共查询到20条相似文献，搜索用时 15 毫秒
1.
采用中尺度数值模式MM5V2对1998年6月下旬发生在长江流域持续的暴雨过程进行分析研究。通过尺度分离与数值模拟对比试验，着重分析了暴雨过程中天气尺度与次天气尺度各物理量场的结构特征，提出本次暴雨过程形成的物理机制:天气尺度流场与水汽场为降水提供持续的远距离水汽输送通道，次天气尺度流场形成稳定的经向强辐合，为水汽的抬升与凝结提供动力条件；在有利的高、低空急流的配置下，暴雨区落在高空急流轴以南、低空急流轴以北；次天气尺度温度场下暖上冷的热力不稳定层结促进了热力不稳定的发展，促使暴雨增幅；特大暴雨发生地区上空的次天气尺度湿度的高值中心，有利于湿空气在上升运动中释放潜热，形成暴雨的反馈机制。数值试验分离模式初始场不同尺度系统信息，揭示了不同尺度系统在暴雨发生过程中的动力作用，没有中尺度系统的配合，仅有天气尺度系统信息，或只有次天气尺度系统信息，没有大尺度系统的配合，暴雨的强度及范围都将有所消减。分析及数值试验结果表明大暴雨是在天气尺度和次天气尺度系统的共同作用下才得以产生和维持的。 相似文献
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使用新建的强降水历史个例数据集、1981-2016年我国逐日降水量观测资料、2016年T639与ECMWF模式1~10 d的逐日降水量预报,采用经验正交函数展开（EOF）提炼出江淮地区强降水的典型模态,并运用场相似法对江淮地区强降水进行客观分型,分析强降水的环流演变;定量诊断型环流相似所得与实测环流和降水的对应关系。结果表明:江淮地区强降水可分为QⅠ,QⅡ和QⅢ 3种类型,其中,QⅠ型降水中心位于江淮中部,QⅡ型表现为降水北多南少,QⅢ型表现为降水中间少南北多的分布。强降水对应的前期至当日,各型降水对应在亚洲的中高纬度地区均有显著的环流异常,且环流演变存在明显不同;但各类型降水对应的系统移动速度缓慢,且到强降水发生日江淮地区处于西太平洋副热带高压西北侧低值系统的控制,有利于该地区强降水的发生。按环流相似依不同时效得到的强降水发生日环流与实际环流存在很好的相关。独立试验中,该文方法对25 mm降水的TS评分在各时效均高于模式预报,50 mm降水的TS评分在3 d以上时效的评分也均高于模式预报。 相似文献
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副高边缘暴雨的多普勒雷达回波特征 总被引：7，自引：4，他引：7
利用常规观测资料和多普勒雷达探测资料，对2003-2004年湖南省4次副高边缘暴雨的天气形势和雷达回波特征进行了分析研究。结果表明：4次暴雨过程的副高位置适当，高空有低槽，中低层有低空急流和低涡切变线，地面上有冷锋。在基本反射率图上，低槽暴雨有S-N向的窄带回波特征、冷式切变线暴雨有准W—E向的积层回波特征、暖式切变线有NE—SW向的积层回波特征，但每一次暴雨过程不尽相同。在多普勒速度图上常出现低空急流、冷暖平流、冷锋、逆风区以及高层大风核等特征，并常是几种特征同时出现，有利于强降水产生。 相似文献
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针对北京地区2012年7月21日(简称“7.21”过程)和2016年7月20日(简称“7.20”过程)极端特大暴雨中的短时强降水,对短时强降水实况、环流形势、地形影响及环境的动力、水汽和热力条件进行了分析,并结合较长时段的历史资料,从单点和区域角度对环境动力、水汽和潜在热力条件的极端性进行了对比分析。结果表明:(1)尽管两次过程中的短时强降水实况差异显著,但均出现在非常有利的天气形势下。(2)针对短时强降水环境的单点动力、水汽和热力条件对比显示,两次过程中的850 hPa动力抬升和整层可降水量(PWAT)均极端偏强,但抬升指数(LI)表征的热力条件差异差别巨大,2012年“7.21”过程中为偏强,2016年“7.20”过程中为偏弱。(3)针对长时间序列资料的标准化偏差异常(SD)显示,两次过程中850 hPa风场和PWAT的SD均超过了3σ,为极端偏强,LI表征的潜在热力条件方面,2012年“7.21”过程中低于-1σ,2016年“7.20”过程中与历史同期持平,表明热力条件的差异是导致两次极端暴雨过程中短时强降水强度巨大差异的重要原因。 相似文献
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R. Suppiah 《Climate Dynamics》1994,10(8):395-405
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
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A. K. Gu��ye Serge Janicot A. Niang S. Sawadogo Benjamin Sultan A. Diongue-Niang S. Thiria 《Climate Dynamics》2011,36(1-2):1-18
The aim of this work is to define over the period 1979?C2002 the main synoptic weather regimes relevant for understanding the daily variability of rainfall during the summer monsoon season over Senegal. ??Pure?? synoptic weather regimes are defined by removing the influence of seasonal and interannual time scales, in order to highlight the day by day variability of the atmospheric circulation. The Self-Organizing Maps (SOM) approach, a clustering methodology based on non-linear artificial neural network, is combined with a Hierarchical Ascendant Classification to compute these regimes. Nine weather regimes are identified using the mean sea level pressure and 850?hPa wind field as variables, and gathered into three classes. Two of these weather regimes represent the classical 3?C5-day African easterly waves with a mean wavelength of about 3,000?km. Three others are characterized by a modulation of the semi-permanent trough located along the western coast of West Africa and might be interpreted in terms of the 6?C9-day easterly waves. The last four weather regimes are characterized by a more or less strong north?Csouth dipole of circulation. They can be interpreted as a northward/southward displacement of the Saharan Heat Low for two of them, and a filling/deepening of this depression for the other two. The circulation patterns of all these nine weather regimes are very consistent with the associated anomaly patterns of precipitable water, mid-troposphere vertical velocity, outgoing longwave radiation, and finally rainfall. Rainfall distribution is also highlighted over the southwestern area of Senegal. 相似文献
