Analysis of the warm shear-type rainstorm process in the middle reaches of the Yangtze River influenced by the Northeast China cold vortex and the Southwest China vortex

During the Meiyu season in China, in addition to the continuous systematic precipitation typically triggered by the stationary shear of the Meiyu front, there are also strong precipitation events caused by other types of weather systems, among which is warm shear-type precipitation. Using multi-source observational data from the Integrative Monsoon Frontal Rainfall Experiment (IMFRE-II) in 2020, an analysis was conducted of a strong precipitation event occurring in the middle and lower reaches of the Yangtze River from June 27th to 29th, 2020. The results indicate that: (1) This rainstorm process was a warm shear-type precipitation influenced by the eastward movement of the Southwest China vortex under the background of the Northeast China cold vortex. The peak of precipitable water vapor (PWV) occurred approximately 1-2 hours earlier than the peak of heavy precipitation. (2) Strong southwest low-level jets (exceeding 30 m·s^-1) intersected with the cold air from North China in the middle reaches of the Yangtze River, generated the warm shear line on the left side of the low-level jet exit. The rainstorm area was located on the south side of the shear line, with a deep upward motion zone present, providing dynamic lifting conditions for heavy precipitation. (3) The South China Sea provided the maximum water vapor supply, and moisture transport formed a significant moisture convergence zone in the middle and lower reaches of the Yangtze River. CAPE values at Yichang station reached up to 1806 J kg⁻¹, and pseudo-equivalent potential temperatures (θ_se) exceeded 355 K on June 27th, indicating vigorous convection development and providing strong thermal conditions for heavy precipitation. It is hoped to deepen the forecasters' understanding of the formation mechanism of such rainstorm and play a positive role in improving the extreme precipitation forecast level.