Comparative analysis of continuous two strong coldness processes in late spring in March 2011 in Yunnan

Based on conventional observation data and NCEP 6-hourly reanalysis data with resolution 1°×1°, comparative analysis of two strong coldness processes (called process Ⅰ and process Ⅱ for short respectively) in Yunnan in middle and late March of 2011 was made.The results indicate that the reasons for surface temperature decreasing are different in the two processes because of different influence systems, and the intensity and range of the rain and snow are obviously different because of different height and strength of the vertical ascending motion. The increasing of water vapor flux and the vapor convergence in the mid- and low-level are the essential conditions causing the wide-spread snowfall in Yunnan, but the rainfall requires lower intensity of water vapor flux and vapor convergence than snowfall. Intensity and range of both rainfall and snowfall in processⅠexceed ones in processⅡbecause of stretching height of vapor convergence in processⅠwas higher than that in processⅡ. The greater horizontal gradient of instable energy near energy front zone is, the more accumulative energy was,and the more drastic weathers occur after energy released. The potential instability in processⅡis stronger than that in processⅠbefore late spring cold happened and thunderstorm range in Yunnan in processⅡis wider than that in processⅠafter late spring cold occurred. The uplift effect of dew-point front in the low-level can trigger release of strong unstable energy in the middle level, and the distribution areas of isodro-
sotherm have a certainly indicative significance for locations of rainfall, snowfall and thunderstorm.