冷空气斜压锋面系统对台风残留低压引发的暴雨影响机制研究

After making a landfall at the China coastal areas, a typhoon often encounters with continental cold air masses, which can usually result in the typhoon structure transformation from relative symmetry with warm core to baroclinicly asymmetric system through baroclinic forcing. Transformation of a typhoon has always been a hot topic in meteorological dynamic fields, with much attention being paid on the redevelopment of an extra-tropical cyclone transforming from a typhoon. However few studies have been carried out on the structure transformation of a typhoon inverse trough resulting in heavy rainfalls until nowadays..This project intends to do studies from three aspects on the transformation processes of a landfall typhoon at the coastal regions of Eastern China with means of dynamic analysis and numerical simulation, taking the cold front characteristics. The first study aspect will be focused on the interactions between cold air masses and landfall typhoons to help explore the cold front influence mechanism on heavy rainfall locations and intensities. The second study will be on the mechanism associated with the coastal area front genesis on the typhoon reverse trough transformation and torrential rainfall locations. The third aspect will be performed on the structures of cold air masses in favor of torrential rainstorm development, to explore how vertical environment wind shears interact with typhoon reverse troughs and further influences on rainstorm areas. The above studies will help provide scientific references to heavy rainfall forecasts.

我国沿海登陆台风经常能与大陆冷空气相遇，在冷空气的斜压强迫作用下，台风残留低压由相对对称的暖心系统变性为高度不对称的斜压系统。关于台风变性的研究已成为台风动力学领域的热点问题之一。目前的研究重点关注台风变性后温带气旋再发展。而台风变性阶段中，对引发暴雨的低压倒槽结构演变的研究目前还很少。.本项目拟从动力学分析和数值模拟等方面，结合我国华东及其沿海地区秋季冷空气斜压锋面系统的特点，对发生在这一地区的登陆台风变性过程进行分析。研究冷空气通过与登陆台风残留低压之间的相互作用，进而影响台风暴雨落区与强度的机制；研究在我国东部沿海特定海陆分布条件下，冷空气作用的沿岸锋生对台风倒槽演变的影响，从而影响暴雨落区的机制。揭示什么样的冷空气结构更有利于台风倒槽引起的暴雨发展，环境风垂直切变如何与台风倒槽相互作用进而影响暴雨落区的。为提高我国东部沿海地区登陆台风暴雨的预报准确率提供科学依据。

项目主要围绕冷空气类型和结构对登陆台风暴雨落区与强度的影响机制开展研究。（1）通过对“菲特”（1323）台风影响浙沪地区暴雨过程和环流形式的分析，发现造成致灾暴雨的系统就是低层浅薄冷空气和海上东风气流在沿海地区形成的沿岸锋。在对流层低层，东北风的强风速带形成冷空气垫，与海上东南暖湿空气对峙辐合。通过计算锋生函数的散度项，发现7日20时至8日02时冷空气东移南下和海上“丹娜丝”台风的靠近时，出现锋生的二次增强。通过数值敏感性试验发现，暴雨强度对冷空气强度和中心位置并不敏感，对沿岸锋生位置和暖湿空气强度更为敏感。(2)通过台风“麦德姆”(1410)和“苏迪罗”(1513)的冷空气作用形式及对台风暴雨的影响进行对比分析。发现“麦德姆”强降水经向特征明显；“苏迪罗”强降水纬向性较强。冷空气质点运动轨迹显示，“麦德姆”的冷空气沿西北路径入侵，包含西北冷槽和东北冷槽的共同影响；“苏迪罗”冷空气沿偏东路径入侵，冷空气源为单一的东北地区冷槽系统，强度较弱。在垂直方向上，“麦德姆”低层冷空气入侵早于高层，“苏迪罗”则相反。受冷空气不同作用方式影响，“麦德姆”台风倒槽明显，对流层低层冷暖平流较强，锋生显著，正涡度和上升运动沿台风倒槽呈东北-西南向分布；“苏迪罗”对流层低层冷平流及地面锋生均较弱，在台风北侧，低层偏东风急流引起较强的正涡度和上升运动，同时中层冷空气入侵有利于位势不稳定的增强，导致强降水沿台风北侧的偏东风急流呈东西向分布。冷空气入侵的结构决定了倒槽形状和暴雨落区。（3）通过地形敏感性数值模拟试验，发现杭州湾和杭州湾沿岸的地形高度及陆面类型都会对台风强降水产生较明显的影响。