四川冕宁山区一次强降水天气过程分析

Analysis of the Weather Process of a Heavy Rainfallin the Mianning Mountains of Sichuan

基于卫星、风廓线雷达、加密自动站等观测资料及ERA5再分析资料,采用天气学诊断分析方法,对2020年6月26日四川省冕宁地区一次致灾性强降水过程进行诊断分析。结果表明:1)此次强降水过程是冷空气作用下多尺度天气系统和复杂地形相互作用的结果,尺度小、突发性强。2)降水发生在前倾槽形势下,槽后弱冷平流叠加在低层西南暖湿气流之上,形成“上冷下暖”的不稳定层结。过程中副热带高压与南亚高压相向而行,中低层冷空气沿四川盆地自北向南推进,与两个高压之间阶段性增强的西南暖湿气流交汇,西南涡随之先减弱后增强并东移,不断被触发对流云团,最终形成“列车效应”,从而导致降水显著增强。3)暴雨带分布和雨团活动与MCS发展演变存在关联。雷暴冷出流、地面冷空气、复杂地形三个因素在强降水云团的触发、组织和发展过程中起到了重要作用,而中低层冷空气侵入与西南涡强弱变化及降水起止时间有较为明显的对应关系。

Based on the observation data from satellite,wind profile radar,data collected at regional automatic weather stations and ERA5 reanalysis data,a disaster-causing heavy rainfall process in Manning of Sichuan Province on June 26,2020 was diagnosed and analyzed using the method of synoptic diagnosis and analysis.The results were as follows:1)The heavy rainfall was caused by the interaction between multi-scale weather systems and terrain under the influence of cold air,with small scale and strong sudden occurrence.2)The precipitation occurred in a forward inclined trough situation,where the weak cold advection behind the trough was superimposed on the low-level southwest warm and humid airflow,forming an unstable stratification of“upper cold and lower warm”.When precipitation occurred,the subtropical high and the South Asian high moved in opposite directions,and the cold air in the middle and lower layers advanced from north to south along the Sichuan Basin,intersecting with the gradually enhanced southwest warm and humid airflow between the two high layers.The southwest vortex weakened,then strengthened,and moved eastward.The newly formed convective cloud clusters were constantly stimulated,forming a“train effect”that enhanced the precipitation.3)The distribution of rainstorm was related to the development and evolution of MCS.Thunderstorm cold outflow,surface cold air,and complex terrain played an important role in the triggering,organization,and development of heavy precipitation cloud clusters.The beginning and end of precipitation presented a good correspondence between the change of cold air in the middle and low levels and the variation of the southwest vortex.