中国台风特大暴雨综述

利用NCEP FNL 1°×1°再分析、地面观测和广东雷达等资料，对2018年8月27日—9月1日广东季风低压持续性特大暴雨过程进行了综合分析，主要结论如下：（1）在南亚高压稳定少动、西太平洋副热带高压呈异常双脊形态、强盛的西南季风低空急流北抬的大尺度环流背景下，季风低压显著发生发展并缓慢偏西移，促使本次广东持续性特大暴雨过程的发生。（2）季风低压的生命史可划分为两个阶段：波动加强阶段与减弱消亡阶段。季风低压强度演变与暴雨落区范围大小的逐日分布是同步，但与日最大降水量逐日演变不完全同步。在低压由强转弱并加速远离阶段（8月30日），处于季风低压外围倒槽区的粤东地区却发生了破纪录的极端暴雨。（3）粤东极端暴雨发生在边界层动力辐合及水汽辐合最强、对流层中低层的层结最不稳定阶段，中层南海高压与季风低压的相互作用为暴雨增幅提供了有利条件。来自海洋的偏南暖湿气流北推与前期MCS冷池出流相互作用导致粤东沿海地面辐合线的形成，辐合线西段受莲花山脉地形阻挡和抬升作用长时间停滞维持，致使极端强降水回波的触发和维持。（4）雷达回波演变可划分为三个阶段：块状弱回波西移阶段、带状回波叠加强短雨带东北移阶段和回波减弱东南移阶段。强降水回波呈典型的低质心暖云对流降水结构。

Spatial and temporal characteristics of warm season convection over Pearl River Delta region,China, based on 3 years of operational radar data

Using the NCEP finally reanalysis data (1°×1°),intensive AWS (auto weather station) data,Doppler radar data in Guangdong,the formation mechanism of a persistent torrential rain event associated with monsoon depression occurred in Guangdong from 27 August to 1 September 2018 was analyzed. The main conclusions are as follows. (1) Factors such as the atmospheric circulation environment of a strong stable SAH,the anomalous two-ridge of the western Pacific subtropical high and the strengthening northward southwest monsoon low-level jet are the reason why the monsoon depression has been strengthened considerably and moved slowly to the west. (2) The life cycle of the monsoon depression can be divided into two phases,which include the volatility increasing phase and the weakening phase. The evolution of the intensity of the monsoon depression coincides with the area of the heavy rainfall,but not with the maximum daily rainfall. When the monsoon depression weakened and moved away on August 30,the record breaking extreme torrential rain occurred in the eastern Guangdong is covered by the trough of the monsoon depression. (3) The most intensive boundary-layer wind convergence,the strongest water vapor convergence and the most instable convection stratification all occurred at the stage when the extreme torrential rain happened. Additionally,a surface convergence line is originally formed between the warm moist air southerly flow from the ocean and a cold dome generated by previous convection. The stagnation of the western part of the convergence line is blocked and uplifted by the Lotus Mountain,triggering and maintaining the echo of extreme torrential rain. (4) The evolution of radar echo can be divided into three stages:stage of weak scatter echoes moving westward,stage of belt-shaped echoes associated with strong and short rainbands moving northeast and stage of weakening echoes moving southeast. The echo of heavy precipitation has a typical structure of convective precipitation in the warm cloud with low mass center.