“菲特”台风暴雨成因分析

201323号台风“菲特”是建国以来登陆我国的最强秋季台风，给浙江省带来暴雨天气。利用NCEP再分析资料从天气形势、动力、热力等方面对此次暴雨的成因进行了分析，结果表明：1）此次强降水可以分为两个阶段：第一阶段主要由“菲特”本身的环流引起；第二阶段由“菲特”残留云系长时间维持及其与弱冷空气的相互作用引起，且弱冷空气对降水的增幅作用十分明显。2）第一阶段水汽主要由其本身的环流提供，由“菲特”南侧的偏南风低空急流和东侧的偏东风低空急流从南海和西太平洋输送水汽，第二阶段水汽主要由“丹娜丝”外围的偏东风急流从西太平洋输送水汽。3）弱冷空气的扩散使斜压性增强，并使斜压位能释放转化为动能，促使台风残留低压环流加剧，并在台风外围东偏南暖湿气流之间形成中尺度辐合带，为暴雨天气的产生提供了良好的动力条件。4）弱冷空气叠加在950 hPa以下较强的暖平流之上，加剧了上冷下暖的不稳定层结，同时也使低层辐合加强．为暴雨区中尺度对流云团的发展提供了动力抬升机制。

Rainstorm Cause Analysis of the ＂Fitow＂ Typhoon

Abstract： Typhoon Fitow（201323） is the strongest autumn landing typhoon in China since the foun- ding of new China and caused heavy rain in Zhejiang. The causes of heavy rain are researched from the weather situation, dynamic and thermodynamic, etc by using the reanalysis data of NCEP. The results are as follows. 1 ） The heavy rain is divided into two stages, the first is caused by Fitow＇ s circulation it- self, while the second is caused by Fitow＇ s residual cloud long maintained and interacted with weakly cold air which is obvious to increasing precipitation. 2） The transports of water vapor in the first stage are provided by southerly jets on the south side of Fitow and easterly jets on the east side from the South Chi- na Sea and the Western Pacific, and the second stage is provided by easterly jets at Danas periphery from the Western Pacific. 3） The diffusion of weakly cold air enhances baroclinicity and releases baroclinic potential energy into kinetic energy, which develops the typhoon low pressure circulation and formats me- soscale convergence line between the typhoon periphery of east south warm moist air flow, which provides good dynamic conditions for the heavy rain. 4） The weakly cold air superimposed on the following strong warm advection at 925 hPa exacerbates the cold warm unstable layer and enhances low level convergence at the same time, which provides dynamic lifting mechanism for the development of mesoscale convective cloud in heavy rain areas.