Comparative Analysis on Two Severe Convective Processes in Hunan Province in 2020

Abstract

 In this study, two severe convective weather processes in late March 2020 are compared and analyzed based on the surface observation data, Doppler weather radar data, satellite black body temperature data and the reanalysis data from the National Centers for Environmental Prediction. The results show that the two severe convective weather processes both can be divided into two stages, warm advection forcing stage and baroclinic frontogenesis stage. For the second process the warm advection forcing is not significant. In terms of dynamic conditions, in both processes there is low-level convergence, high-level divergence, middle-low-level southwesterly jet, and the intrusion of cold air. The upward motion in the second process is more intense than that in the first process. In both processes, the upward motion in the warm advection forcing stage is weaker than in the baroclinic frontogenesis stage. In the aspect of water vapor conditions, the divergence of water vapor flux at 850 hPa in the second process is larger than that in the first process. The water vapor convergence center rises to the level above 800 hPa and lasts for a long time. Through the comparative analysis in different stages, it is found that the water vapor convergence in the two processes in the baroclinic frontogenesis stage is stronger than that in the warm advection forcing stage. For the thermal conditions, the cold-dry air at high levels is superimposed over the warm-wet air at low levels, presenting a thermal unstable stratification. In the first process, the intensity and vertical extension of the low-level warm advection is larger than that in the second process.  In both processes, the unstable energy is accumulated obviously in the warm advection forcing stage, and is released to a certain extent before the baroclinic frontogenesis stage. In the first process, there are 3 supercells within 100 km from ChangDe radar. In both processes, there are hails from 1900 BJT (Beijing Time) to 2000 BJT in Guanzhuang Town. The radar echoes both present the typical characteristics of hail. In the first process, the maximum reflectivity factor is larger, the intensity and vertical extension of mesocyclone are larger, the increase of vertical integrated liquid is more significant, and the high-level divergence is more intensive. Thus, the diameter of hail in the first process is larger.