四川盆地一次持续性暴雨的降雨特征和环流异常分析

Rainfall Characteristics and Circulation Anomaly Analysis of a Persistent Rainstorm in Sichuan Basin

利用四川盆地逐小时雨量资料和ERA5再分析资料,分析了2020年8月10~18日盆地西部持续性暴雨过程的降雨特征和大气环流异常情况。结果表明:本次持续性暴雨过程具有总量大、历时长、雨强强的特征,日雨量、小时雨量均表现出显著极端性,强降雨多发生在海拔从500 m陡升至2000 m的迎风坡一侧40 km范围内。偏东、偏强的南亚高压和偏西、偏强的副热带高压稳定少动,高空槽东移南压受阻挡后与高原槽叠加持续影响四川,为持续性暴雨提供了有利环流背景。孟加拉湾是水汽的主要来源地,持续且极端偏强的水汽供应为持续性暴雨的产生提供支持。过程前期大气层结处于对流不稳定状态,热力作用显著;过程中后期热力作用减弱,西南涡发展深厚,动力作用增强,涡度和散度特征较历史同期偏强,强的动力条件使暴雨得以持续。

Using hourly rainfall data and ERA5 reanalysis data,the rainfall characteristics and atmospheric circulation anomalies of the persistent rainstorm process in the west of the Basin from August 10 to 18,2020 were analyzed.The following conclusions are ob-tained:The continuous rainstorm process showed the characteristics of long rainfall duration,large cumulative rainfall and strong rainfall.Both daily and hourly rainfall showed significant extremes.Heavy rainfall usually occurred in the 40 km range where the terrain rose steeply from 500 m to 2000 m upwind slope.The east and strong South Asian high and the west and strong subtropical high were stable and less active.After being blocked by the eastward migration and southward pressure,the upper trough overlapped with the plateau trough and continued to affect Sichuan,It provided a favorable circulation background for persistent rainstorm.The Bay of Bengal was the main source of moisture,the continuous and extremely strong water vapor supply supported the continuous rainstorm.The atmospheric junction was in convective instability in the early stage of the process,with significant thermal effect.In the late stage of the process,the thermal effect weakened,the southwest vortex developed deeply and the dynamic effect strengthened,The characteristics of vorticity and divergence were stronger than those in the same period of history,and the strong dynamic conditions led to the occurrence of persistent rainstorms.