2019年韶关“5·18”局地特大暴雨极端性成因分析

ANALYSIS OF THE CAUSE OF TORRENTIAL RAIN ON MAY 18, 2019 IN SHAOGUAN

关键词:  特大暴雨  爬坡抬升  风速辐合辐散区  中气旋  触发机制

Key words:  torrential rain  hill-climbing  wind speed convergence and divergence zone  mesocyclone  triggering mechanism

摘要:

2019年5月18日，广东省韶关市出现了局地特大暴雨，刷新了韶关有气象记录以来的雨量记录。利用常规观测资料、区域气象自动站观测资料、韶关双偏振多普勒天气雷达资料，以及NCEP 1 °×1 °再分析资料对本次过程进行详细分析，探讨本次过程发生的极端性成因。(1) 本次过程是粤北历史罕见的局地暖区突发性特大暴雨过程，天气尺度的背景场较弱，极端性条件不显著，但能从中尺度分析场分析出暴雨潜势。(2) 暴雨发生之前，韶关一直处于偏南暖湿气流控制的区域，并且随着对流抑制减小为0，对流有效位能增强，自由对流高度下降至近地面，使得气块更容易被强迫抬升。(3) 多个单体持续发展与合并，出现“列车效应”，近地面冷池维持向南楔入，低层西南风加强叠加于冷池上导致强风速辐合辐散区和中气旋的出现，是维持强回波持续发展的重要原因；回波呈暖区降水的垂直结构特性，也呈现出近地面层冷池对暖湿气流强迫抬升的结构特征，侧面说明了强降水触发机制。(4) 地形对对流触发和暴雨的增幅有重要影响，峡谷和喇叭口地形加强了偏南气流的汇入及辐合作用，山前迎风坡除了地形抬升作用外，位于山前的地面辐合线对于对流既有触发又有加强与维持的作用。(5) 山前强水平温度梯度为对流发生提供了有利的环境条件，当初生对流出现降雨之后，水平温度梯度进一步加强，形成了温度梯度与对流强度之间的正反馈过程，因而对流持续发展与维持。(6) 对于此类突发的短历时强降水造成的暖区暴雨，监测和短临预警仍然是主要手段。

Abstract:

On May 18, 2019, there was a severe local rainstorm in Shaoguan, setting a new rainfall record since Shaoguan had meteorological records. In the present study, a detailed analysis of the process is carried out by using conventional observational data, regional meteorological automatic station observational data, Shaoguan dual-polarization doppler weather radar data, and NCEP 1 °×1 ° reanalysis data, so as to explore the reason why this rainstorm is so extreme and its predictability. The results are as follows. (1) This is a severe warm-sector torrential rain, which is rarely seen in northern Guangdong Province. The background field of weather scale is weak, and the extreme conditions are not significant. However, the potential of the rainstorm can be analyzed from the mesoscale analysis field. (2) Before the rainstorm, Shaoguan was in the area controlled by the warm and humid airflow from the south. With the decrease of the convective inhibition to 0, the convective effective potential energy is enhanced, and the free convective height drops to near the ground. (3) The strong superposition of the low-level southwesterly wind on the cold pool leads to the appearance of strong wind speed convergence and divergence zones and medium cyclones, which is an important reason for maintaining the continuous development of strong echoes. The echo shows the vertical structure characteristics of warm-sector precipitation, and presents the structural characteristic of cold pool in the near ground layer that forces the warm and wet airflow upward, which explains the triggering mechanism of heavy precipitation. (4) The terrain has an important influence on the triggering of convection and the increase of heavy rain. The canyon and trumpet-shaped topography strengthens the convergence of southerly airflow. Besides the topographic uplift, the convergence line on the ground in front of the mountain not only triggers but also maintains and strengthens the convection. (5) The strong horizontal temperature gradient in front of the mountain provides favorable environmental conditions for the occurrence of convection. After the initial rainfall of the convection, the horizontal temperature gradient is further strengthened, forming a positive feedback process between the temperature gradient and the convective intensity, so that the convection continues to develop and maintain. (6) Monitoring and short-term early warning are still the main means for such sudden short-duration warm-sector torrential rains.