一次华南双雨带暴雨中的位涡演变与雨带间的相互作用

利用实况资料和WRF中尺度数值模式对2008年6月12日18时—14日00时的华南双雨带暴雨过程进行了数值模拟与诊断分析。结果表明:随着锋面的南压,在锋面的西南方向(广西沿海)生成一低涡,该低涡作为位涡源在中高层表现稳定,分别为锋面雨带(北雨带)与暖区雨带(南雨带)提供正位涡。南雨带对北雨带的作用主要体现在中层(112~114°E附近),南雨带中有位涡的大值向北输送,其输送过程导致两条雨带在该处相连,而在115°E以东的南雨带则无明显的输送过程。同时,北部高空槽中也有大值位涡向北雨带输送,以维持北雨带。研究还发现,本次过程中暖区暴雨与锋面暴雨雨带的结构差异明显,锋面雨带的结构与传统雨带的结构比较一致;有利于暖区暴雨降水的形势主要表现在中高层。RIP轨迹模式的结果也表明,质点在运动过程中位涡的输送源是位于广西沿海的低涡,可见该位涡源对双雨带形成有重要的作用。

Potential vorticity evolution of a double rainbands storm in South China and interactions between the rainbands

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.