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1.
In this study,power spectral analysis and bandpass filtering of daily meteorological fields are performed to explore the roles of synoptic to quasi-monthly disturbances in influencing the generation of pre-summer heavy rainfall over South China.Two heavy rainfall episodes are selected during the months of April-June 2008-15,which represent the collaboration between the synoptic and quasi-biweekly disturbances and the synoptic and quasi-monthly disturbances,respectively.Results show that the first heavy rainfall episode takes place in a southwesterly anomalous flow associated with an anticyclonic anomaly over the South China Sea(SCS)at the quasi-biweekly scale with 15.1%variance contributions,and at the synoptic scale in a convergence zone between southwesterly and northeasterly anomalous flows associated with a southeastward-moving anticyclonic anomaly on the leeside of the Yungui Plateau and an eastwardpropagating anticyclonic anomaly from higher latitudes with 35.2%variance contribution.In contrast,the second heavy rainfall episode takes place in southwest-to-westerly anomalies converging with northwest-to-westerly anomalies at the quasi-monthly scale with 23.2%variance contributions to the total rainfall variance,which are associated with an anticyclonic anomaly over the SCS and an eastward-propagating cyclonic anomaly over North China,respectively.At the synoptic scale,it occurs in south-to-southwesterly anomalies converging with a cyclonic anomaly on the downstream of the Yungui Plateau with 49.3%variance contributions.In both cases,the lower-tropospheric mean south-to-southwesterly flows provide ample moisture supply and potentially unstable conditions;it is the above synoptic,quasi-biweekly or quasimonthly disturbances that determine the general period and distribution of persistent heavy rainfall over South China. 相似文献
2.
Impact of precipitating ice on the simulation of a heavy rainfall event with advanced research WRF using two bulk microphysical schemes 总被引：1，自引：0，他引：1
G. A. Efstathiou N. M. Zoumakis D. Melas P. Kassomenos 《Asia-Pacific Journal of Atmospheric Sciences》2012,48(4):357-368
In this study, the Weather Research and Forecasting (WRF) model version 3.2 is used to examine the impact of precipitating ice and especially snow-graupel partitioning in the simulation of a heavy rainfall event over Chalkidiki peninsula in Northern Greece. This major precipitation event, associated with a case of cyclogenesis over the Aegean Sea, occurred on the 8th of October 2006 causing severe flooding and damage. Two widely used microphysical parameterizations, the Purdue Lin (PLIN) and WRF Single-Moment 6-class scheme (WSM6) are compared with available raingauge measurements over the complex topography of Chalkidiki. To further investigate the importance of snow and graupel relative mass content and the treatment of precipitating ice sedimentation velocity, two older versions of the WSM6 scheme were compiled and run with the current model. The verification results indicate that all simulations were found to match raingauge data more closely over the eastern mountainous Chalkidiki peninsula where maximum accumulations were observed. In other stations all schemes overestimate 24h accumulated rainfall except a station situated at the western part of the peninsula, where none of the simulations was able to reproduce observed rainfall. Graupel dominance in PLIN generates rapid precipitation fallout at the point of maximum predicted 24h accumulation. Similar behavior is shown in WSM6 from WRF version 2, but with significant less rainfall. Increasing snow amounts aloft, due to the unified treatment of precipitating ice in WSM6 from WRF version 3, modifies rain dynamics which decrease rainfall rates, but increases 24h accumulations. A sensitivity experiment where PLIN is used with snow accretion by graupel turned off, indicated that this process seems to be the most important factor controlling the differences in surface precipitation between PLIN and WSM6 from WRF version 3, determining the spatial and temporal distribution of this heavy precipitation event. The results also revealed that snow overestimation can lead to high rainfall accumulations, even though rain is more evenly distributed over the 24h period, deteriorating precipitation forecast. 相似文献
3.
