NUMERICAL STUDY OF THUNDERSTORM ELECTRIFICA-TION WITH A THREE-DIMENSIONAL DYNAMICS AND ELECTRIFICATION COUPLED MODELⅠ:MODEL DESCRIPTION AND PARAMETERIZATION OF ELECTRICAL PROCESSES

Anew three-dimensional dynamics and electrification coupled model has been developed for investigating the characteristics of microphysics,dynamics and electrification inside thunderstorms.This model is basically modified from at hree-dimensional,time-dependent,and dual-parameter cloud model originally est ablished in IAP (Institute of Atmospheric Physics) and a two-dimensional axisym metric cloud dy namics and electrification coupled model.Primary modifications to the model include notonly the coupling of electrification with dynamical and microphysical processes,but also the lightning discharge process and screening layer effect at the cloud top as well.Apart from including a full treat ment of smallions with at tachment to seven classes of hy drom eteors(water vapor,clouddrops,rain,ice,snow,graupel and hail),the model considers ten microphysical processes which include condensation,deposition,evaporation,aut oconversion of cloud-rain,collection,freezing melting,nucle-ation,,and mult iplication of ice cryst als,and five electrif ication processes which include ionic diffusion,electric at traction,inductive charging,non-inductive charging and secondaryice crystal charging.The larger precipit ation particles are also forced by the vertical component of electrical force in electrical intensive thunderst orms.For the horizontal and vertical advection terms,fourth-order and second-order finite differences are used,and superrelax ation method is used to determine electric potential.