副热带高压内部台风远距离暴雨特征和机制个例分析

A Case Study on Characteristics and Mechanism of Long-Distance Rainstorm Caused by Typhoon inside Subtropical High

摘要:

为了提高对副高内部台风远距离暴雨特征和机制的认识，综合利用多源观测和ERA5再分析资料，对2018年台风“山竹”在副高内部引发的一次远距离暴雨过程进行分析。结果表明：①这次暴雨发生在500 hPa副高内部高温、高湿、高能的强对流不稳定环境中，暴雨区位于低层台风倒槽北端、偏南气流风速辐合区和高空急流入口区右侧。②低层暖湿平流提供了充足的水汽和能量，促使对流不稳定层结发展和维持；高层强辐散耦合低层辐合形成强烈上升运动，为暴雨提供有利动力条件。③中尺度对流系统有3个演变阶段：带状对流组织和建立、对流带北移南侧超级单体发展和移动、北部对流减弱南部对流带新建发展，造成了两个阶段的极端短时强降水(100 mm/h以上)。④低层华北高压先后与台风倒槽、海上高压结合，增强了低层辐合并维持了切变线(地面辐合线)，利于对流的发展和维持。台风倒槽是初始对流带的触发和组织者，雷暴冷池出流是超级单体发展移动的关键因素。⑤高空急流的辐散抽吸强迫中层辐合，正涡度和低槽发展，暴雨区垂直风切变增强，利于南部对流带发展。当低纬度有台风活动时，500 hPa副高内部低层有台风倒槽，台风倒槽北端的辐合区是远距离暴雨预报的着眼点。

Abstract:

In order to improve the understanding of the characteristics and mechanisms of typhoon remote rainstorms within the subtropical high, a remote rainstorm process triggered by Typhoon Mangosteen in 2018 is analysed using multi-source observation and ERA5 reanalysis data. The results show that: (1) The rainstorm occurred within a strong convective and unstable environment characterised by high temperature, high humidity, and high energy within the 500 hPa subtropical high. The rainstorm area was located at the north end of the typhoon trough at the lower level, within the southerly wind speed convergence area, and to the right side of the upper jet stream inlet area. (2) The lower-level warm and humid advection provided sufficient water vapour and energy, promoting the development and maintenance of convective unstable stratification. Strong upper-level divergence coupled with lower-level convergence induced a strong upward motion, which provided favourable dynamic conditions for the rainstorm. (3) The mesoscale convective system exhibited three evolution stages: the organisation and establishment of banded convection, the development and movement of supercells in the south, the weakening of convection in the north, and the development of new convection in the south, resulting in extreme short-term heavy precipitation (exceeding 100 mm/h) during two stages. (4) The low-level North China high combined with the typhoon trough and the offshore high successively enhanced the low-level convergence and maintained the shear line (surface convergence line), which was conducive to the development and maintenance of convection. The typhoon trough acted as the trigger and organiser of the initial convective zone, and the outflow of the thunderstorm cold pool played a pivotal role in the development and movement of supercells. (5) The divergence and suction force of the upper jet stream in the mid-level convergence, the development of positive vorticity and low trough, and the enhancement of vertical wind shear in the rainstorm area were conducive to the development of the southern convective zone. During typhoon activity at the low latitudes, there was a typhoon trough at the lower level of the 500 hPa subtropical high, and the convergence area at the northern end of the typhoon trough was the focus of long-range rainstorm forecasts.