Abstract:Affected by a rare precipitation system with 16 mesovortices (referred to as MV), a local short-time rainstorm process occurred in Fushun of Liaoning Province on the night of 4 August 2023. In this paper, the formation mechanism of MV and the observation characteristics of MV that produced heavy precipitation are analyzed based on multi-source data such as X-band phased array radar. The results show that Fushun was influenced by the high-level trough and low-level shear line and had the abundant water vapor and low lifting condensation height, which were favorable environmental conditions for short-time rainstorm. When the angle between the convergence line and the isotherm line increased under the strong vertical wind shear, a total of 16 MV were detected by X-band phased array radar. The average duration, thickness and top height of the MV were 17 min, 1.7 km and 3.5 km, respectively. These vortices are low-level shallow MV. There were up to 49 times of heavy precipitation with the rainfall amount reaching 10 mm within 5 min, and the average distance between the heavy precipitation stations and MV was only 6.2 km. There were 44 times of heavy precipitation caused by the first and fourth MV, accounting for 89% of all heavy precipitation. Compared to other MV, the two MV that produced heavy precipitation had a longer lifetime and moving distance, with stronger rotation intensity and greater thickness. The two MV were both generated during the stage where the boundary layer jet was significantly enhanced, the 0-1 km wind vector difference exceeded 15 m·s-1 and the surface temperature was higher than 28℃. In the early stage of the MV, the low-level rotation was even stronger reaching the standard of moderate intensity mesoscale cyclones, with vigorous storm developing above. There was no heavy precipitation near the MV at this time. Subsequently, the rotational speed of the MV diminished, and the storm height rapidly decreased. At this moment, heavy precipitation occurred immediately near the MV. In addition, there was a phenomenon of several weaker MV merging with MV that produced heavy precipitation, which was beneficial for the MV sustainment. In conclusion, the evolution of the position and rotational intensity of MV was crucial for the forecasting of heavy precipitation.