摘要:热带气旋远距离暴雨（TRP）往往成为高影响天气，是业务预报难点。本文用地面、探空观测资料、雷达遥感资料以及NCEP一日四次0.5°×0.5°再分析资料，对2018年第22号台风“山竹”登陆广东期间在长江三角洲（简称长三角）地区引起的远距离暴雨过程进行分析。结果表明：（1）这是一次发生在副热带高压（简称副高）控制范围内的热带气旋远距离暴雨，低层受台风倒槽影响。（2）这次过程第一阶段暴雨主要是在强的对流不稳定条件下，由对流层低层“山竹”倒槽中的辐合线触发对流产生，同时对流层高层“山竹”的极向流出汇入加大了中纬度西风风速，在长三角地区上空产生辐散，有利于上升运动的维持。第二阶段，对流不稳定条件有所减弱，但前一阶段强回波产生的低层偏北外出气流与东南风形成辐合线，辐合线上还有中γ尺度的涡旋产生，又促进了对流发展。850 hPa台风倒槽北端形成一个低涡，500 hPa副高边缘发展出一个短波槽，暴雨的动力条件更为有利。（3）长三角的3个强降水中心分别在长江口、杭州湾北岸的嘉兴沿海及宁波沿海，都是在水陆边界附近。（4）远距离暴雨区的涡度收支诊断发现：暴雨的初始扰动主要由近地层水平辐合辐散项提供，850 hPa的水平辐合辐散项和扭曲项共同作用形成和加强低涡，并通过垂直运动上传使中层700～500 hPa附近涡度增长，进而发展出500 hPa短波槽。850 hPa涡度来自于台风倒槽和副高边缘的偏南急流。（5）在这次远距离暴雨过程中，台风“山竹”与海上西太平洋副高之间形成偏南低空急流，向长三角输送水汽，这与典型TRP事件相似。不同之处在于：典型TRP中暴雨的初始扰动一般由西风槽提供，而这次过程主要由低空台风倒槽和偏南急流提供，涡度上传形成高空短波槽，是不同于典型TRP事件的一个物理过程。
关键词:台风“山竹”/
远距离暴雨/
副高/
短波槽/
涡度收支
Abstract:TRP (Tropical cyclone Remote Precipitation), usually a high-impact weather phenomenon, is difficult to forecast accurately. In this paper, ground and sounding observation data, radar remote sensing data, and NCEP re-analysis data at 0.5°×0.5° resolution and 6-h intervals were used to analyze the physical process of the long-distance rainstorm in the Yangtze River Delta region associated with typhoon Mangosteen during its landfall in Guangdong Province in 2018. The results show that: (1) The TRP event occurred under the control of the western North Pacific subtropical high, and was affected by typhoon’s inverted trough in the lower layer. (2) The heavy rain in the first stage was mainly caused by strong convective instability, which was triggered by a convergence line in the typhoon Mangosteen inverted trough in the lower troposphere. Mangosteen poloidal outflow at upper levels merged into the mid-latitude westerly wind over the Yangtze River Delta region, thus strengthening upper divergence and upward movement in the rainstorm area. In the second stage, convective instability was weakened, but a low pressure vortex had been formed at the north end of the typhoon’s inverted trough at 850 hPa and a short-wave trough developed subsequently at the edge of the subtropical high at 500 hPa, so that dynamic conditions for a rainstorm were more favorable. (3) The three heavy rainfall centers in the Yangtze River Delta region were located at the mouth of the Yangtze River, along the coast of Jiaxing on the north coast of Hangzhou Bay and along the coast of Ningbo, all of which were near the land-boundary. (4) The diagnosis of vorticity budgets on the remote rainstorm area suggest that the initial disturbance of the rainstorm was mainly forced by the horizontal convergence and divergence terms near the surface, and then a low pressure vortex at 850 hPa developed due to the horizontal convergence and divergences terms combined with the twisting term. These were related to the lower-level southerly jet between the inverted trough and the subtropical high. Finally, vorticity was increased upward to the mid-layers (700–500 hPa), attributed to vertical ascending motion, resulting in the development of a short-wave trough at 500 hPa at the edge of the subtropical high. (5) In the formation of the long-distance rainstorm, a lower layer southerly jet formed between typhoon Mangosteen and the western North Pacific subtropical high to transport water vapor to the Yangtze River Delta area, which was similar to a typical TRP event. The difference is that the initial disturbance in a typical TRP is generally provided by the westerly trough in mid-latitudes, while in this rainstorm, it was mainly provided by Mangosteen’s inverted trough and the low-level southerly jet. Vorticity was then transported upward, leading to the development of a short-wave trough.
Key words:Typhoon Mangosteen/
Long-distance rainstorm/
Western Pacific subtropical high/
Short-wave trough/
Vorticity budgets
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