“8·25”上海大暴雨与东海气旋的相关分析

Correlation Analysis of the 25 August 2008 Heavy Rainfall in Shanghai with the Cyclone in the East China Sea

利用常规资料、卫星遥感和美国国家环境预报中心(NCEP)再分析资料、T639全球谱模式资料,详细研究了2008年8月25日早晨引发长江口两岸强对流大暴雨的东海锋面气旋和中气旋。利用涡度、垂直速度、假相当位温等物理量分析了东海锋面气旋和中气旋的生成原因。结果表明:稳定的西北太平洋副热带高压,使江南对流层下部气旋式切变长时间维持,当0812号热带气旋"鹦鹉"残体的部分动能、热能被输送到长江下游时,对流层下部暖低压因增热、降压而加深;当对流层中部西风槽正涡度、冷空气赶上并叠加到暖低压之上时,使暖低压发展成为锋面气旋。随着锋面气旋的发展和锋区的进一步加强,在暖锋上爆发强对流大暴雨和形成中气旋。

A mesoscale cyclone and a frontal cyclone in the East China Sea,which caused heavy rainfall in Shanghai on 25 August 2008,were analyzed from the conventional observations,satellite data,reanalysis data from NCEP(National Centers for Environmental Prediction),and spectral model data of T639.The generation of the two cyclones was analyzed by using vorticity,vertical velocity,and pseudo-equivalent potential temperature.The results showed that the cyclonic shear in the lower troposphere was kept for a long time because of the stability of the northwest Pacific subtropical high.The warm low in the lower troposphere developed due to warming by latent heat from the'0812'tropical cyclone,named as'Parrot'.When the positive vorticity and the cold air of westerly trough in the middle troposphere met with the warm low aloft,the latter developed to be a frontal cyclone.With development of the frontal cyclone and strengthening of the front,a mesoscale cyclone was formed to cause severe convection and produce heavy rainfall.