2009年夏季四川盆地两次暴雨过程对比分析

利用NCEP1 °×1 °每6 h一次的再分析资料、常规气象站降水资料及探空资料，对2009年6月26-29日（“6·26”）和7月30日-8月2日（“7·30”）发生在四川盆地的两次暴雨过程进行对比分析。结果表明：（1）“6·26”暴雨过程降水影响系统主要是盆地中部的低槽及低层西南低涡，“7·30”暴雨过程则为两高之间的切变线、辐合线及西南低涡。（2）水汽通量流函数的对比分析显示，两次过程中水汽输送通道不同，“6·26”过程水汽主要来自孟加拉湾；而“7·30”过程则是孟加拉湾的水汽经中南半岛到达南海，与南海偏南气流汇合加强，向盆地中东部输送形成，且水汽通量的势函数及辐散分量对未来6 h累积降水的落区及中心有很好的指示作用。（3）中高层干冷空气向边界层下滑进入暖湿高能区，在埃克曼非平衡流向埃克曼平衡流调整过程中，强迫边界层中空气产生较强的垂直上升运动，且垂直运动延伸至中高层，同时激发中层的次级环流，可能是两次暴雨过程发生发展的重要物理机制。

Comparative analysis of two heavy rain events in Sichuan Basin during summer 2009

Two heavy rain events in Sichuan Basin are compared based on NCEP reanalysis, weather station precipitation and sounding da-ta. The first event is from 26 to 29 June and the second from 30 July to 2 August 2009. The conclusions can be drawn as follows. （1）＂6.26＂case is mainly affected by the low trough in central basin and southwest vortex, but the＂7.30＂case is attributed to the shear line between two high-pressure systems, inverted trough and southwest vortex. （2） Results based on water vapor flux stream functions demonstrate that the two cases have different water vapor transport channels, the vapor contributed to the ＂6.26＂case is mainly from the Bay of Bengal, while during the“7.30”heavy rain case the water vapor from the Bay of Bengal passed the Indo-China peninsula and merged with water vapor in the south China Sea and then transported to Sichuan Basin. The water vapor flux potential function and divergent component are important predictors for future 6-hour accumulated precipitation area and center. （3） The dry cold air at high levels declined into boundary layers and entered high energy area. During the adjustment of the Ekman non-balance flow in the boundary layer, the dry cold air induced strong vertical ascending motion in boundary layer which extended to the high levels. Meanwhile, secondary circulation system at middle levels is triggered by the dry cold air as well. This could be the important physical mechanism leading to the two heavy rain events.