Analysis on the formation mechanism of heavy precipitation in Liaoning Province caused by northward-moving tropical cyclone "Bavi"

The precipitation characteristics and the formation mechanism of heavy precipitation in Liaoning Province in different stages caused by the northward-moving tropical cyclone (TC) "Bavi", are analyzed based on the routine observations, the Doppler radar data, the tropical cyclone data from the Central Meteorological Observatory, the numerical model prediction data, and the global reanalysis data. The results are shown below. (1) The heavy precipitation in Liaoning Province can be divided into three stages: the stage of long-distance influence by the TC, the stage of outer spiral rainband influence by the TC, and the stage of TC body influence. In the first two stages, convective heavy precipitation occurred in Liaoning Province. In the second stage, the convective intensity was weaker than that in the first stage, while in the third stage, stable precipitation occurred in Liaoning Province with weak intensity. (2) The northward movement of TC "Bavi" provided continuous transport of water vapor and energy for precipitation in Liaoning Province. Dry and cold air effect and frontogenesis forcing were present in both the long-distance and outer spiral rainband influence stages. The strong frontogenesis developed in Liaoning Province due to the warm and moist air transported by the TC. Through frontogenesis forcing, vertical convection was formed under the convective instability in the first stage, and inclined convection was formed under moist symmetric instability in the second stage, respectively, which led to convective heavy precipitation being generated in both stages. At the stage of TC body influence, the TC degraded rapidly, and Liaoning Province was located at the west side of TC, where both thermal and dynamic forces weakened significantly. At the same time, it lacked proper cold air, and frontogenesis developed weakly, resulting in weak precipitation. (3) The heavy precipitation area in the stage of outer spiral rainband influence corresponded to the strong frontogenesis area at 850 hPa that is certainly indicative for forecasting of precipitation caused by the TC.