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1.
郭彦  李建平 《大气科学》2012,36(2):385-396
针对预报量变化中存在受不同物理因子控制的不同时间尺度变率特征, 本文提出了分离时间尺度的统计降尺度模型。应用滤波方法, 将不同尺度的变率分量分开, 在各自对应的时间尺度上利用不同的大尺度气候因子分别建立降尺度模型。华北汛期 (7～8月) 降水具有年际变率和年代际变率, 本文以华北汛期降水为例利用分离时间尺度的统计降尺度模型进行预测研究。采用的预报因子来自海平面气压场、 500 hPa位势高度场、 850 hPa经向风场和海表温度场以及一些已知的大尺度气候指数。利用基于交叉检验的逐步回归法建立模型。结果表明, 年际尺度上, 华北汛期降水与前期6月赤道中东太平洋海温以及同期中国东部的低层经向风密切相关; 年代际尺度上, 在东印度洋—西太平洋暖池海温的作用下, 华北降水与前期6月西南印度洋海平面气压有同步变化关系。年际模型和年代际模型的结果相加得到对总降水量的降尺度结果。1991～2008年的独立检验中, 模型估计的降水和观测降水的相关系数是0.82, 平均均方根误差是14.8%。结合模式的回报资料, 利用降尺度模型对1991～2001年的华北汛期降水进行回报试验。相比于模式直接预测的降水, 降尺度模型预测的结果有明显改进。改进了模式预测中年际变率过小的问题, 与观测降水的相关系数由0.12提高到0.45。  相似文献   

2.
Using the techniques of empirical orthogonal function analysis and the change-point analysis to total summer rainfall from 60 weather observation stations, it was found that total summer (from June to September) rainfall in Korea has increased greatly since 1998. The increase level was higher in the season between Changma and late summer rainy season (from the end of July to early August) and in the season after late summer rainy season (after the early September). Among the reasons for increase of summer rainfall in Korea since 1998, the north-high and south-low pressure pattern formed around Korea drew attention. As northeasterlies and southeasterlies derived from these two pressure systems converged in Korea, rainfall and moisture convergence increased most in Korea of the East Asia regions (0–60°, 100–180° E). In addition, the atmosphere above Korea revealed that there were strong ascents from the ground to 200-hPa level with the warm air to 500-hPa level.  相似文献   

3.
利用1997—2015年吉林省春夏期(4—7月)逐日气象站地面观测资料,以气温、气压、相对湿度、水汽压、风速为协变量,建立各站点逐日降水量的基于自组织映射神经网络(Self-Organizing Maps,SOM)的统计预测模型;分析吉林省春夏期的主要天气模态,研究逐日降水和天气模态之间的关系,并基于此关系提出逐日降水量的蒙特卡罗模拟方法。结果表明:SOM对天气模态的分型质量较好,邻近天气模态的累积概率分布较相似,距离较远的天气模态累计概率分布差异较大。各天气模态下无降水的概率与日降水量区间宽度的相关系数为-0. 94,显著性水平小于0. 01。基于降水量累积概率分布,20种天气模态被划分成4类,并与降水易发程度和逐日降水量完全对应。在此基础上,对吉林省24个站点逐日降水量进行蒙特卡罗模拟,并进行预测性能分析。平均绝对误差(Mean Absolute Error,MAE)和均方根误差(Root Mean Square Error,RM SE)的中位数分别为3. 12 mm和6. 13 mm,SBrier和Ssig分别为0. 06和0. 51,站点的逐日降水量预测性能整体较好。MAE和RMSE分布呈现东南大西北小,去除降水自然变异差异的影响,所有站点的误差都较小; SBrier和Ssig没有明显的空间分布特征。  相似文献   