2008年6月广东省连续性暴雨的成因 总被引：7，自引：5，他引：2
利用NCEP/NCAR再分析资料,分析2008年6月12-18日广东省连续性暴雨过程的环流背景及成因。结果表明：在中纬短波槽和南支槽活跃的环流形势下,低层低涡切变线和西南急流引起的强烈上升运动是这次广东省连续性暴雨的触发因子。孟加拉湾和西北太平洋的2支水汽在南海汇合,持续向华南输送暖湿空气,并由经向风场辐合形成较强的水汽辐合中心。连续性暴雨期间,华南上空异常加热源有利于其西北侧低空异常气旋性环流的维持和广东省沿海地区西南急流的稳定存在。异常偏强的水汽输送辐合和大气热源加热是这次连续性暴雨得以维持的重要原因。 相似文献
4.
Christos H. Halios Costas G. Helmis Helena A. Flocas Stephan Nyeki Dimosthenis N. Assimakopoulos 《Meteorology and Atmospheric Physics》2012,118(3-4):107-115
Synoptic climatology relates the atmospheric circulation with the surface environment. The aim of this study is to examine the variability of the surface meteorological patterns, which are developing under different synoptic scale categories over a suburban area with complex topography. Multivariate Data Analysis techniques were performed to a data set with surface meteorological elements. Three principal components related to the thermodynamic status of the surface environment and the two components of the wind speed were found. The variability of the surface flows was related with atmospheric circulation categories by applying Correspondence Analysis. Similar surface thermodynamic fields develop under cyclonic categories, which are contrasted with the anti-cyclonic category. A strong, steady wind flow characterized by high shear values develops under the cyclonic Closed Low and the anticyclonic H–L categories, in contrast to the variable weak flow under the anticyclonic Open Anticyclone category. 相似文献
5.
利用1959～2013年台站逐日降水观测资料和JRA-55逐6小时再分析资料,分析了长江中下游地区夏季强降水对应的前期三维环流结构。通过对长江中下游地区373个强降水样本的大气环流场合成分析发现,在长江中下游地区对流层中上层存在暖异常,暖中心位于300 hPa。在静力平衡和准地转平衡的作用下,高层暖异常上层存在反气旋式环流,下层存在气旋式环流。一方面,暖异常通过高层的反气旋式环流异常,使得其北侧的200 hPa西风增强,并促使高层急流东伸、南移到长江中下游地区北侧附近,增强了长江中下游地区高空辐散;另一方面,暖异常通过低层的气旋式环流异常,加强了吹向长江中下游地区的西南风,使低层水汽输送及辐合增强。暖异常所引起的高低空环流异常的有利配置,对长江中下游地区夏季强降水形成有重要作用。300 hPa 暖异常在降水前48小时已经存在于青藏高原东部的400～300 hPa 高空,700 hPa 气旋式环流提前24小时出现在四川盆地中低层。高低层的环流要素相互配合并随时间东移,暖异常率先到达长江中下游地区,并配合低层气旋式环流和水汽辐合区,导致了长江中下游地区的强降水。 相似文献
6.
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
7.
20世纪90年代以来东北暴雨过程特征分析 总被引：7，自引：2，他引：5
使用1990～2005年全国730站日降水资料和NCEP格点分析资料对1990～2005年东北地区大暴雨过程进行了分类研究,探讨21世纪前后夏季东北暴雨的主要特征.按照东北地区日降雨量大于50 mm的站点数不少于5个的标准,统计出1990～2005年东北地区的69个暴雨个例(共90天).在统计的基础上,进一步对造成大范围暴雨过程的天气形势进行分类研究.考虑阻塞高压、热带、副热带系统和西风带之间的相互关系,将暴雨过程的主要影响系统大致分为6类:(1)台风与西风带系统(西风槽、东北低涡)的远距离相互作用(20个,28.9%);(2)登陆台风(或南来低涡)北上与西风带系统(西风槽、东北低涡)相互作用(16个,23.2%);(3)台风直接暴雨(1个,1.5%);(4)低槽冷锋暴雨(16个,23.2%);(5)低空切变型暴雨(2个,2.9%);(6)东北低涡暴雨(14个,20.3%).在所有个例中与台风有关的共有37个,超过一半,占总数53.6%.台风的远距离水汽输送或登陆台风北上与西风带系统相互作用是东北地区产生大暴雨或持续性大暴雨的重要环流条件.此外,东北低涡和西风槽前系统造成暴雨个例也比较多,也是东北地区大范围暴雨的重要影响系统,低槽冷锋暴雨和东北低涡暴雨也各分为4小类.低空切变暴雨的切变线一般在低层较为明显.上述分析表明,夏季东北地区暴雨过程种类繁多,情况较为复杂,且进入新世纪以来该区降雨过程较为活跃,值得深入研究. 相似文献
8.
