A STUDY OF TWO-BRANCH ONE-DIMENSIONAL NUMERICAL MODEL:EFFECTS OF CLOUD-PRECIPITATION DEVELOPMENT ON THE FORMATION OF VERTICAL CIRCULATION IN A SUPERCELL STORM

A one-dimensional time-dependent numerical model has been designed to simulate the vertical circulation in a supercell storm.The model includes two branches:one describes the developing process of cloud-precipitation and supplies the liquid hydrometeors;the other simulates the development of downdraft.The calculation indicates that the dry-cold ambient airflow breaking into the rearpart of cloud plays a critical role in the genesis of the downdraft in meso-scale circulations,while the transport of liquid hydrometeors satisfies the requirement for the persistance of moist adiabatic process,otherwise the downdraft will be damped.In addition,the simulation shows that the intensity of the downdarft varies with the strength of the ambient air injection,with the amount of liquid hydrometeor transport,and with the microstructure of hydrometeors.