弱天气背景下鲁南一次暖区大暴雨触发 与维持机制分析

利用区域自动站资料、ERA5再分析资料、FY-2F云顶亮温资料和多普勒雷达资料等，对2019年8月5—6日鲁南大暴雨过程的环流背景、环境场条件、中尺度对流系统（MCS）演变特征及其触发机制进行了分析。结果表明：（1）这次暴雨过程发生在副热带高压边缘的弱天气强迫背景下，大尺度环流形势配置不是很有利；（2）深厚的湿层、较低的抬升凝结高度（LCL）和自由对流高度（LFC）、上干下湿的不稳定层结为大暴雨的产生提供了有利的环境条件；（3）暖区强降水发生在鲁中山脉向苏北平原的过渡带上，呈狭长带状，5日午后和夜间先后生成的准静止β中尺度对流系统（MβCS）共同导致大暴雨过程的发生，小时强降水中心主要出现在MβCS云团TBB梯度大值区附近；（4）5日午后鲁南和6日凌晨枣庄中部强降水的触发机制为地面中尺度辐合线，MCS沿着辐合线不断新生和发展，形成“列车效应”，造成大暴雨。6日凌晨临沂西北部强降水由850 hPa露点锋触发，鲁中山脉峡谷风效应和迎风坡的动力抬升作用促使MCS增强发展；（5）强降水的持续与850 hPa露点锋、冷池和边界层暖湿气流增强引起的地面辐合线的长时间维持有关。

The Trigger and Maintenance Mechanism of a Warm-Sector Heavy Rainfall under Weak Synoptic Background in Southern Shandong

Based on regional automatic station data, ERA5?reanalysis data, cloud-top bright temperature of FY-2F and doppler weather radar data, etc., the circulation background, environmental field conditions, the mesoscale convective system (MCS) evolution characteristics and trigger mechanism of the heavy rainfall in southern Shandong Province during August 5-6, 2019, were analyzed. The results showed that: 1) This rainstorm process occurred under a weak weather background forcing at the edge of the subtropical high, and the large-scale circulation was not very favorable. 2) The deep wet layer, lower uplift condensation height (LCL) and free convection height (LFC), and the unstable stratification of upper dry and lower wet provided favorable environmental condition for the generation of heavy rain. 3) The warm sector heavy rainfall occurred in the transition zone from mountainous area of Mid-Shandong to the North Jiangsu Plain, in a narrow and long band. Quasi-steady MβCS generated successively in the afternoon and night of August 5 jointly led to the occurrence of heavy rainfall, and the hourly heavy precipitation centers mainly appeared near the TBB gradient maximum area of MβCS cloud cluster. 4) The trigger mechanism of heavy precipitation in southern Shandong in the afternoon of August 5 and in the middle of Zaozhuang in the morning of August 6 were the surface mesoscale convergence line, along which MCS was constantly emerging and developing, forming a "train effect" and causing heavy rainfall. The heavy precipitation in the northwest of Linyi was triggered by the 850 hPa dew point front in the early morning on the 6th, and the canyon wind effect and the dynamic uplift of the windward slope in mountainous area of Mid-Shandong promoted the development and enhancement of MCS. 5) The persistence of heavy precipitation was related to the long-term maintenance of the 850 hPa dew point front and the surface convergence line caused by the enhancement of cold pool and warm and humid air flow in the boundary layer.