Koji Nishiyama Shinichi Endo Kenji Jinno Cintia Bertacchi Uvo Jonas Olsson Ronny Berndtsson 《Atmospheric Research》2007,83(2-4):185-200
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.
春夏季青藏高原积雪对中国夏末秋初
降水的影响及其可能机制 总被引：5，自引：1，他引：4
本文首先利用最大协方差分析方法,探讨青藏高原积雪与中国降水之间的联系,发现中国夏末秋初（8～10月,简称ASO）降水与前期及同期高原积雪有着显著联系,当春夏季青藏高原西部多雪时,其后ASO中国长江及其以南地区多雨,而东部沿海的狭长区域少雨。进一步引入最大响应估计等方法,研究中国区域降水对高原积雪异常的响应及其可能的物理机制,结果表明,冬春季高原多雪异常可持续到夏季,并通过改变地表热力状况,导致ASO南亚高压减弱,同时在高、低空激发出两支波列:高层200 hPa波列沿中高纬西风急流传播,自高原经蒙古到达日本呈现明显的“负—正—负”位势高度异常传播,日本上空为气旋性异常环流;低层850 hPa波列起于高原,经孟加拉湾至中国南海,沿着西南气流传播,导致台湾附近的反气旋性异常环流,其西侧的偏南气流,将南海丰富的水汽输送至中国南部湖南、广西;而高层中心位于日本的气旋性异常环流西侧的偏北气流利于北方天气尺度扰动向南移动,它们为长江中下游及其以南地区多雨提供了有利条件。进一步计算定常波波数也表明,高层西风急流与低层西南季风气流作为波导,有利于高原上空的扰动沿着高、低空2支通道向东传播。由于东部沿海浙江、福建为正位势高度异常区,低层反气旋性异常环流则抑制了该区域的降水。 相似文献
10.
热带气旋影响下浙江省强降水过程延伸期预报研究 总被引：1，自引：1，他引：1
利用2000—2011年NCEP/NCAR水平风场逐日再分析资料以及浙江省逐日降水量资料,基于低频天气图工具,识别出3种与浙江省台风强降水过程相对应的典型低频大气环流型。通过合成分析,划分了与C型环流场和C+SN型环流场相适配的天气关键区。进而结合历史个例,研究了台风强降水期间关键区内低频系统的活动特征,初步建立了热带气旋影响下浙江省强降水过程预报模型,并提出依据模型开展延伸期过程预报的基本思路。对2012年的回报结果表明,模型表现出较好的性能,并针对强降水过程延伸期预报中需要解决的问题,提出了若干思考与建议。 相似文献
11.
