Comparison Analysis of Two Warm-Area Torrential Rain Systems in Early Summer in Guizhou

Two warm-area heavy rain processes in 25- 26 May 2008( 0805) and 28- 29 June 2010( 1006) in Guizhou are analyzed based on the conventional observational data and the NCEP 1°×1° reanalysis data.The similar and different features of the two processes in early summer in Guizhou are compard.The results indicate that there is no cold air but warm low pressure near the surface when the two torrential rains occur.The low-level jet at 850 hPa enhances obviously,and the heavy rain areas are found in the left-front of low-level jet.What's different is that synoptic systems in middle and high levels in the two rain cases are different.In the 0805 heavy rain process the middle level is affected by plateau trough,but in the 1006 heavy rain case the mid-level system is the shear vortex between two high pressures while the high level is affected by South Asia high ridge.In the 0805 heavy rain case,several meso-β scale convective cells grow up and are combined in to a mesoscale convective syestem(MCS).The convective clouds develop severely.Base reflectivity of vertical cross section of Guiyang Radar shows it has warm cloud layer and mixing liquid phase layer.In the 1006 heavy rain case,the single meso-β scale convective cells grow up very quickly,finally into MCS.The convection develops strongly with a deep warm cloud layer.Analyzing their trigger mechanism,it is found that the key points to warm-area heavy rain in Guizhou lie in the building and enhancement of the low-level jet as well as the enhanced frontogenesis of convergence line in the surface low pressure.