Simulation of the Dynamic and Thermodynamic Structure and Microphysical Evolution of a Squall Line in South China

A squall line that occurred in south China on 31 March 2014 was simulated with the Weather Research and Forecasting model. The microphysical processes had an important influence on the dynamic and thermodynamic structure of the squall line. The process of water vapor condensation (PCC+) provided heat for the ascending movement inside the squall line. The forward movement of the heating area of PCC+ was an important reason for the squall line’s tilting. The convergence of the outflow of the cold pool and the warm and wet air constantly triggered new convection cells in the front of the cold pool, which made the squall line propagate forwards. The cooling process of graupel melting into rain corresponded closely with the rear inflow jet. During the mature period of the squall line, the effect of cooling strengthened the rear inflow jet. This promoted low-layer inflow and a convective ascending motion, thus further promoting the development of the squall line system. During the decay period, the strong backflow center of the stratospheric region cut off the forward inflow of the middle and low layer towards the high layer, and cooperated with the cold pool to cut off the warm and wet air transport of the low layer, making the system decline gradually.