关键词: 台风, 极端暴雨, 葵花8号, 水汽图像, 大气可降水量

Abstract:

We analyzed the formation of an extreme rainstorm event over the Chaoyang area in the western region of Liaoning province and the Xiuyan County in the Southeastern Peninsula, caused by the typhoon "Haitang" in 2017, mainly using the conventional observation data, Final (FNL) reanalysis data from National Center of Environment Prediction (NCEP), Himawari-8 satellite data, Precipitable Water Vapor (PWV) retrieved from Global Navigation Satellite Systems (GNSS), and real-time products in smart grids.The results indicated that regional extreme heavy rainstorms occur in both of the western regions of Liaoning province and the Southeastern Peninsula.The Xiuyan County has larger hourly precipitation, with the maximum precipitation reaching 113 mm per hour, which shows obvious characteristics of convective precipitation.The rainstorm processes in both regions are influenced by systems from the tropical and subtropical zones and the westerlies.Typhoon "Haitang", showing a long and narrow shape, gradually moves northward along the western side of the Subtropical High, and interacts with a short wave trough of the westerlies, which results in the heavy precipitation in the western region of Liaoning province.Subsequently, dry cold air behind the strengthened vortex system interacts with warm and moist air in the low altitudes, leading to the extreme rainstorm event in Xiuyan County.Tropical typhoon "Aolu" blocks the retreat of the Subtropical High.Both regions have water vapor channels from the South China Sea, and the Southeastern Peninsula is also affected by the water vapor transport from the northern side of Typhoon "Aolu".The PWV in Chaoyang and Xiuyan almost reaches 65 mm and 70 mm in a long time period, respectively, and the maximum anomaly index is approximately 3.0 and 2.5, indicating the extreme condition for water vapor loading in the atmosphere during this rainstorm process.The dynamic instability is stronger in the western region of Liaoning province during the precipitation period.The convergence layer extends from the ground up to 500 hPa.The "upper dry and lower wet" distribution of water vapor in the Southeastern Peninsula and the stronger convergence of cold and warm air are more favorable to forming the convective precipitation.Multi-mesoscale clouds also affect the precipitation processes in both regions.The precipitation in Chaoyang County is caused by cumulus triggered by a meso-γ-scale convergence line during the early period, thereafter, the continuous heavy precipitation is related to the cold-front cloud system and the warm-front cloud system that is due to the interaction between the northward-moving typhoon and dry, cold air behind an upper trough.The intruding of dry air in the rear of the strengthened vortex into the transport belt of warm and wet water vapor is combined with a stable convergence line over the Xiuyan mountain area, which makes cumulus trigger continuously and directly affect the Xiuyan County and results in the extreme convective rainstorm in this region.

Key words: Typhoon, Extreme heavy rainstorm, Himawari-8 satellite, Water vapor imagery, Precipitable water vapor (PWV)