Research On The Characteristics Of Vertical Airflow Velocity And Terminal Falling Velocity Of Hydrometeor Particles In Convective Cloud Fiel

The evolution of deep convective system is accompanied by the formation,developing and dissipation of convective cells in the field.The updraft is the driving force of the vertical development of the convective cloud,and the terminal velocity determines the movement trend of the hydrometeors in the clouds relative to the updraft,both of which jointly determine the development of the convective system and the intensity of the precipitation process.In this study,the WRF model coupled with a spectral-bin microphysical microphysics(WRF-SBM)was used to simulate the deep convective systems.The simulation results were processed by a three-dimensional cloud tracking algorithm to identify the individual cloud cells and trace their evolution,and to explore the characteristics of vertical velocity and mean terminal velocity in deep convective clouds.The main conclusions are as follows:The deep convective system is composed of multiple cloud cells.The life time of 80%convective cloud cells is less than 10 minutes.The number proportion of split clouds is the largest in convective cloud field,while the mass proportion of merged clouds is the largest one.By tracing the lifecycle of cloud cells,the individual cells in the cloud field are divided into the reversible dissipative cloud,the irreversible dissipative cloud,and the precipitation clouds.At the mature stage,the reversible dissipating clouds have negative buoyancy at the top accompanied by the downdraft,while the irreversible dissipating clouds have negative buoyancy at the cloud base and the cloud body is dominated by updraft,while precipitation clouds have rainfall at the surface and accompanied by downdraft.In the field of convective system,only a few cloud cells can develop upward to form deep convective clouds,while the cloud top height of most cells is limited.Deep convective clouds are more likely to be generated under meteorological environment like sufficient water vapor,unstable flow,small resistance of atmosphere to lifting,and strong vertical wind shear.The mass-weighted mean terminal velocity(V_m)or the number-weighted mean terminal velocity(V_n)of the hydrometeors in the cloud are positively correlated with the volume mean diameter.Based on the simulation results of WRF-SBM,the parameterizations of mean terminal velocity of five types of hydrometeors such as cloud droplet,raindrop,ice crystal,snow,and graupel,were established respectively under clean and polluted conditions.The results of the above parameterizations were compared with the results from parameterization of mean terminal velocity when the spectral shape parameter was set to a fixed value.It was found that the V_mvalue of the former one was generally smaller than that of the latter one for all types of the hydrometeors,while the change of V_nwas opposite.Further,the new parameterization scheme was applied to the Morrison microphysics scheme in WRF model.It was found that the change of terminal velocity parameterization results in the change of the vertical structure of different hydrometeors.The results in this paper provide a reference for further optimization of the mean terminal velocity parameterization scheme in the bulk microphysics scheme.