The Modulation Of Environmental Intraseasonal Oscillation For Tropical Cyclone Precipitation In Eastern China

Using the data of tropical cyclones(TCs)best-track data from China Meteorological Administration(CMA)of Shanghai Typhoon Research Institute,national 753 stations daily precipitation data and NCEP environmental data during 1985-2015 JJA,the ISO index of the Northwest Pacific(WNP)region is defined on the basis of the daily variation of the Intraseasonal Oscillation(ISO)of the latitudinal wind in the troposphere.The propagation characteristics of 30-60 and 10-20-day oscillations under the East and west wind phases and their effects on WNP TCs activities are analyzed.According to the regional precipitation generated by the TCs landing process,TCs is divided into three categories:the diagnosis of the environmental anomaly characteristics affecting the TCs precipitation and the modulation effect of ISO on it.The main conclusions are as follows:1)ISO has distinct propagation characteristics in different phases.In the westerly wind phase,the 30-60-day ISO anomaly moves northward,generating more TCs and the number is about two times of the easterly phase which is beneficial to the formation of TCs in the exuberant convection area,and the landfall TCs is concentrated in the anomalous cyclonic convergence center or the negative OLR anomaly center,and the landing TCs is dominated by the northwest path.The 10-20-day ISO abnormal is westward moving.The number of TCs and the number of TCs landings are more.TCs moves in the direction of northwestern.In the easterly phase,the 30-60-day-ISO-anomalies still move northward,the TCs generation is less, the landing TCs is shifted to the northward path,and the 10-20-day abnormal moves northwestern,and there is no significant difference between the number of TCs and the TCs landing number with the westerly phase and the northwest route is the main route.2)For the strong rainfall type,a cyclonic anomaly center near eastern of Fujian in China that causes strong moisture supply from the bay of bengal and the South China Sea(SCS),and strong moisture convergence result in heavy rainfall in southeast coast of china.both 30-60-day and 10-20-day ISO of circulation and water vapor transport are contributed to it,but moisture convergence in southeast coast of china mainly influenced by 10-20-day ISO.For strong rainfall,both 10-20-day and 30-60-day ISO of persistent enhanced cyclonic anomaly propagate northwestward from Philippines to southeast coast of china and northeast--ward/northerm from the SCS to westsouthern of Taiwan in the process of TCs landfall.3)In contrast,the heavy rainfall TCs landfalling in Southern China is not only decreasing from the coast to the inland but also from the south to the north,but the 850 hPa cyclone anomaly center is located in the north of the South China Sea.The strong water vapor convergence which from the bay of Bengal,the South China Sea and the Northwest Pacific Ocean produces strong TCs precipitation.And the contribution of 10-20-day ISO is relatively greater.The 10-20 day ISO circulation anomaly spread northwest from the south of Philippines to the northwest of Guangdong during TCs landfalling,and the 30-60-day ISO anomalous cyclone remained in the north of the South China Sea.