Abstract:The numerical simulation and diagnostic analysis of a double rainbands storm process from 1800 UTC 12 June 2008 to 0000 UTC 14 June 2008 in south China are conducted by using real time data and mesoscale numerical model WRF.The results show that:as the front moves towards south,a vortex is generated in Guangxi coastal area,which is located in the southwest of the front.As a source of potential vorticity,this vortex performs stably in the mid-high levels,providing positive potential vorticity for frontal rainband and warm sector rainband respectively.The main effects from southern to northern rainbands are mainly at middle levels,near 112-114°E.Large-value potential vorticity in southern rainband tranports towards north,leading to the connection of these two rainbands here,but in the east of 115°E,southern rainband has no obvious transport processes.At the same time,northern upper-level trough also transports large-value potential vorticity to the northern rain belt to maintain it.This study also finds that significant structure differences between warm area rainstorm and frontal rainstorm,and the structure is identified with frontal rainband and traditional rainband.The pattern in favor of warm area rainfall is mainly at mid-high levels,warm area rainband has the structure of three-layers with different properties.This structure is conducive to the maintenance and increase of the precipitation.RIP particle trajectory model also demonstrates that the potential vorticity transmission source in the particle movements is the vortex located in Guangxi coastal area,showing that this potential vorticity source plays an important role in the formation of these two rainbands.