2011年梅汛期影响江苏两次大暴雨过程对比分析

利用常规观测资料、NCEP再分析资料及加密自动站资料对2011年梅汛期江苏省6月17-18日和7月11-13日2次典型的大暴雨天气过程进行对比分析.结果表明:2种不同类型大暴雨的影响系统不同、动力热力机制不同:“617”过程为江淮切变线大暴雨,切变线南侧的强劲西南低空急流输送了充足的水汽和能量,低层强冷空气活动触发了强暴雨;“711”过程为热带低压倒槽大暴雨,中低层弱冷空气垂直叠加在倒槽东侧偏南低空急流携带的海上暖湿空气上,构成了产生暴雨并持续的不稳定条件.垂直螺旋度上负下正的配置及非地转垂直环流上升支为两次暴雨提供了良好的动力抬升机制.暴雨发生在能量锋区南侧、湿位涡正压项零等值线靠近负值区一侧.位势不稳定度由强变弱,能量开始释放,预示暴雨即将开始.

A comparative analysis of two severe torrential rain processes in Jiangsu province during Meiyu period of 2011

Based on normal observation data, NCEP reanalysis data, and the intensive observation data of automatic weather station, a comparative analysis on two severe torrential rain processes during Meiyu period in Jiangsu province on June 17-18 and July 11-13, 2011 is performed. The results show that "617" case is caused by Yangtze-Huaihe River shear line, beside which, strong southwest low level jet as well as low level strong cold air activities supply abundant water vapor and energy, which ensure the occurrence and development of the heavy rainstorm; while "711" case is resulted from tropical depression trough, with middle-low level weak cold air overlying warm-wet air transported by southeast low leve jet, the unstable condition for heavy rain occuring and maintaining is produced. The coupling of helicity with a negative(positive) value at upper(lower) levels and ageostrophic vertical upward column provide favorable dynamic lifting mechanism. The two rainstorms occur in the south side area of energy front and negative area near zero isoline of the vertical component of moist potential vorticity. The potential unstability changes from strong to weak and unstable energy begins to release, which all indicate the beginning of heavy rain.