四川盆地西北部9月两次低温暴雨过程对比分析

利用常规气象资料和NCEP 1°×1°再分析资料对2001年9月18日和2013年9月18日四川盆地西北部的两次暴雨天气过程进行对比分析。分析结果表明：两次暴雨均发生在无低涡且低温条件下,受西风槽东移的影响,最大降水发生在龙门山迎风坡,地形作用对两次暴雨形成有重要的影响;四川盆地内的水汽来源既可以来源于孟加拉湾,在有台风配合的情况下也可以来自于东海;2001年9月18日暴雨中低层低空急流为暴雨提供了有利的热力、水汽和动力辐合条件;2013年9月18日暴雨中地形造成的低层强烈辐合和南亚高压造成的高层强辐散为强降水提供了有利条件;对于低温条件下盆地西北部的暴雨需注意副高对西风槽的阻挡作用,同时需注意低层偏东风分量的大小。

Comparative Analysis of Two Heavy over Northwest Rain Processes with Low-temperature of Sichuan Basin

Using the routine observation data and NCEP 1°×1° final Operational Global Analysis data, two heavy rain processes occurring on 18th September, 2011 and 18th September, 2013 over Northwest of Sichuan Basin have been Analyzed and compared. Results reveal that the two processes are caused by westerly trough without vortex and high-temperature. Heavy rain areas are all located in the upward side of Longmenshan. The terrain has an important influence on heavy rain. The water vapor for Sichuan basin could come from the Bay of Bengal, it also could come from the East China Sea with the influence of ty- phoon. The low-level jet provided thermodynamic, moisture and the dynamic convergence for the heavy rain on 18th Septem- ber, 2011. The strong low-level convergence caused by terrain and the high-level divergence are the key factors for the heavy rain which happened on 18th September, 2013. The westerly trough blocked by subtropical high and east wind component of low-level should be noticed for the heavy rain with low-temperature over northwest of Sichuan basin.