【作者】 甘晶晶；

【导师】 高坤；

【作者基本信息】 浙江大学 ， 气象学， 2010， 博士

【摘要】 江淮流域持续性暴雨过程是造成大范围洪涝的高影响天气事件,了解导致此类事件的全球和区域影响,对改进其预报是十分必要的。本文采用1951-2004年共54年全国日降水观测和NCEP／NCAR再分析资料,首先利用天气统计分析方法,揭示其天气气候特征；然后采用相关与合成分析相结合的方法,普查过程发生前30天内的中期信号,揭示其时空分布特征和天气学含义,并通过信号间链接关系的研究,初步构建江淮流域持续性暴雨过程中期形成机制的概念模型。江淮流域持续性暴雨过程存在三条中期信号链：“赤道太平洋信号链”源自过程前4-3周赤道东太平洋中高层暖高压异常,通过纬向遥相关向西传播,先后影响前3周澳大利亚附近中高层气旋性低槽发展和前2周中西亚地区气旋性低槽发展,最后影响前1周我国东南沿海副热带高压的加强西伸北抬；“南印度洋信号链”源自前4周南美洲东南侧极涡外缘深厚气旋性冷低压槽发展,它与澳大利亚低槽发展一起,通过能量频散促使前3周马达加斯加岛南侧气旋性低槽加强,该特征通过纬向风的经向遥相关引起中欧和中西亚分别出现反气旋性和气旋性风切变加强；上述两条信号链分别向中西亚传递的影响,激发“欧亚信号链”：前2周中西亚中高层气旋性低槽发展,能量快速向东频散,引起欧亚经向环流加强,我国东部沿海和白令海南侧低槽均随之发展,在过程前2-1周出现一次显著的欧亚波列发展过程。欧亚波列结束前后伴随出现明显的环流调整：中高纬白令海南侧低槽明显西退,促使鄂霍茨克海阻高的形成和稳定；在中纬度中西亚低槽逐渐东移并在巴尔克斯湖附近稳定下来,与减弱西退的东部沿海低槽趋于气旋性打通,形成宽平槽区,有利于弱冷空气频繁东移偏北南下；在副热带,随着我国东部沿海低槽减弱北抬,促使下游中低层西太平洋副高及其西缘的偏南风低空急流西伸加强,同时上游高层青藏高压及其东缘偏北大风东扩,二者在我国东南地区垂直重叠,导致经向垂直环流加强,其低空急流带来的暖湿空气与华北频繁南下的弱冷空气稳定交汇于江淮流域,形成持续性强雨带。显然上述欧亚波列结束前后伴随的环流调整的结果正是导致了有利于持续性暴雨产生的稳定环流特征的形成。本文最后选取1991年一次江淮持续性暴雨过程个例,根据过程前2-1周欧亚波列信号特征设计流场扰动进行初值集合模拟试验,结果表明：持续性强降水及其环流背景的模拟对于欧亚波列信号区的初始扰动是敏感的,该扰动对模拟环流的后继影响,确与持续性暴雨期间稳定环流特征的建立和维持有密切关系。更多还原

【Abstract】 Persistent heavy rainfall (PHR) events over the Yangtze-Huai river valley are one of the weather related high-impact events. To improve the forecast skill of the PHR events, it is necessary to find out the global-to-regional influences on the initiation and evolution of this kind of events. Based on daily rainfall data measured in China and NCEP/NCAR daily reanalysis for 54 years from 1951 to 2004, the climatology characteristics of the PHR events over the study area were firstly investigated, then the significant medium range signals from the global circulation prior to the PHR events were identified by the synoptical meteorology-correlation analysis, then the spatial-temporal distribution features and synoptic meanings of these signals were revealed, finally a tentative concept model of the medium range formation mechanism of the PHR events over the Yangtze-Huai river valley was constructed by synthetically analyzing the linkage between the signals.There are three chains of medium range signals for the PHR events. The first one, "Equatorial Pacific signals chain" originates from the development of upper level warm high over the eastern equatorial Pacific 4-3 weeks before the onset of the PHR events. By zonal teleconnection, it propagates its effects westerly thereafter to influence the developments of upper level cyclonic troughs near Australia and west Asia respectively 1-2 weeks later in succession, finally, to influence significant extending westward and jumping northward of the subtropical high near southeast China coast 1 week prior to the events. The second one, "South Indian Ocean signals chain" stems from the cold trough with cyclonic shear at periphery of polar vortex over southwest Atlantic 4 weeks before the onset of the PHR events. Then in company with the trough development at Australia, it causes the enhancing of the trough with cyclonic shear at south of Madagascar by energy dispersion mechanism. The signal feature of cyclonic shear near Madagascar then causes the anticyclonic shear in Central Europe and cyclonic shear in west Asia respectively by meridional teleconnection of zonal wind. The impacts of above two chains on the west Asia cyclonic trough trigger off the third signals chain, "Eurasian signals chain". The development of upper level cyclonic trough in west Asia disperses energy quickly downstream, which causes the development of two troughs at the East China coast and southern Bering Sea separately and induces significant Rossby wave-train activity over Eurasia during two weeks before the onset of the PHR events. With the disappearance of Eurasian Rossby wave train, significant adjustment of large scale circulation occurs. The west retreat of the trough at southern Bering Sea contributes to the occurrence and stability of Okhotsk blocking high. The trough in west Asia shifts eastward and simultaneously the trough in East China coast weakens and retreats westerly. Both of them connect to form a wider and flatter trough extending from Balkhash lake to northeast China, which favors propagating southeasterly of multi-minor-troughs with weak cold air in sequence. As the trough in east China coast shrink northward, the Subtropical West Pacific High (SWPH) extends westward along with low level southerly jet on the west frank of the SWPH and simultaneously the South Asia High (SAH) extends eastward along with upper level strong northerlies on the east frank of SAH. As a result, a local meridional circulation is developed in the southeast China with upper level northerly and lower level southerly. Obviously, it is above significant adjustment of circulation that results in the formation of stable circulation characteristics favoring the formation of the PHR events over the study area.As the last part of this thesis, an experiment of ensemble numerical simulation was conducted for a typical PHR event in 1991. To carry out the ensemble simulation, a series of initial wind disturbance which is based on the characteristics of Rossby wave train signals in Eurasian were imposed on the initial conditions of control experiment. The results indicate that the simulation of PHR event and corresponding circulation characteristics are sensitive to the Rossby wave train signals in Eurasian. The subsequent influences of the initial disturbances with the characteristics of that signals was closely relate to the establishment of the stable circulation during the PHR event.更多还原