低空急流在副高西北侧连续性暴雨中的触发作用

Trigger Role of the Low-level Jet for the Continuous Rainstorm in the Northwest Side of Subtropical High

利用NCEP1°×1°再分析资料、常规高空及地面资料,对2008年9月22—26日四川盆地西北部连续性暴雨的形成机制进行探讨。结果表明:此次暴雨产生在副高异常强盛和强台风黑格比登陆西进的环流背景下,过程期间500hPa无低值系统影响,暴雨的主要触发系统是副高和台风外围持续强劲的东南风低空急流,持续的东南风低空急流为暴雨区输送了源源不断的水汽和不稳定能量,急流最大风速出口区辐合及地形抬升为暴雨形成提供了辐合上升的动力条件,过程期间暴雨区位于一个稳定正环流的上升支中。另外,冷空气在此次过程中也起到了重要的作用。

Using NCEP global 1°×1° final-analysis data and the conventional high-altitude and surface data,the formation mechanism of the continuous rainstorm in the northwest side of subtropical high is discussed. The results show that the heavy rain happened in the background of the exceptionally powerful subtropical high and the strong Typhoon ＂Hagupit＂ landing westward, and there is no low-value system impact on 500hPa during the course. The main trigger systems are the subtropical high and continued strong southeast wind of low-level jet out of the typhoon. Continuous southeast wind of low-level jet provides rainstorm area the continuous water vapor and instability energy. The largest rapid zonal convergence speed and terrain elevation for the formation of rainstorm provide a driving force for increasing convergence conditions. The heavy rain district is located in a stable branch of ascendant circulation. In addition, the cold air in the process played an important role.