Observation and Numerical Simulation of Cloud Physical Processes Associated with Torrential Rain of the Meiyu Front
WANG Pengyun* and YANG JingChinese Academy of Meteorological Sciences, Beijing 100081
Cloud micro-physical structures in a precipitation system associated with the Meiyu front are observed using the balloon-borne Precipitation Particle Image Sensor at Baoshan observatory station, Shanghai during June and July 1999. The vertical distributions of various cloud particle size, number density, and mass density are retrieved from the observations. Analyses of observations show that ice-phase particles (ice crystals, graupel, snowflakes, and frozen drops) often exist in the cloud of torrential rain associated with the Meiyu front. Among the various particles, ice crystals and graupel are the most numerous, but graupel and snow have the highest mass density. Ice-phase particles coexist with liquid water droplets near the 0℃ level. The graupel is similarly distributed with height as the ice crystals. Raindrops below the 0℃ level are mainly from melted grauple, snowflakes and frozen drops. They may further grow larger by coalescence with smaller ones as they fall from the cloud base. Numerical simulations using the non-hydrostatic meso-scale model MM5 with the Reisner graupel explicit moisture scheme confirm the main observational results. Rain water at the lower level is mainly generated from the melting of snow and graupel falling from the upper level where snow and graupel are generated and grown from collection with cloud and rain water. Thus the mixed-phase cloud process, in which ice phase coexists and interacts with liquid phase (cloud and rain drops), plays the most important role in the formation and development of heavy convective rainfall in the Meiyu frontal system.