4.
Heavy rainfall events in austral summer are responsible for almost all the natural disasters in Southeast Brazil. They are mostly associated with two types of atmospheric perturbations: Cold Front (53%) and the South Atlantic Convergence Zone (47%). The important question of what synoptic characteristics distinguish a heavy rainfall event (HRE) from a normal rainfall event (NRE) is addressed in this study. Here, the evolutions of such characteristics are identified through the anomalies with respect to climatology of the composite fields of atmospheric variables. The anomalies associated with HRE are significantly more intense than those associated with NRE in all fundamental atmospheric variables such as outgoing long-wave radiation, sea-level pressure, 500-hPa geopotential, lower and upper tropospheric winds. The moisture flux convergence over Southeast Brazil in the HRE composites is 60% larger than in the NRE composites. The energetics calculations for the HRE that occurred in the beginning of February 1988 strongly suggest that the barotropic instability played an important role in the intensification of the perturbation. These results, especially the intensities of the wind, pressure anomalies, and the moisture convergence are useful for the meteorologists of the Southeast Brazil for forecasting heavy precipitation.  相似文献   

5.
Synoptic climatological patterns that produce anomalous wet conditions in central Australia during the period from September to April have been studied. The analysis was done by using observed daily rainfall data at a number of stations, wind and mean sea level pressure from the European Centre for Medium Range Weather Forecasts (ECMWF), Tropical Ocean and Global Atmosphere (TOGA) data from 1985 to 1991, and the CSIRO 9-level (CSIR09) global climate model (GCM) simulated data for 1 × CO2 and 2 × CO2 experiments. On the basis of rainfall values above 99.5 percentile in observed and simulated data, wet days have been selected to study the synoptic-scale weather systems that produce anomalous wet events in central Australia. As the vast majority of days in central Australia are dry, the same number of days with no rainfall for both observed and simulated conditions have been selected randomly. The observed synoptic climatological patterns have been compared with the results of the control simulation of CSIRO9. A comparison between CSIRO9 simulated synoptic patterns and observed synoptic patterns reveals that the model fairly well captures the synoptic climatological characteristics which produce anomalous wet and contrasting dry weather conditions during the period from September to April. Under enhanced greenhouse experiments, the main features of the synoptic patterns are intensified both for wet and dry conditions, which result in an increase in extreme weather conditions, an increase in rainfall intensity, a spatial expansion of the heavy rainfall region during wet days, and an expansion of the dry area during dry days. During anomalous wet conditions, the low pressure area is intensified, monsoonal winds and southeasterlies are strengthened and strong wind shear over tropical Australia is simulated. During this condition, the monsoon shear line moves poleward particularly over the Northern Territory. In contrast, during dry conditions, the anticyclonic circulation over the continent is strengthened.  相似文献   

6.
During the last decades, wildfires have received growing attention because of their major impact on the natural and anthropogenic infrastructures worldwide. The present paper focuses on investigating the relationship between the meteorological/climatological conditions and wildfires in Greece on a variety of temporal and spatial scales. This is performed through the identification of the mean surface temperature, the sea-level pressure, and the absolute humidity anomalies during wildfires at 26 meteorological stations covering both maritime and land environments in the Greek domain and the subsequent construction of the derived GIS surface contour maps. A case study analysis through composite anomaly maps of temperature, pressure, precipitable water, 500-hPa geopotential height, specific humidity, and vector wind is also performed. It is concluded that positive surface temperature, absolute/specific humidity, 500-hPa geopotential height, and vector wind anomalies are observed during wildfires while sea-level pressures are anomalously negative. Furthermore, western regions display lower magnitude anomalies compared to the more central and central-eastern regions during wildfires. The above meteorological/climatological findings in conjunction with medium range to seasonal climate forecasts could be used by wildfire risk managers to provide increased wildfire prediction accuracy and thus benefit many aspects of the natural and built environment.  相似文献   

