The environmental conditions and mesoscale system of a heavy rainfall over the central Shaanxi Plain on 8-9 August 2007
The process of a brief heavy rainfall on 8-9 August 2007 over the Central Shaanxi Plain was analyzed using the T213 data and high space and time resolution data including automatic meteorological observing station data.The results indicate that the brief heavy rainfall occurred under favorable large-scale ciuculation backgrounds,including the break of high-pressured dam,which resulted from the development merge of Qingqhai-Tibet Plain pressure and the west Pacific Ocean subtropical high in the middle level at 500 hPa,right flank divergence field of westerly jet entrance region in the upper level at 250 hPa and the shear line's development in the low level at 700 hPa.The amount of water vapor in storm experienced changes of decrease,sudden increase and fast decrease,which owed to wind direction fast changes at the low level.The vapor accumulation from surrounding areas of the Center Shaanxi Plain,which was achieved through the easterly current,had provided sufficient vapor and potential instability for the occurrence of the heavy rainstorm.The vapor increased so fast that the rainstorm occurred suddenly,and the rapid decrease of vapor made the rainfall last shortly.The dynamic mechanism of rainstorm was the formation of intense "pavement pumping" effect,the secondary circu lation circle and the asymmetric structure between the strong vertical upward movement and the weak dowdward movement due to the development of the upper anticyclone vorticity.The automatic meteorological observing satation data and satellite image data showed that the heavy rainfall was caused by the occurrence and development of MαCS,which came from the mergence and development of MβCS.The convective cells merged,developed and enhanced individually to form the different precipitation centers at Qishan,Liquan and Gaoling.The development of the convective cells resulted from the surface mesoscale convergence system.The changes of strength of the precipitation had a good corresponding relationship with that of the surface mesoscale convergence system.The formation and development of the ground mesoscale convergence systems may be the trigger and development mechanism for the heavy rainfall.
heavy rainfallcondition of circumstancehigh-pressure dam in the middle latitude regionmeso-β-scale convective system
国家科技期刊平台
NSTL
万方数据
维普