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G. A. Efstathiou C. J. Lolis N. M. Zoumakis P. Kassomenos D. Melas 《Theoretical and Applied Climatology》2014,115(1-2):259-279
Raingauge data from four meteorological stations in Chalkidiki peninsula (Greece) were used to identify the characteristics of the synoptic circulation patterns associated with cold-season heavy rainfall events and corresponding flooding over the area. Precipitation climatology over the complex topography of Chalkidiki is characterized by limited annual rainfall, but in the occurrence of heavy rainfall episodes daily accumulations are exceptionally high with increased precipitation rates, leading often to severe flooding. Fifty-five cases of high daily accumulations for the period of 1997 to 2010, mostly observed during December and October, were classified into eight clusters by applying S-Mode Factor Analysis and Cluster Analysis to the ERA-Interim grid point reanalysis data. The results revealed that, in most cases, intense rainfall and flooding is produced by synoptic scale disturbances that generate and sustain cyclonic activity over south Italy, the Ionian, and less frequently over the Aegean Sea. In particular, the atmospheric circulation patterns associated with heavy rainfall are characterized by the presence of a southeasterly–easterly low-level humid flow over Chalkidiki in conjunction with the potentially unstable lower troposphere influenced by mid-level cyclonic vorticity advection and enhanced low-level convergence over the complex terrain. 相似文献
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This study examines southern African summer rainfall and tropical temperate troughs (TTTs) simulated with three versions of an atmospheric general circulation model differing only in the convection scheme. All three versions provide realistic simulations of key aspects of the summer (November–February) rainfall, such as the spatial distribution of total rainfall and the percentage of rainfall associated with TTTs. However, one version has a large bias in the onset of the rainy season. Results from self-organizing map (SOM) analysis on simulated daily precipitation data reveals that this is because the occurrence of TTTs is underestimated in November. This model bias is not related to westerly wind shear that provides favorable conditions for the development of TTTs. Rather, it is related to excessive upper level convergence and associated subsidence over southern Africa. Furthermore, the model versions are shown to be successful in capturing the observed drier (wetter) conditions over the southern African region during El Niño (La Niña) years. The SOM analysis reveals that nodes associated with TTTs in the southern (northern) part of the domain are observed less (more) often during El Niño years, while nodes associated with TTTs occur more frequently during La Niña years. Also, nodes associated with dry conditions over southern Africa are more (less) frequently observed during El Niño (La Niña) years. The models tend to perform better for La Niña events, because they are more successful in representing the observed frequency of different synoptic patterns. 相似文献
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闽中北短时暴雨概念模型 总被引：5，自引：1，他引：4
通过对福建中北部35个站1994～2001年97次暴雨过程的环流背景、影响系统等进行分析,将天气类型分为冷式切变(或槽)影响型、西南气流影响型、副高型(Ⅰ～Ⅱ型),归纳总结了各天气型的雷达回波源地、加强区域、路径、演变及降水特征,建立了天气图等常规资料与雷达回波资料相结合的闽中北短时暴雨3种概念模型。Ⅰ、Ⅱ型的降水强度总体相差不很大,有西南风急流比没有时降水强,Ⅱ型尤其明显,Ⅲ型降水强度最弱、持续时间最短。 相似文献
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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
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Impact of Horizontal Resolution and Cumulus Parameterization Scheme on the Simulation of Heavy Rainfall Events over the Korean Peninsula 总被引：1，自引：0，他引：1
