Causes and meso-scale characteristics of the short-duration rainstrom in Nanchang on 29 June 2022

With the Meiyu front rain belt weakened toward the south during June 26 to 29, 2022, the rainfall in Jiangxi was significantly strengthened on June 29. A narrow and strong regional rainstorm belt appeared in the north of Jiangxi, especially in the main urban area of Nanchang, where the rainfall for 2 h exceeded 100 mm (the maximum hourly rainfall was 113.2 mm), which caused severe waterlogging. Based upon the conventional observation data, ERA5 reanalysis data, Fengyun meteorological satellite data, and Doppler weather radar data, this study attempts to analyze the causes, mesoscale characteristics, and maintenance mechanism of this short-duration rainstorm in the Nanchang city. The results show that before the rainstorm occurred, the low-level (850 hPa) southwest jet in Jiangxi weakened apparently, while the water vapor and energy increased. From 08:00 BT on the 28th to 08:00 BT on the 29th, the dew point, the total precipitable water, and the temperature of Nanchang increased from 23.5℃, 57.5 mm, and 76℃ to 26℃, 69 mm, and 81℃, respectively, which led to the occurrence and development of convective heavy precipitation. The sustained strong divergence at the upper-level, the intrusion of dry and cold air at 600-800 hPa, and the strong convergence of water vapor in the boundary layer triggered by the enhancement of 925-975 hPa boundary layer jet were the main causes of the rainstorm. At the beginning of rainstorm, the convective echo located in northeast Jiangxi had obvious backward propagation characteristics. It combined with the eastward echo of northwest Jiangxi in Nanchang and then developed rapidly. After the combination, new convective cells were generated continuously on the south and southwest sides of the strong echo zone, moving and converging to the northeast, resulting in the stagnation of strong echo in Nanchang. Convective cells were regenerated on the convergence line between the cold pool outflow and the ambient atmosphere. The convergence lines over the northeast and northwest of Jiangxi located on the west and east of the convection zone, respectively. The two convergence lines moved to the opposite directions and met in Nanchang, leading to the rapid development of echo. The development of echo enhanced the cold pool, and the outflow of cold pool strengthened the rise of the warm and humid air that promoted the development of echo and formed a positive feedback, which was the maintenance mechanism of strong echo in Nanchang.