Observation And Numerical Simulation Of Physical Mechanism For A Typical Stratiform Precipitation

Microphysical structures of precipitation in JinLin Province on July 5th, 2004 impacted with the tropical cyclone are analyzed, based on PMS data, synoptic charts, satellite images, radar echoes and surface raindrop size distribution. Precipitation raindrop spectrum of this process are simulated by one dimensional raindrop category model and compared with observation.The tropical cyclone rainfall system mainly consists of altostratus, stratocumulus and fractonimbus according to observation. Vertical macro and microstructure of precipitation sheet clouds can be partitioned into five growth layers: (1)coring and depositing area near the cloud top; (2)active increasing of cloud drops and ice crystals between -7 and -2 degree centigrade; (3)aggregation of solid particles and evaporation of cloud drops from -2 to 0 degree centigrade; (4)a layer of melting and collision below 0 degree centigrade; (5)increasing areas of raindrops collision and cloud droplets condensation from 2500 to 1600 meters. Peak value of 2D-P mean diameter, maximum and peak diameter is corresponding with radar bright band echoes around the melting layer. Particle spectra observed by FSSP and 2D-P in different heights are fitted by means of Marshall-Palmer and multiΓformula, Khrgian-Mazin and multiΓformula respectively. Calculation shows that the fitting using multiΓis better. It is found that one density distribution function N(r)=mr~fexp(-ar+br~2-cr~3) can represent size distributions of small cloud drops, cloud drops and raindrops in the warm layer. The fitted spectrum distribution is well matched with the observed one. The calculated mean diameter, square-root diameter, concentration and liquid water content are also close to the observed results. Microphysical parameters and their fluctuations in different sites are revealed based on observations of raindrop spectra of stratiform-cloud precipitation. Numerical simulations show that raindrop category model performs well in describing raindrop spectrum of stratiform cloud in YiTong compared with Marshall-Palmer distribution in parameterization model.