Numerical Simulation of Microphysical Process of a Cold Front Precipitation Cloud System in Autumn in Shijiazhuang Region

摘要

The mesoscale model WRF has been used to simulate the evolution of a cold front precipitaion cloud system on 4-5 October 2008 in Shijiazhuang region, China. Data from satellite, radar and routine observation were also utilized for comprehensive analysis. Results show that: both the middle-layer and upper-layer of the cloud system were cold-cloud structure while the lower-layer was warm-cloud structure, therefore, this configuration was beneficial to the occurrence of seeding-feeding precipitation mechanism. Hydrometeors in the cloud system were heterogeneous in space distribution, but vertical distributions of ice crystal, snow, graupel, cloud water and rain water had good agreements with the distribution of cloud system. The main microphysical mechanism of precipitation was that ice crystals became larger by accretion of supercooled water in fallen process and continued growing through the warm-layer. Both mechanisms of precipitation of cold-cloud and warm-cloud were verified to exist in the cloud system, and the start of precipitation depend largely on the former one. The fluctuation action in the relatively homogenous upflow field existed in the lower-layer of cloud system and formed owing to mesoscale convergence was the main cloud dynamic mechanism that convective clouds were embed in stratiform cloud and precipitation got enhanced.