2020 年“8.11”四川芦山极端强降水特征及成因分析

Characteristics and Synoptic Mechanism of the "August 11" Super Historical Extreme Precipitation Event in Western Sichuan Basin

利用地面观测降水、FY2G卫星云图、多普勒雷达数据和ERA-interim再分析资料,对2020年8月11日雅安芦山极端强降水的动力、热力、水汽输送等异常特征进行分析,探究了此次极端强降水的成因,并构建了强降水概念模型。结果表明:此次极端强降水发生在南亚高压脊线北抬、高原低槽东移加强的过程中,具有累计雨量大、突发性强、集中度高等极端性特征,槽前强盛的正涡度平流造成深厚的上升运动,边界层侵入弱冷空气和深厚的湿对流,致使降水效率偏高且强度偏大。边界层辐合线在高温高湿的环境中触发强不稳定能量,中尺度对流系统在弱的环境风条件下稳定少动,芦山上游对流单体“列车效应”导致强辐合的稳定维持,以及对流层中低层偏东风与山脉正交产生的地形增幅作用,共同导致了此次远超历史极值的极端强降水发生发展。

Using surface precipitation data,radar data and ERA(ECMWF Re-Analysis)-Interim reanalysis datasets,the extreme precipitation process in Lushan,Ya'an on August 11,2020(abbreviation as"08.11")is analyzed from the conditions of dynamic,thermal and water vapor anomalies.The results show that:The extreme precipitation occurredin the process of the northward uplift of the South Asian high pressure ridge line and the eastward strengthening of the plateau trough,with the extreme characteristics of large cumulative rainfall,strong suddenness and high concentration.Strong positive vorticity advection in front of the trough caused strong upward motion.There was no obvious cold air during extreme precipitation,which was a rainstorm in warm area with high precipitation efficiency.The convergence line of boundary layer triggered strong uplift under the combination of high temperature,high humidity and strong unstable energy.During the heavy precipitation process,the wind speed from low level to high level was small.Under the condition of weak wind,the small and medium-sized system MCC was stable and less dynamic,it provided continuous power and water vapor environment for extreme precipitation.Banded echoes were constantly generated form Lushan to Tianquan,the stability of"upwind area"made Lushan Storm Column maintain and strengthen,the wind speed in the middle and lower troposphere was orthogonal to the mountains,which enhances the increasing effect of terrain on precipitation.