7.
Shifts in the synoptic systems influencing southwest Western Australia   总被引：1，自引：1，他引：1  
A self-organising map is used to classify the winter circulation affecting southwest Western Australia (SWWA) into 20 different synoptic types. The changes in the frequency of these types and their links to observed rainfall are analysed to further understand the significant, prolonged, rainfall drop observed in this region since 1975. The temporal variability of the different synoptic types link well with the observed rainfall changes. The frequency of the troughs associated with wet conditions across SWWA has declined markedly since 1975 while the frequency of the synoptic types with high pressure over the continent, associated with dry conditions, has increased. Combining the frequency of the synoptic systems with the amount of observed rainfall allows a quantitative analysis of the rainfall decline. The decreased frequency of the troughs associated with very wet conditions accounts for half of the decline. Reductions in the amount of rainfall precipitating from each system also contribute to the decline. Large-scale circulation changes, including increases in the mean sea-level pressure and a decrease in the general baroclinicity of the region have been associated with the rainfall decline. These changes are suggested to be linked to increasing levels of greenhouse gases. Due to the strong link between the number of trough types and the rainfall over SWWA, the shifts in the frequency of these synoptic types could be used as a tool to assess simulated rainfall changes, particularly into the future.  相似文献   

8.
In order to systematically and visually understand well-known but qualitative and complex relationships between synoptic fields and heavy rainfall events in Kyushu Islands, southwestern Japan, during the BAIU season, these synoptic fields were classified using the Self-Organizing Map (SOM), which can convert complex non-linear features into simple two-dimensional relationships. It was assumed that the synoptic field patterns could be simply expressed by the spatial distribution of (1) wind components at the 850 hPa level and (2) precipitable water (PW) defined by the water vapor amount contained in a vertical column of the atmosphere. By the SOM algorithm and the clustering techniques of the U-matrix and the K-means, the synoptic fields could be divided into eight kinds of patterns (clusters). One of the clusters has the notable spatial features represented by a large PW content accompanied by strong wind components known as low-level jet (LLJ). The features of this cluster indicate a typical synoptic field pattern that frequently causes heavy rainfall in Kyushu during the rainy season.In addition, an independent data set was used for validating the performance of the trained SOM. The results indicated that the SOM could successfully extract heavy rainfall events related to typical synoptic field patterns of the BAIU season. Interestingly, one specific SOM unit was closely related to the occurrence of disastrous heavy rainfall events observed during both training and validation periods. From these results, the trained SOM showed good performance for identifying synoptic fields causing heavy rainfall also in the validation period. We conclude that the SOM technique may be an effective tool for classifying complicated non-linear synoptic fields and identifying heavy rainfall events to some degree.  相似文献   

9.
We compared the regional synoptic patterns and local meteorological conditions during persistent and non-persistent pollution events in Beijing using US NCEP–Department of Energy reanalysis outputs and observations from meteorological stations. The analysis focused on the impacts of high-frequency (period < 90 days) variations in meteorological conditions on persistent pollution events (those lasting for at least 3 days). Persistent pollution events tended to occur in association with slow-moving weather systems producing stagnant weather conditions, whereas rapidly moving weather systems caused a dramatic change in the local weather conditions so that the pollution event was short-lived. Although Beijing was under the influence of anomalous southerly winds in all four seasons during pollution events, notable differences were identified in the regional patterns of sea-level pressure and local anomalies in relative humidity among persistent pollution events in different seasons. A region of lower pressure was present to the north of Beijing in spring, fall, and winter, whereas regions of lower and higher pressures were observed northwest and southeast of Beijing, respectively, in summer. The relative humidity near Beijing was higher in fall and winter, but lower in spring and summer. These differences may explain the seasonal dependence of the relationship between air pollution and the local meteorological variables. Our analysis showed that the temperature inversion in the lower troposphere played an important part in the occurrence of air pollution under stagnant weather conditions. Some results from this study are based on a limited number of events and thus require validation using more data.  相似文献   

