A Case Study of Stratiform Cloud Structure and Precipitation Mechanism Based on Observation and Simulation

A wide range of precipitation occurred in mid-eastern region of China from 20 April to 21 April 2010. The purpose is to analyze the microphysical mechanism of the precipitation through airplane observation and simulation by the Weather Research and Forecasting (WRF) model. The airplane observation revealed a stratified structure in the cloud at an early stage of precipitation, and fluctuation of the Cloud Droplet Probe (CDP) droplet concentration was high. In middle stage of precipitation, CDP droplets existed mainly below 4.27 km; the peak at the maximum level of 3.69 km exceeded 100 cm^-3. Large-scale clouds and rain droplets also existed below 4.27 km. At 4.27 km and 3.69 km, several types of particle patterns were observed to include flakes and irregular, needle, and dendritic patterns. At 3.69 km, pattern of acicular and dendritic particles appeared in the areas of the least and most CDP droplet concentration, respectively. At 4.27 km and 3.69 km, the main particles were snow with a small amount of ice. In the late stage of precipitation, the cloud dissipated from the top, which indicates that few irregular clouds and rain droplets with no apparent CDP droplets existed at 3.9 km; rainfall formed mainly below this level. Several ice and snow particles appeared in the cold layer at this level. The simulation of WRF showed that the rain droplets were mainly formed below 2.9 km at the layer of 0 ℃. At heights of 2.2 to 2.9 km, snow melting to rain was the main factor in shaping rain droplets. Below 2.0 km, the rain droplets were formed by accretion droplets of rain. Snow droplets were mainly precipitation particles. Snow formed mainly through sublimation in the ice layer and through sublimation and riming in the mixed layer. The intensity of updraft and the content of supercooled water may have influenced the growth level of snow.