一次西南低涡造成华南暴雨过程的FY-2卫星观测分析

2008年6月11-13日华南发生了一次西南涡暴雨天气过程,其中,广西区有6个台站11日20时至12日20时的降水打破6月雨量历史纪录,分别为东兰306mm、环江218 mm、灵川270mm、桂林251 mm、柳城177mm和田林163 mm.采用FY-2卫星云图资料、NCEP再分析资料、常规观测资料及地面降水资料,对这次强降水过程的暴雨云团及其影响系统和环境场作了分析研究.结果表明:(1)红外和水汽图像配合,可以反映西南低涡发展东移过程中低层辐合带云系、高空扰动云系和弱冷空气的不同作用,云图的演变过程可以刻画强降雨发生时低层辐合、高层辐散的气流结构.(2)本次广西特大暴雨过程可分为两个阶段,第一阶段主要是西南涡东南侧的暖区降水,对流云团分布范围较广,中尺度对流系统具有涡旋状云系结构；第二阶段有弱冷空气南下,在边界层辐合线的组织下,中尺度对流系统组织成线状云带,南移消失.过程中,无论是红外云顶亮温随时间的演变,或者是红外与水汽亮温差的时间演变均可以反映云团的演变过程,并与强降水有较好对应关系.在局地要素满足暴雨发生的必要条件下,监测多通道亮温的急剧下降,可作为重要指标提前2～3 h预警强降雨的发生.(3)西南低涡暴雨云团出现在西南涡东南和南侧的南风盛行区域,云团发展伴有低空急流加强,同时,云系发展与500 hPa正涡度平流的贡献有关.

Observation and Analysis of a Southwest Vortex Rainstorm in Southern China Using FY-2 Satellite Data

During 11-13 June 2008, one south vortex (SV) rainstorm occurred in South China, in which the 24 h precipitation from 6 stations in Guangxi broke the historical record of daily precipitation in June, and they are: Donglan (306 mm), Huanjiang (218 mm), Lingchuan (270 mm), Guilin (251 mm), Liucheng (177 mm) and Tianlin (163 mm). Based on the FY 2C Infrared (IR) cloud imagery, NCEP reanalysis data, the conventional observation data and surface precipitation data, this paper analyzes the rainstorm cloud cluster, the impact system and ambient fields of this severe rainfall process. The results show that: (1) the infrared and water vapor images can reflect the different effects of the cloud system in mid and low level convergence zone, the upper air disturbed cloud system and weak cold airs when the SV moves eastward. The evolution process of the images depicts the flow pattern of the low level convergence and high level divergence when the rainstorm occurs; (2) This SV rainstorm in Guangxi has two stages in its life cycle. In the 1st stage, the rainfall forms in the warm side of the SV and the convection cloud clusters spread widely with rotation structures; in the 2nd stage, when the weak cloud airs move down from the north, the mesoscale convective system (MCS) of the SV becomes band shaped and dissipates. During the process, both the temporal evolutions of the infrared brightness temperature (TBB) and the TBB difference between the infrared and water vapor images are well corresponding to the evolution of the severe precipitation. By monitoring the rapid drop of multi spectral TBB, the severe rainfall warning could be issued 2-3 h in advance; (3) the rainstorm cloud cluster appears in the areas in the southeast and the south side of the SV, where the southerly wind prevails. Meanwhile, the developing of the cloud cluster is accompanied by the intensification of low level jet and the contribution of the positive vorticity advection at500 hPa.