引发渤海风暴潮一次江淮气旋北上过程诊断分析

Diagnostic analysis of a northward cyclone over the Yangtze-Huaihe Rivers causing storm surge in the Bohai Sea

利用NCEP再分析资料、常规气象观测资料和自动气象站观测资料对2013年5月26—28日西南地区一次江淮气旋北上入海减弱的过程进行了动力及热力分析。结果表明:副热带高压西北侧较强暖平流与青藏高压东北部冷空气促使江淮气旋发展北上,气旋入海后受下游日本海高压阻挡移动缓慢,高空槽与气旋由后倾结构变为前倾结构,槽后负涡度平流和负温度平流是气旋入海后减弱的主要原因。由于气旋移动缓慢,长时间向岸风配合天文高潮位引发了渤海风暴潮。对流层中低层的正温度平流和正涡度平流为江淮气旋的发展提供了动力及热力条件,湿位涡可较好的体现江淮气旋在发展过程中绝对涡度和大气稳定度的作用。非绝热加热作用出现在江淮气旋发展和消亡的整个过程,主要发生在气旋的偏东象限,其对气旋的发展和维持具有一定的贡献。高空急流辐合和引导气流减弱是江淮气旋入海后减弱并缓慢移动的另一个原因。

Using NCEP（ National Centers for Environmental Prediction） reanalysis data,conventional meteorological data and observational data from automatic weather stations,dynamic and thermal mechanisms of the weakening process of a cyclone over the Yangtze-Huaihe Rivers were analyzed when it moved northwards into the Bohai Sea during May 26-28,2013. The results show that intense warm advection at the northwest side of the subtropical high and cold air at the northeastern part of the Tibetan high make the cyclone moving northwards. Due to the blocking of the Japan Sea high, the cyclone moves slowly over the Bohai Sea,and the backwards-tilted structures of the high-level trough and the cyclone become forward-tilted. Negative vorticity and temperature advection behind the trough are the main reason for the declining of the cyclone. As the cyclone moves slowly over the Bohai Sea,a storm surge forms due to the long-time onshore winds and astronomical high tide. The advection of the positive temperature and vorticity in the middle and lower troposphere provide the dynamic and thermodynamic conditions for the development of a cyclone. Moist potential vorticity can reflect well the effects of absolute vorticity and atmospheric stability on the cyclone development. The diabatic heating effect occurs during the entire intensification and dissipation processes of the cyclone and mainly concentrates on the east side of the cyclone,which favors the development and maintenance of the cyclone on a certain degree. The convergence of upper-level jets and the weakening of steering flow are another reason for the cyclone moving slowly and declining over the sea.