In this paper, we present the results from high-resolution numerical simulations of three heavy rainfall events over the Korean Peninsula. The numerical results show that the prediction accuracy for heavy rainfall events improved as horizontal resolution increased. The fine-grid precipitation fields were much closer to the real precipitation fields in the case of large synoptic forcing over the Korean Peninsula. In the case of large convective available potential energy and weak synoptic forcing, it seems that even when using a high resolution, the models still showed poor performance in reproducing the observed high precipitation amounts. However, activation of the cumulus parameterization scheme in the intermediate resolution of 9 km, even at a grid spacing of 3 km, had a positive impact on the simulation of the heavy rainfall event. 相似文献
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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
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长江中下游一次非典型梅雨锋中尺度暴雨过程的分析研究 总被引：6，自引：0，他引：6
利用T10 6物理分析资料、地面与高空加密观测资料和TBB资料对 2 0 0 1年汛期一次非典型的梅雨锋中尺度暴雨过程进行天气学和动力学诊断分析 ,并与 1998年典型的梅雨锋中尺度暴雨过程作一些比较。首先分析了该次暴雨过程的大尺度背景场 ,发现与 1998年典型的梅雨锋形势不同的是 ,5 0 0hPa环流形势表现为贝加尔湖地区是阻塞高压 (阻高 ) ,南海季风涌形式不明显 ,南亚高压位置偏东南 ,高空辐散气流较弱。接着对该暴雨系统的结构进行诊断分析 ,揭示了该非典型梅雨锋中尺度暴雨系统的三维结构 ,包括各物理量如涡度、散度、假相当位温、水汽的通量以及湿位涡等的结构特征。分析表明 ,总体来说 ,该次暴雨过程的强度要比 1998年典型的梅雨锋暴雨要弱 ,相应的各物理量的三维结构与 1998年典型的梅雨锋中尺度暴雨系统的三维结构相比有明显差异。 相似文献
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Heavy rains frequently occur over the Serra do Mar, in the southeast coastal mountain region in Brazil, particularly during the summer season. These rains can cause landslides and loss of life. The objective of this work is to produce a synoptic climatology of heavy rainfall episodes of the period from November to April using 10-year reanalyses data. The identification of the synoptic pattern of these events should provide guidance to forecasters. The landslide events were mostly related to cold front passages and the South Atlantic Convergence Zone (SACZ). These systems differed from the climatology by exhibiting more intense characteristics for the frontal situations and a blocking circulation configuration for the SACZ situations. In both cases, the composite fields showed that the 250-hPa mass divergence was strikingly more intense than the climatology and had a preferred location in the 24 h prior to landslide events. Anomalies of this ten-year event climatology showed above-normal moisture anomalies, which are more evident in the SACZ than in the frontal cases. 相似文献
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Summary A numerical model is employed to study heavy rainfall events in complex terrain. The model uses a limited-fine-mesh grid and a nested grid, but does not utilize the same set of equations on both grids. Two similar, heavy rainfall cases are contrasted with each other and with a moderate precipitation case. Sensitivity experiments illustrate the effects of topography, synoptic forcing and diabatic heating on these episodes. Model results indicate that heavy rainfall in complex terrain requires a suitable superposition of mass, momentum and moisture fields in relation to the topography. It is the mass and momentum fields, however, which primarily control the location of heaviest precipitation. Synoptically similar events may be different in their underlying causes. The diabatic heating distribution may in some cases be essential to creating such episodes heavy rain.With 22 Figures 相似文献
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对流层高层偏北气流在梅雨暴雨中的作用 总被引：11，自引：0，他引：11
文中对江淮梅雨暴雨过程中的高低空流场特征及物理过程进行分析．结果表明：对流层上部青藏高原东侧常有高空偏北大风轴汇入南亚东风急流中．在这支强北风轴北端发现高空辐散和辐散的增长．亦即有利于低层辐合上升的持续、发展和加强;表明了低层西南急流与高空青藏高压东侧的偏北强风轴之间的次级环流圈,有利于梅雨暴雨的持续． 相似文献