10.
This study describes warm spells in Northern Europe and determines the synoptic situations that cause their occurrence. In this article, a relatively warm day was defined as a day when the maximum temperature exceeded the 95th annual percentile, and a warm spell (WS) was considered to be a sequence of at least five relatively warm days. In the analysed multiannual period and within the investigated area, 24 (Kallax) to 53 (Oslo) WSs were observed. The occurrence of WSs was mainly connected with positive anomalies of sea level pressure and a 500-hPa isobaric surface, displaying the presence of high-pressure systems. This occurrence was also accompanied by positive T850 anomalies.  相似文献   

11.
The strength of the East Asian summer monsoon and associated rainfall has been linked to the western North Pacific subtropical high (WNPSH) and the lower-tropospheric low pressure system over continental East Asia (EA). In contrast to the large number of studies devoted to the WNPSH, little is known about the variability of the East Asian continental low. The present study delineates the East Asian continental low using 850-hPa geopotential height. Since the low is centered over northern EA (NEA), we refer to it as the NEA low (NEAL). We show that the intensity of the NEAL has large interannual variation, with a dominant period of 2–4 years. An enhanced NEAL exhibits a barotropic structure throughout the whole troposphere, which accelerates the summer-mean upper-tropospheric westerly jet and lower-tropospheric monsoon westerly to its south. We carefully identify the anomalous NEAL-induced rainfall anomalies by removal of the tropical heating effects. An enhanced NEAL not only increases rainfall locally in northern Northeast China, but also shifts the East Asian subtropical front northward, causing above-normal rainfall extending eastward from the Huai River valley across central-northern Japan and below-normal rainfall in South China. The northward shift of the East Asian subtropical front is attributed to the following processes without change in the WNPSH: an enhanced NEAL increases meridional pressure gradients and the monsoon westerly along the East Asian subtropical front, which in turn induces a cyclonic shear vorticity anomaly to its northern side. The associated Ekman pumping induces moisture flux convergence that shifts the East Asian subtropical front northward. In addition, the frequent occurrence of synoptic cut-off lows is found to be associated with an enhanced NEAL. Wave activity analysis indicates that the interannual intensity change of the NEAL is significantly associated with the extratropical Polar Eurasian teleconnection, in addition to the forcing of the tropical WNP heating.  相似文献   

12.
Over the past 40 years there have been significant changes in Australian rainfall with increases in the north-west and decreases in the east. Tropical cyclones (TCs) and other closed low pressure systems are important synoptic systems that provide a large proportion of Australia’s annual rainfall. This study examines the proportion of rainfall that can be attributed to TCs over the 1970–2009 period, and to TCs combined with other closed lows over the 1989–2009 period. The contribution of these systems to Australian rainfall trends is also analysed. Tropical cyclones are found to have little influence on rainfall trends over the full time period. However, when the more recent 21-year period is considered, TCs and other closed low pressure systems can partially explain the positive rainfall trend in the north-west. Similarly, other closed low pressure systems, such as cut-off lows and east coast lows, can explain some of the negative rainfall trend in the south-east. The contribution of TCs and other closed low pressure systems to rainfall trends in the north and south-east is found to be predominantly due to respective increases and decreases in the rainfall producing efficiency of the systems. An understanding of the influence of these synoptic systems on Australian rainfall in the current climate is vital for evaluating how Australia's water budget may change in future climates.  相似文献   

13.
In this study, we assess the prediction for May rainfall over southern China (SC) by using the NCEP CFSv2 outputs. Results show that the CFSv2 is able to depict the climatology of May rainfall and associated circulations. However, the model has a poor skill in predicting interannual variation due to its poor performance in capturing related anomalous circulations. In observation, the above-normal SC rainfall is associated with two anomalous anticyclones over the western tropical Pacific and northeastern China, respectively, with a low-pressure convergence in between. In the CFSv2, however, the anomalous circulations exhibit the patterns in response to the El Ni?o-Southern Oscillation (ENSO), demonstrating that the model overestimates the relationship between May SC rainfall and the ENSO. Because of the onset of the South China Sea monsoon, the atmospheric circulation in May over SC is more complex, so the prediction for May SC rainfall is more challenging. In this study, we establish a dynamic-statistical forecast model for May SC rainfall based on the relationship between the interannual variation of rainfall and large-scale ocean-atmosphere variables in the CFSv2. The sea surface temperature anomalies (SSTAs) in the northeastern Pacific and the central-eastern equatorial Pacific, and the 500-hPa geopotential height anomalies over western Siberia in previous April, which exert great influence on the SC rainfall in May, are chosen as predictors. Furthermore, multiple linear regression is employed between the predictors obtained from the CFSv2 and observed May SC rainfall. Both cross validation and independent test show that the hybrid model significantly improve the model''s skill in predicting the interannual variation of May SC rainfall by two months in advance.  相似文献   

