A Jinan Heavy Rainfall on 18 July 2007

Jinan is stricken suddenly by an extraordinary rainstorm on 18 July 2007. From 17:30 to 20:30, the maximum rainfall of the city exceeds 153.1 mm. An synthetic analysis of this heavy rain event is performed, using multiple data, including FY-2 double satellite data, NCEP 6-hour reanalysis data, routine observational data and automatic meteorological station data. The results show the heavy rainfall takes place under the favorable large-scale circumfluence, which includes the continental high pressure in west China developing eastward, and Jinan locates at the northeast of it. At the same time, coupling between a high level jet steam and a low level jet steam intensifies, and becomes strong divergence in the upper and strong convergence in the low over Jinan. The cold vortex in northeast China develops dramatically, and the cold air of its rear strengthens. The short wave trough at middle layer moves eastward, and lies over the shear-line in the low level. Both of them form the shape of forward trough. All of these lead together to atmospheric stratification around Jinan turning very unstable. This rainfall process is caused directly by strong meso-scale convective cloud, which is formed by the mergence of two deeply convective clusters at the tail of frontal clouds, and it shows a quasi-round shape structure of a horizontal scale of 200 km×200 km, and a time scale of no more than 5 hours. There is a meso-scale low pressure over the surface corresponding to the cloud. The heavy rain occurs during the rapid intensification stage of the meso-seale convective system. In addition, the transport of warm and moist southwest air current in the low-level leads heavy rain to develop strongly. This water channel extends northeastward and shows northeast-southwest orientation via Jinan, which provides plenty of water for rainfall.