The Meiyu front is a part of activities of the East Asiansummer monsoon. In this paper,the characteristics and detailed structures ofthe precipitation system in the Huaihe River Basinduring the Intensive Observation Period (IOP) of theGAME (GEWEX Asian Monsoon Experiment)/HUBEX(Huaihe River Basin Experiment) 1998 were investigatedwith dual Doppler radar, heat and moisture budgetanalysis, and numerical simulation to clarify the formation process of the precipitation systemsin the Meiyu front on the China Continent.
During the IOP, severe precipitation associated withthe Meiyu front was brought on 29 June and 2 July 1998.The precipitation event on 29 June was associated withthe Meiyu front moving northward in the subtropical air mass(ISA type), while the precipitation event on 2 July wasassociated with the Meiyu front which located on thepolar front (OPF type) and moved southward.
The ISA-type Meiyu front moved northward,and two types of precipitation systems formed in this front.One was the organized pair of the convective precipitationsystem on the convergence line near the ground, and thestratiform precipitation system formed to the north ofthe convective precipitation system. The other was thelinear convective precipitation system to the south ofthe convergence line near the ground.In the former precipitation area, the stratiformprecipitation system generated a cold pool nearthe ground. This cold pool intensified the localtemperature gradient to maintain the Meiyu front,although there were only weak or reversed thermal gradient in the subtropical air mass.In the latter precipitation area, because the airnear the ground was very moist, weak cold poolwas enough to cause the condensation to createa successive linear convective precipitation systemin the leading side.
The OPF-type Meiyu front had the temperature andmoisture gradient and moved southward, since thepolar air mass spread to 30 °N in latitude.This Meiyu front also accompanied with theorganized pair of the convective and stratiformprecipitation systems to the north of the convergenceline on the ground. However, there was not any precipitation system to the south of the convergence line,since the lifting condensation level (LCL)was higher than that in the ISA type; therefore,a new convective precipitation system was generatedwith the synoptic convergence. The difference of the precipitation processes betweentwo types of Meiyu fronts was caused by the differenceof the LCL to the south of the front, and the differenceof the LCL associated with the latitudinal front motion.