14.
Based on the Tropical Rainfall Measuring Mission (TRMM) precipitation radar observations, wide con-vection (WC) is defi ned as contiguous convective echoes over 40 dBZ, accompanied with a near surface ...  相似文献   

15.
This study provides some guidance on the choice of predictor variables from both reanalysis products and the third version of the Canadian Coupled Global Climate Model (CGCM3) outputs for regression-based statistical downscaling models (SDMs) for climate change application in southern Québec (Canada). Twenty CGCM3 grid points and four surface observation sites in the study area were employed. Twenty-five deseasonalized predictors and four deseasonalized predictands (daily maximum and minimum temperatures, precipitation occurrence and wet day precipitation amount) were used to investigate correlation coefficients among predictors and to evaluate their predictive ability when used in a multiple linear regression (MLR) downscaling model. The basic statistical characteristics of vorticity at 1,000-, 850- and 500-hPa levels, U-component of velocity at 1,000-hPa level, temperature at 2?m (T 2) and wind direction at 1,000- and 500-hPa level of CGCM3 showed a larger difference with those of the NCEP reanalysis data. Therefore, those seven variables require high caution to be included as predictors in statistical downscaling models. Specific humidity at 1,000-, 850- and 500-hPa levels, geopotential height at 850- and 500-hPa levels and T 2 were the most sensitive predictors for future climate conditions (i.e. A1B and A2 emission scenarios). Specific humidity and geopotential height at different levels and T 2 were important explainable predictors for the daily temperatures. Mean sea level pressure, specific humidity, U and V components and divergence showed potential as predictors for daily precipitation. Spatial explained variance of MLRs between predictors of every different CGCM3 grid points and the four predictands showed large values at the CGCM3 grid points located near the observation sites, whereas relatively small values were shown at the CGCM3 grid points located more than 400?km from the sites. The explained variance of the downscaled predictands by predictors of three or four CGCM3 grid points located near the observation site produced 2–5% larger R-squares than those by predictors of the nearest grid point. The results illustrated that the use of predictors from more than one AOGCM grid points located near the observation site can increase the skill of the MLR downscaling models.  相似文献   

16.
Compared to the 50-year mean climatological value (1961–2010), the precipitation of middle-eastern Inner Mongolia exhibited a significant decrease during the past 10 years (2001–2010). To identify the climatic causes, a comprehensive investigation was conducted by inspecting climatic factors from this 50-year period, which appear to work together in connecting closely to the precipitation. Significant positive correlations with precipitation were found in sea level pressure (SLP) difference between the area of (30° N–20° S; 50–160° E) and the northeastern Pacific Ocean, between the Northern Atlantic and the northeastern Pacific Oceans, and sea surface temperature difference between the northeastern and northwestern Pacific in the previous year, while negative connections were found in the 500-hPa temperature difference between the Antarctic and the belt region around 60° S. During the period of 2001–2010, East Asia was prevailingly controlled by a huge high, which was regarded as one of unfavorable factors for producing rain or snow. Other factors were the enlarged 500 hPa temperature differences between the Antarctic and the zones around 60° S and the Equator, the negative SLP difference between the East Asia, northern Atlantic, and Pacific Oceans. Finally, the unique wind flows and associated moisture transports also played a key role in the precipitation reduction for the first decade of the twenty-first century.  相似文献   

