一次梅雨期台风远距离暴雨的分析研究

用NCEP 1°×1°再分析资料、MICAPS系统地面站资料、TRMM卫星降水资料以及自动站雨量资料分析了2011年梅雨后期发生在江苏省南京市的一次暴雨过程。结果表明:此次暴雨发生在中高层高空深槽前部、低空切变线附近、低层低涡和地面低压的东北部,是西风带低值系统及其引导的低层低涡与西进北上的"马鞍"台风共同作用产生的。925 h Pa上中国东南沿海位于低层低涡东北部的东南偏东气流影响下,将来自于西太平洋的水汽源源不断向暴雨区输送,为暴雨的发生提供了良好的水汽条件。不仅如此,此东南偏东气流还使得华南和东南沿海地区暖平流明显。低层暖平流输送伴随的小幅增温和水汽输送导致的湿度层增厚,导致南京附近大气层结不稳定是暴雨发生的热力环境。随着"马鞍"台风的西进北上,其北侧副高中的干空气逐渐被卷至中国东南沿海附近,与大陆上的暖湿气流形成明显对比,形成了一条明显的能量锋。与此同时,在长江中游地区,残余的梅雨锋也表现为一条能量锋,两条能量锋在南京附近相接,造成明显的上升运动,从而触发了暴雨的发生。

Analysis on a rainstorm related to remote typhoon during Meiyu period

With NCEP 1°×1° reanalysis data, ground station data of MICAPS system, precipitation data from TRMM satellite and rainfall data from automatic weather stations, a rainstorm process during the late Meiyu period of 2011 in Nanjing city is analyzed. The results indicate that this heavy rainfall occurred not only in the front of a deep trough in the mid-upper troposphere, but near the low-level shear line, as well as in the northeast of the low vortex in low layer and surface depression, which was caused by the combined effect of the mid-latitude low system of westerly zone with its accompanied low vortex in low layer and "Maon" typhoon moving north westly. In the southeastern coastal areas of China, the southeast-to-easterly flow in the northeast of the low vortex at 925 hPa transported water vapor coming from the West Pacific to the heavy rainfall area continuously, which provided favorable moisture condition for the occurrence of the rainstorm. Furthermore, the southeast-to-easter flow made warm advection obvious in South China and the southeastern coastal areas. The instability over Nanjing was the thermal environment for the rainstorm occurrence, which was led by slight warming induced by the warm advection in the low troposphere and the thickening of humidity layer caused by the water vapor transportation. Along with the northwest movement of "Maon" typhoon, the dry air on the north side of the subtropical high was gradually advected to the southeast coastal areas of China. As a result, an obvious energy front developed between the dry air and the warm moist flow on the mainland. Meanwhile, the remnant Meiyu front in the middle reaches of the Yangtze river area also changed to an energy front. Two energy fronts intersected near Nanjing, then gave rise to the apparent ascending motion, all of which triggered the heavy rainfall in Nanjing area.