forecasts, using a linear regression model with
the leading principal components of the atmospheric dynamical parameters studied, leads to moderate receiver operating characteristic
area under the curve and correlation skill scores for the Sahelian rainfall. These scores are however much higher than those
obtained using the modelled rainfall. 相似文献
17.
利用1951—2006年NCEP/NCAR再分析资料,采用EOF（empirical orthogonal function,经验正交函数）展开方法提取了南太平洋12—2月海表温度变化的主要模态,其第一模态反映了ENSO（El Nino-Southern Oscillation）的信号,周期为3～5a;第二模态与南半球环状模（Southern-Hemi-sphere annual mode,SAM）相联系,周期为准两年。结果表明,南太平洋EOF1时间序列处于正（负）相位时华北地区后期5月多（少）雨,同时注意到南、北太平洋EOF1对中国5月降水的影响区域基本一致。南太平洋EOF2时间序列处于正（负）相位时江南地区的夏季平均降水减少（增多）。去掉EOF1和EOF2的线性趋势后,这种显著相关仍然存在,只是显著相关区域有所缩小。利用南、北太平洋EOF1时间序列作为预报因子,建立回归预报方程,可为预测中国华北地区5月降水提供依据 相似文献
18.
In this paper, the characteristics of the long-term precipitation series at Athens (1858–1985) have been statistically analyzed. This study covers both the history and the analysis of the data. The ten-year mean amounts, the monthly and annual amounts averaged over the intervals 1858–1890, 1891–1985, 1951–1980, 1858–1985, the mean number of hours of precipitation and the precipitation intensity are given. The analysis of long-term time series of climatic data (in particular precipitation) is a useful tool for the study of past climate. Different statistical techniques are used in order to depict monthly, seasonal and annual variations, as well as trends, periodicities and recurrence intervals of the amount, intensity and number of precipitation days. The analysis reveals many interesting characteristics. These characteristics of the precipitation regime are extended to a time scale from seasonal variation to a semi-secular trend. The study of such long-term series may be helpful not only in practical applications of rainfall, but also for explaining the possible physical or anthropogenic mechanisms of climatic fluctuations and tendencies. The series of precipitation at Athens is one of the longest in south-eastern Europe. 相似文献
19.
Fotis Fotopoulos Christos Makropoulos Maria A. Mimikou 《Theoretical and Applied Climatology》2011,104(3-4):403-414
An extensive validation of two of the most popular and recently upgraded satellite rainfall products, 3B42 and 3B42RT, was performed over the Evros catchment in southeastern Europe using data recorded from January 2000 to April 2009. For conducting this validation study, the Climate Prediction Center's (CPC) ground data were used. The satellite data products were aggregated to daily time series, remapped to spatial resolution of 0.5°, validated against CPC, and intercompared using a variety of statistical indices and coefficients. After the validation process, all three data sets (CPC, 3B42, and 3B42RT) were separately fed in a statistical rainfall?Crunoff model, in order to predict the five major recorded flood events which occurred in the Evros catchment during the last decade. It has been found that post-calibration with ground data, which is present only in 3B42 product, is a necessity for operational flood forecasting and similar studies conducted in areas at mid-latitudes. Knowledge of rainfall events with small intensities is crucial for estimating the total rainfall height and drastically improves the skill of the satellite product. 相似文献
20.
Reconstruction of Nineteenth Century Summer Temperatures in Norway by Proxy Data from Farmers'Diaries 总被引：2，自引：0，他引：2
P.Ø. Nordli 《Climatic change》2001,48(1):201-218
Proxy data from five farmers; diaries in the Møre, Dovre and Trøndelag regions in central Norway were used for climatic reconstruction purposes. The method chosen was "simple linear regression analysis" with the start of the grain harvest (barley or oats) as predictor and summer temperature (May – August) as predictand. Overlapping periods with modern instrumental observations (starting 1858 or later) were used for calibration of the model. The model was tested on independent data by establishing the regression on one half of the overlapping period and applying the regression on the other half. The standard deviation in the residuals varied from 0.3°C to 0.7°C and the biases of the mean values from –0.3°C to +0.3°C. Climatic reconstructions were established for the early- and mid-nineteenth century summer temperature, i.e. during the last part of what has come to be regarded as the "Little Ice Age", in this article considered to end around 1880.By use of the proxy data model, huge inhomogeneities of the "classical" Trondheim series were detected, the early nineteenth century part of the series evidently being too warm. The inhomogeneity was removed by use of adjustment terms. The adjusted series indicates that in the Trondheim region the summer temperature during the last part of the "Little Ice Age" phase was about 1°C lower than the latest 60 years. This is in serious contradiction to the classical Trondheim series. 相似文献