Periodic Characteristics and Cause Analysis of Continuous Heavy Rainfall Induced by Typhoon Yagi (1814) in Shandong

The Best Track from China Meteorological Administration (CMA) tropical cyclone database as well as the observation data of high level and surface stations, minute precipitation, radar, satellite and reanalysis data were used to analyze both periodic characteristics and cause of continuous heavy rainfall induced by the “north going” landing Typhoon Yagi(1814) in Shandong. The results show: During the period under the influence of Yagi, the torrential rain has distinct phases. The precipitation of typhoon body and the cold air and typhoon interaction are much stronger than those of two other stages. The precipitation formed by the typhoon body has larger range but weaker intensity than that of the heavy rain phase when the cold air interacted with the typhoon. The typhoon body precipitation phase has low-centroid tropical precipitation features, while the cold air and typhoon interaction phase shows high-centroid frontal precipitation features. During the northward movement of Yagi, the water vapor transport conditions were significantly abnormal compared with those of normal years, which was favorable for persistent heavy rainfall. During the typhoon body precipitation stage, the main heavy precipitation area is located in the forward direction of the typhoon, while in the cold air interacted with the typhoon stage, the main heavy precipitation area is located in the direction of the typhoon and the spiral rain band on the right side of Yagi. The top of low-level jet, vertical wind shear in the low and middle troposphere and convergence line above ground surface together determine where the main heavy precipitation area occurs. The moving direction of typhoon is consistent with both the long axis direction of isentropic potential vorticity (IPV) and the moving direction of high value center of IPV. During the typhoon movement, the IPV has a significant increase, which is caused by the transfer from the higher-level atmosphere that has high potential vorticity (PV) cold air to the lower level atmosphere. During the later period of Yagi landfall, the spiral rain band developed, while the mesoscale convection characteristics were significant. This is related to frontogenesis induced by the cold air invasion as well as high-altitude terrain. On the one hand, the frontogenesis in the cold air and typhoon interaction phase is obvious. On the other hand, the high-altitude terrain in the central and eastern regions of Shandong which plays an uplifting role and the frontogenesis of the weather system are conducive to the convective system enhancement, therefore promote the spiral rain band to develop.（This paper has been published in Plateau Meteorology）