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.