A Case Study of One Local Severe Convection Process Caused by Meso‐β‐Scale Vortex in a Forming Southwest China Vortex in Spring With Large Eddy Simulation

Abstract The fifth generation of ECMWF atmospheric reanalyses data (ERA5), operational observed data, S‐band radar data and Large Eddy Simulation (LES) tool were employed to investigate the evolution of local small‐scale convection in Ziyang City of Sichuan Province on 11 April 2022 in spring. The meso‐β‐scale vortex and 700‐hPa wind shear in the Sichuan Basin horizontally merged and formed the Southwest China vortex. The local convection induced heavy rainfall, hail and thunderstorm in the northeast of the organizing meso‐β‐scale vortex. The well‐developed meso‐β‐scale vortex became the center of Southwest China vortex. The horizontal scale and time scale of the meso‐β‐vortex were 20–50 km and 2–3 hr, respectively. The newly formed convections over the northeast of the meso‐β‐scale vortex developed in the middle troposphere and quickly separated from the main body of the meso‐β‐scale vortex with the guided airflow. The convective organization at the northeastern forepart of the meso‐β‐scale vortex was reproduced in LES results. The strong convection and meso‐β‐scale vortex were basically activated in the same period. The significant isobaric surfaces for strong convection formation were from 750 to 500 hPa. And cold air in the middle and lower troposphere rarely affected the convective process. Local convections were mainly triggered by strong vertically meridional wind shear.