17.
陈德花  陈创买  周学鸣  孙琼博  韦晋 《气象》2013,39(9):1190-1196
建立福建汛期降水量气候场的主分量逐步回归预测模型,通过预测福建汛期降水量气候场的主分量来实现对福建汛期降水量场的预测。选取北半球500 hPa高度场、太平洋海温场、北半球海平面气压场等含不同区域不同季节的诸多因子场的前若干主分量因子作为预测因子。计算分析了福建汛期降水场的主分量分布特征和分型特点。利用相关筛选和双重检验逐步回归方法,建立福建汛期降水场与多个因子场的关系,建立主分量的预测方程。通过对2012年福建汛期降水的预报,发现该模型对福建汛期降水的趋势和分布有较好的预测能力。  相似文献   

18.
The spatial and temporal variability of rainfall over Ethiopia during the summer (JJAS) season is studied using observations (both station and satellite based) and model simulation data. The simulation dataset is generated using the fourth version of the International Center for Theoretical Physics Regional Climate Model (RegCM4) for the period 1989–2005. Ethiopia is first divided into 12 homogeneous regions using criteria including rotated empirical orthogonal function (REOF), spatial correlation, seasonal cycles, and topographical features. Spatially averaged observed and simulated rainfall time series are then generated and analyzed for each region. Standardized rainfall anomalies of the observations and the simulated data are highly correlated over the northern, western, northeastern, central, and southwestern regions, while a weak correlation is found over the border regions of the country. The dominant modes of rainfall variability are identified using REOF, while time–frequency variations of different dominant modes are described by wavelet analysis. The first leading patterns of rainfall and upper wind (averaged between 100 and 300 hPa) are highly correlated and exhibit similar features between simulation and observations over the northern, western, southwestern, and eastern regions of Ethiopia. The second loading pattern of rainfall and the first loading pattern of low-level wind (averaged between 850 and 1,000 hPa) exhibit a dipole structure across the southwestern and northeastern regions of the country. The dominant signals in the first rotated principal component (RPC) of rainfall and upper level wind fields show a period of 4–5 and 2–3 years, while the dominant signals in the second RPC show a period of 2–3 years at a 0.05 significance level. The correlations of significant RPCs across gauge, gridded, and model rainfall fields with that of low and upper level winds show the presence of a significant relationship (correlation exceeding ～0.6). Overall, the RegCM4 shows a good performance in simulating the spatial and temporal variability of precipitation over Ethiopia.  相似文献   

19.
密云水库流域性暴雨的短期预报方法研究   总被引：1，自引：0，他引：1  
为了探索密云水库流域性暴雨的预报，着眼于影响暴雨的天气系统，从数值预报的解释应用入手，试验制作了密云水库流域性暴雨预报方法。通过整理1970-1993年24年间水库流域内20个水文站雨量资料，分析45个暴雨天气样本与历史天气形势和数值预报产品的关系，筛选出预报指标和预报因子，使用数值预报产品的解释应用方法，根据天气环流形势的分型，分别组建了6、7、8月每个月份的未来24小时暴雨天气预报方程。预报检验表明该预报方法是可信的，同时也表明客观划分环流型、筛选预报因子、恰当确定暴雨标准等是预报方法的关键。  相似文献   

20.
In this study, we investigate a long-term modulation in the relationship between Indian summer monsoon rainfall with the subsequent Australian summer monsoon rainfall. The two monsoon rainfall time series are significantly correlated at 0.3 at the 99 % confidence level. However, the relationship weakens during the 1932–1966 period, with the inter-monsoon correlation for the period falling below statistical significance. We find that this modulation is consistent with a breakdown of the typical El Niño-Southern Oscillation (ENSO) influence on sea surface temperature in the northern region of Australia, during this period. In addition, a change in the relative influences of ENSO and Indian Ocean Basin-wide Warming sea surface temperature anomalies on the Australian summer monsoon rainfall is also apparent across different time periods.  相似文献   

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