| Based on observation analysis of a precipitating stratiform cloud system during March 20～21, 2005 in Henan Province, the macro- and microscopic features of the precipitating clouds, the water substance inflow and outflow structure and its microphysics conversion were studied with the ARPS model. The precipitation formation mechanism was also investigated.The study focused on a cold-frontal precipitation event caused by an upper southwesterly trough with a whole layer filled with warm water vapor from Bengali Bay. When it encountered the cold front from the north in the Central China, wet warm air was lifted slowly along the frontal surface, and large-scale systemic stratiform clouds were formed.The atmospheric hydrometeor and the surface precipitation decreased from the southern part to the northern part of Henan. The simulated cloud top was relatively flat with its mean height about 10 km. The mean simulated cloud base height was about 1 km, and the mean simulated height of 0℃level was about 3 km. The height of cloud top and 0℃level decreased from the south to the north of Henan, while the cloud base was lower in the southern Henan. The clouds had a distinct vertically-layered structure with ice cloud above 7 km, mixture cloud between 3～7 km, cloudless sections existed herein discontinuously, and liquid cloud between 1～3 km.During the precipitation, the inflow of vapor in the Henan region was mostly horizontal with weak contribution from surface evaporation. The model simulation indicated that horizontal vapor inflow was closely associated with the synoptic system and wind field. Horizontal vapor inflow was stronger than outflow when Henan located in the wet warm southwesterly flow ahead of the trough, vapor converged in the region. Horizontal vapor inflow became weaker than outflow when it located behind of the trough, and vapor appeared divergent, reducing precipitation. The main vapor inflow existed in the southern and western sides of Henan with strong inflow below 3 km. The eastern and northern sides were main vapor outflow with strong outflow below 1.5 km and between 2~5 km. The horizontal flow of hydrometeor was weaker compared with the vapor flow.The model simulation showed that there was some difference in the precipitation formation mechanism between the southern Henan and the north. Ice-phase water was approximately equivalent between the north and the south, but more liquid water and correspondingly more supercooled liquid water in the south. In the north, snow and graupel accreted via primary deposition and secondary collision-coalescence of supercooled liquid water, rain water was formed mainly via melting of snow and graupel, the dominate precipitation followed the"seeder-feeder"mechanism. With strong vaper condensation in the south, snow and graupel accreted via primary collision-coalescence of supercooled liquid water and secondary deposition, rain water was formed via both collecting cloud water existed abundantly in the low-layer and melting of snow and graupel, and the precipitation formation was a mixing of warm cloud process and"seeder-feeder"mechanism.The simulated distributions of precipitation efficiency, condensational and depositional precipitation efficiency were similar to observation with higher values in the southern Henan and lower in the north. The precipitation efficiency was lower than 20% in the northern Henan and higher than 20% in the south. It was higher than 50% in Xinyang district. The precipitation efficiency of deposition was higher than condensation in the north while it was lower in the south, which suggested the importance of cold cloud process in the north and together with warm cloud process in the south.
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