长江中游地区极端降水主要天气系统类型分析

Weather system types of extreme precipitation in the middle reaches of the Yangtze river

利用2008—2015年5—9月湖北省60例极端降水过程常规观测和物理量资料及中尺度观测资料,主要应用天气诊断分析方法,研究了降水过程影响天气系统的演变机制、热力动力特征及强降水形成及维持原因,归纳出长江中游地区极端降水天气类型主要有锋面气旋、西南涡切变、西南涡-东北气旋、暖倒槽和登陆台风5类,其中前两类是最主要的极端降水类型。同时,指出不同天气类型控制下天气预报要关注的重点:(1)在锋面气旋类中,江淮气旋的发展是梅雨锋上重要的扰动系统,但梅雨期因冷空气势力弱江淮气旋并不强烈,分析时很容易忽视;(2)在西南涡切变类中,西南涡、新生涡和低空急流是梅雨锋切变线上重要的扰动系统,降水落区的差异与不同扰动系统的影响有关;(3)西南涡-东北气旋类降水落区一般位于两个系统结合部位,且极端降水绝大部分仅出现在梅雨锋西部;(4)暖倒槽类主要是局地极端降水,降水落区大多位于鄂西山地-江汉平原西部间过渡带。(5)登陆台风与副热带高压相互作用并形成稳定的有利形势,加上特殊地形作用,是强降水得到发展和维持的主要原因。

Based on the conventional observation data, physical data and mesoscale observation data of 60 cases of extreme precipitation in Hubei province from May to September during 2008-2015, the mechanism of weather system evolution, the thermal and dynamic characteris-tics of the systems, and the reason for formation and maintenance of heavy rainfall are studied by means of weather diagnosis. Five types for weather systems of extreme precipitation are summarized： the frontal cyclone type, the southwest vortex and shear type, the southwest vor-tex-northeast cyclone type, the warm low pressure inverse trough type and the landing typhoon low-pressure type. The first two are the most important types of extreme precipitation. At the same time, the key points of weather forecast under different weather types are pointed out： （1） For the frontal cyclone type, the development of the Jiang-huai cyclone is an important disturbance system in Meiyu front. But it is not strong because the cold air force is weak, so the Jiang-huai cyclone can be easily ignored in routine weather analysis during Meiyu period. （2）For the southwest vortex and shear type, the southwest vortex, the nascent vortex and the low-level jet are important disturbances in the Meiyu front, and the difference of the precipitation area is related to the influence of the different disturbance systems. （3） The precipitation area of the southwest vortex-northeast cyclone type is generally located at the junction of two systems, and most of the extreme precipitation occurs only in the western part of Meiyu front. （4）The warm low pressure inverse trough type mainly produces local extreme precipitation. And the precipita-tion mostly falls in the transition zone from the western Hubei mountains to the west of Jianghan plain. （5） Landing typhoon interacts with sub-tropical high and forms a stable favorable situation, coupled with special terrain, which is the main reason for the development and maintenance of extreme precipitation.