1617号鲇鱼台风登陆后引发不同性质暴雨的成因对比分析

Comparative analysis of causes of different types of heavy rainfall induced by typhoon Megi (1617) after landing

2016年9月28日1617号台风"鲇鱼"登陆后由台风本体环流和外围环流引发了不同性质的暴雨,这是本次秋季登陆台风暴雨预报的难点。利用常规气象观测资料以及NCEP的1°×1°再分析资料等,对不同性质暴雨的成因进行了诊断对比分析。结果表明:浙江东南部对流性降水和江西南部稳定性降水的大气层结结构具有明显的差异。中高纬度低槽距离台风较远,冷空气主要从低层入侵台风西北侧,破坏台风低层的暖心结构。台风外围中层干冷空气随东南风向浙江东南部输送,并叠加在低层暖湿气流之上,形成上冷下暖的不稳定层结,同时在对流层上层有干冷空气下沉至台风环流中下层(干侵入),导致浙江文成附近出现了局地特大暴雨。江西南部由于低层被湿冷空气占据,层结较为稳定,降水发展平缓。低空东南急流为台风外围环流暴雨提供了充足的水汽,浙江东南部地形对降水起到了增幅作用。不稳定层结及中层冷空气的输送对对流性暴雨的激发作用可以为登陆台风降水性质和强度预报提供参考依据。

The typhoon Megi (1617) was a large-scale and strong tropical cyclone. After typhoon Megi landed on 28 September 2016,different types of heavy rainfall were induced by body circulation and peripheral circulation of the typhoon,which was the difficulty of heavy rainfall forecasting for typhoon landing in autumn. Based on the convectional meteorological observation data and NCEP 1°×1° reanalysis data etc.,this paper diagnosed and compared the causes of different types of heavy rainfall in Zhejiang and Jiangxi provinces. Results show that there are obvious differences in atmospheric stratification structure between convective precipitation in southeastern Zhejiang and stable precipitation in southern Jiangxi. The trough in middle and high latitudes is far away from typhoon Megi. Cold air intrusion mainly occurs in the northwest side of typhoon from the lower level,destroying the low-level warm core structure of the typhoon. The dry and cold air at middle level around the typhoon is transported by southeast wind to southeastern Zhejiang. The dry and cold air is overlaid on the lower warm and wet airflow,forming an unstable stratification of upper cold and lower warm. Meanwhile,dry and cold air from the upper troposphere sinks into the middle and lower levels of typhoon circulation (dry intrusion),which results in local extreme heavy rainfall near Wencheng in Zhejiang. In southern Jiangxi,because the lower level is occupied by wet and cold air,the stratification is relatively stable and the precipitation develops slowly compared to that in Zhejiang. The low-level southeast jet stream provides abundant moisture for the heavy rainfall in the peripheral circulation of typhoon. The mountain topography in southeastern Zhejiang has played an increasing role in precipitation. The trigger effects of unstable stratification and transport of middle-level cold air on convectional heavy rainfall can be used as references for forecasting of precipitation characteristics and intensity of landing typhoon.