This study explores the time-lagged impact of the spring sensible heat (SH) source over the Tibetan Plateau (TP) on the summer rainfall anomaly in East China using the Weather Research and Forecasting model. Numerical experiments for 2003 indicate that a spring SH anomaly over the TP can maintain its impact until summer and lead to a strong atmospheric heat source, characterized both by the enhanced SH over the western TP and enhanced latent heat of condensation to the east. Wave activity diagnosis reveals that the enhanced TP heating forces a Rossby wave train over the downstream regions. A cyclonic response over the northeast TP brings about a low-level northerly anomaly over northern China, while an anticyclonic response over the western Pacific enhances the subtropical high and the low-level southerly on its western flank. As a result, cold and dry airflow from mid-high latitudes, and warm and wet airflow from tropical oceans converge around the Huaihe River basin. In addition, warm advection originating from the TP induces vigorous ascending motion over the convergence belt. Under these favorable circulation conditions the eastward-propagating vortexes initiated over the TP intensify the torrential rainfall processes over the Huaihe River basin. In contrast, additional experiments considering the year 2001 with weak spring SH over the TP and an overall southward retreat of the summer rainfall belt in East China further demonstrate the role of spring SH over the TP in regulating the interannual variability of EASM in terms of wave activity and synoptic disturbances. 相似文献
12.
2003年8月“巴蜀夜雨”过程的模拟和分析研究 总被引：6，自引：0，他引：6
结合中尺度数值预报模式AREM的数值试验和观测资料分析,对2003年8月川西地区的9次夜雨过程进行了模拟研究和综合分析.结果表明,在一定环流背景下,川西地区特殊地形引起的沿坡地的辐合上升运动和下垫面提供给低层大气的热通量所导致的大气层结不稳定,对川西夜雨的形成和发展有重要影响.白天,随着陆-气通量交换的增加,低层大气的温度和湿度逐步升高,并在午后达到极值.与此同时,低层偏南暖湿气流在盆地西部由于气旋性弯曲而形成的东北风在午后逐渐加强,这支气流在盆地西部被地形阻挡,产生爬升运动.辐合上升将低层高温高湿的大气向上输送,使得大气不稳定层结的厚度以及强度都增加;日落以后,低层大气的相对湿度随着气温的降低而增大,容易饱和而形成凝结,同时大气中积累了相当可观的对流有效位能,低层辐合抬升等因素容易触发不稳定能量释放,造成对流性夜雨天气.强烈的对流辐合运动需要周围大气的入流补偿,促使偏东风气流增强且向高空伸展,这令辐合抬升作用进一步增强. 相似文献
13.
Detailed spatiotemporal structures for the submonthly-scale (7–25 days) intraseasonal oscillation (ISO) in summer monsoon rainfall and atmospheric circulation were investigated in South Asia using high-quality rainfall and reanalysis datasets. The Meghalaya–Bangladesh–coast of the western Myanmar (MBWM) region is the predominant area of submonthly-scale ISO in the Asian monsoon regions. The distinct rainfall ISO is caused by a remarkable alternation of low-level zonal wind between westerly and easterly flows around the Gangetic Plain on the same timescales. In the active ISO phase of the MBWM, a strong low-level westerly/southwesterly flows around the plain and a center of cyclonic vorticity appears over Bangladesh. Hence, a local southerly flows toward the Meghalaya Plateau and there is strong southwesterly flow towards the coast along southeastern Bangladesh and western Myanmar, resulting in an increase in orographic rainfall. Rainfall also increases over the lowland area of the MBWM due to the low-level convergence in the boundary layer under the strong cyclonic circulation. The submonthly-scale low-level wind fluctuation around the MBWM is caused by a westward moving n = 1 equatorial Rossby (ER) wave. When the anticyclonic (cyclonic) anomaly related to the ER wave approaches the Bay of Bengal from the western Pacific, humid westerly/southwesterly (easterly/southeasterly) flows enhance around the Gangetic Plain on the northern fringe of the anticyclone (cyclone) and in turn promote (reduce) rainfall in the MBWM. Simultaneously, robust circulation signals are observed over the mid-latitudes. In the active phase, cyclonic anomalies appear over and around the TP, having barotropic vertical structure and also contributing to the enhancement of low-level westerly flow around the Gangetic Plain. In the upper troposphere, an anticyclonic anomaly is also observed upstream of the cyclonic anomaly over the TP, having wavetrain structure. The mid-latitude circulation around the TP likely helps to induce the distinct ISO there in conjunction with the equatorial waves. Thus, the distinct ISO in the MBWM is strongly enhanced locally (~500 km) by the terrain features, although the atmospheric circulation causing the ISO has a horizontal scale of ~6,000 km or more, extending across the whole Asian monsoon system from the tropics to mid-latitudes. 相似文献
14.
