Numerical simulation and diagnostic analysis of rainstorm over Guangdong and Guangxi region on 19-20 May 2015

The 1°×1° NCEP/NCAR reanalysis data with temporal resolution of 6 hr and WRF 3.6 model were employed to simulate a heavy rain event in the region of Guangdong and Guangxi during the May 19-20, 2015. The simulation results were used to diagnosis its causes. Analysis results show that the torrential rain event is mainly affected by the interaction among the system of two troughs and one ridge, the subtropical high on 500 hPa, and the shear line and low vortex persistently existed at 850 hPa. WRF3.6 model can well simulate the rainfall intensity and the rainband distribution. Diagnostic analysis with simulation result shows that the convergence between the warm moist air flows on the edge of the subtropical high and the dry and cold airflow from large-scale westerly trough have provided the moisture condition for this heavy rain event. The vapor channel that was established by the low-level shear line persistently existed in the region of Guangdong and Guangxi and strong jet on 850 hPa have also provided for the moisture conditions and dynamic conditions. The upward movement in the heavy rain event is strong and deep, which contributed the transportation of warm moist air upward and the occurrence and development of heavy rain. The configuration of positive center in the low level and the negative center in the high level of spiral degrees, and the distribution of wet vortex with ξ_mpv1 < 0 and ξ_mpv2 > 0 also showed that the atmosphere is in an unstable state and was conducive to the development of convection.