Diagnostic Analysis of Coupling Effect between Tibetan Plateau Vortex and Southwest China Vortex Inducing Heavy Rainstorm

Based on the ground station observation data, ERA5 reanalysis data and global precipitation data GPCP, this paper takes the regional heavy rainstorm caused by the coupling of Tibetan Plateau Vortex and Southwest China Vortex on June 4-7, 2019 as an example to diagnose and analyze the coupling characteristics and formation mechanism of precipitation. The results show that: (1) The weather process was caused by the combined action of plateau vortex and southwest vortex, and the precipitation developed explosively from night to early morning. On June 4, the two vortices produced precipitation centers in the northwest and southwest respectively, and the precipitation was in the center and rear of the vortex. The two vortices were coupled in the early morning of May 5 to 6, and the precipitation moved to the front of the vortex to strengthen and reach the peak. The center of the heavy rainstorm was in the north of Hubei Province. On the night of 6, the two vortices moved eastward out of the sea, and the precipitation area disappeared on land. (2) During the evolution of the two vortices, it was found that when the plateau vortex moved eastward from the plateau, the divergence term and the vertical transport term enhanced the positive vorticity of the basin. At the same time, with the strengthening of the low-level convergence configuration, the southwest vortex was further induced to form in the basin, and precipitation occurred in the two vortex regions, which provided a key dynamic condition for the subsequent coupling of heavy rain. (3) During the coupling development, the centers of the two cyclones at different heights merged to form a deep convective system, which stimulated strong positive vorticity columns and strong convective instability, accompanied by vertical upward motion and secondary circulation development. The southwest monsoon and the southerly airflow outside the subtropical high transport abundant water vapor to the front of the vortex, and under the synergistic effect of deep shear convergence and strong dynamic uplift, it eventually leads to heavy rain.