15.
本文分析了中国科学院大气物理研究所年代际气候预测系统IAP DecPreS的海洋同化试验（简称EnOI-IAU试验）在西北太平洋地区的海表面温度（SST）年循环的模拟技巧,并通过对比IAP DecPreS系统自由耦合历史气候模拟试验结果,在包含海气耦合过程的框架下讨论了耦合模式中西北太平洋夏季SST模拟差异,及其对亚洲季风区夏季季风降水模拟的影响。结果表明,EnOI-IAU试验较好地模拟出了西北太平洋各个季节的SST空间分布,并显著减小了原存在于历史气候模拟试验中持续全年的SST冷偏差。混合层热收支诊断分析表明,包含同化过程在内的海洋过程的模拟差异对西北太平洋海温的模拟提升有重要贡献。夏季,EnOI-IAU试验模拟的印度季风伴随的低层西风较观测偏东、偏强,且高估了赤道西太平洋区域的降水量值、低估了印度洋区域的降水量值。水汽收支分析显示,气旋式环流异常造成的水汽辐合异常是造成亚洲季风区降水模拟差异的主要原因。研究表明,较之历史模拟试验,EnOI-IAU试验中夏季西北太平洋地区SST增暖造成局地对流增强,进而使得局地产生异常上升运动,水汽辐合增强,造成西北太平洋地区降水模拟偏多,激发出低层西风异常及赤道外气旋式环流异常。该低层西风异常导致了北印度洋地区低层辐散异常,减小了原存在于历史试验中印度洋地区的正降水偏差。西北太平洋气旋式环流异常一方面增强了印度夏季风伴随的低层西风,使得更多的水汽从阿拉伯海输送到西太平洋暖池区域,增强了该区域的降水量;另一方面,该气旋式环流异常减小了历史模拟试验中中国南部区域偏强的低层风速,进而提升了模式对东亚低层西南风的模拟能力。 相似文献
16.
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
17.
Dongliang Yuan 《Theoretical and Applied Climatology》2009,96(1-2):3-15
This study is motivated by an interest in obtaining a new automated classification scheme of daily circulation types suitable for use throughout Europe. The classification scheme is performed on 500 hPa geopotential height anomalies (NCEP Reanalysis data, 2.5°×2.5°). Nine grid points represent the study area. Five anticyclonic types (Anw, Ane, A, Asw and Ase) and seven cyclonic types (C, Cnnw, Cwnw, Cwsw, Cssw, Cse, Cne) are defined. Each of the circulation types has a distinct underlying synoptic pattern that produces the expected type and direction of flow over the study area. The classification scheme is applied to three different case studies in the Mediterranean Basin: Greece, Cyprus and central Italy. The precipitation percentage of the cyclonic type and the mean seasonal correlation coefficients for all circulation types are the two criteria used to evaluate the performance of the classification scheme. The ability of the HadAM3P general circulation model to reproduce the mean pattern and frequency of circulation types at the 500 hPa level in comparison to the NCEP dataset for the period 1960–1990 is also evaluated. The percentage of rainfall that corresponds to the cyclonic circulation types is greater than 85% for the three study regions. Furthermore, the correlation coefficients for the three classifications are very encouraging, for nearly all days of the study period. Compared to observations, the GCM is able to capture the mean patterns but not able to replicate exactly the observed variability of the circulation types over the three study regions. 相似文献
18.
利用1998年6～8月松嫩流域95个测站的逐日降水和NCEP/NCAR逐日再分析资料，通过诊断分析方法，对1998年松嫩流域东北冷涡大暴雨的形成过程及其大气环流背景，暴雨过程的降水性质与水汽输送特征，大气低频振荡与持续性降水的关系，以及东北冷涡暴雨随季节变化的特征等问题进行了探讨。结果表明，1998年松嫩流域较长的冷涡雨季中所发生的多次东北冷涡暴雨过程是很有代表性的，它们是大气环流由春末夏初到盛夏过渡不同进程中的产物，因而具有不同的环流背景和降水性质，且在洪涝灾害的形成中起着不同的作用，特别是亚洲季风水汽输送以及东亚大气30～50d和10～20d低频振荡对降水的持续性和阶段性变化均有至关重要的影响。 相似文献
19.
Arti B. Bandgar J. S. Chowdary C. Gnanaseelan 《Theoretical and Applied Climatology》2014,118(1-2):69-79
The Northwest Pacific (NWP) circulation (subtropical high) is an important component of the East Asian summer monsoon system. During summer (June–August), anomalous lower tropospheric anticyclonic (cyclonic) circulation appears over NWP in some years, which is an indicative of stronger (weaker) than normal subtropical high. The anomalous NWP cyclonic (anticyclonic) circulation years are associated with negative (positive) precipitation anomalies over most of Indian summer monsoon rainfall (ISMR) region. This indicates concurrent relationship between NWP circulation and convection over the ISMR region. Dry wind advection from subtropical land regions and moisture divergence over the southern peninsular India during the NWP cyclonic circulation years are mainly responsible for the negative rainfall anomalies over the ISMR region. In contrast, during anticyclonic years, warm north Indian Ocean and moisture divergence over the head Bay of Bengal-Gangetic Plain region support moisture instability and convergence in the southern flank of ridge region, which favors positive rainfall over most of the ISMR region. The interaction between NWP circulation (anticyclonic or cyclonic) and ISMR and their predictability during these anomalous years are examined in the present study. Seven coupled ocean–atmosphere general circulation models from the Asia-Pacific Economic Cooperation Climate Center and their multimodel ensemble mean skills in predicting the seasonal rainfall and circulation anomalies over the ISMR region and NWP for the period 1982–2004 are assessed. Analysis reveals that three (two) out of seven models are unable to predict negative (positive) precipitation anomalies over the Indian subcontinent during the NWP cyclonic (anticyclonic) circulation years at 1-month lead (model is initialized on 1 May). The limited westward extension of the NWP circulation and misrepresentation of SST anomalies over the north Indian Ocean are found to be the main reasons for the poor skill (of some models) in rainfall prediction over the Indian subcontinent. This study demonstrates the importance of the NWP circulation variability in predicting summer monsoon precipitation over South Asia. Considering the predictability of the NWP circulation, the current study provides an insight into the predictability of ISMR. Long lead prediction of the ISMR associated with anomalous NWP circulation is also discussed. 相似文献
20.
The present study investigates the interannual variation of June–November synoptic disturbance activity over the western North Pacific(WNP) and its relationship with large-scale circulation for the period 1958–2014. Two leading modes of eddy kinetic energy for the disturbance variability over the WNP are obtained by EOF analysis, characterized by anomalous eddy kinetic energy over the subtropical WNP and around the Philippines, respectively. These modes explain a large portion of the interannual variance of synoptic disturbance activity over the WNP. Both are associated with lower-level cyclonic anomalies, but with different locations: over the subtropical WNP for the first mode and over the South China Sea for the second mode. Considering the impact of ENSO on synoptic disturbance activity over the WNP, we repeat the analyses after removing the effect of ENSO, which is simply defined as the components linearly regressed onto the Ni o3.4 index, and find similar results, suggesting that the leading modes and their relationships with large-scale circulation exist without SST effects.Further analyses suggest that the meridional shear of zonal winds caused by cyclonic anomalies is crucial for maintaining the leading modes through barotropic conversion. 相似文献