Research On Rapid Intensification Tropical Cyclone And Its Relationship With The Vertical Wind Shear Over Westem North Pacific

Base on the analysis of the statistical characteristics of per24h intensity change for TC, We define three different thresholds of tropical cyclone rapid intensification by using the tropical cyclone best track data of Joint Typhoon Warning Center (JTWC) and the NCEP/NCAR reanalysis data from1980to2009. Then, the comprehensive comparison and analysis of the features of rapid intensification TC are given in different thresholds.Finally,we pay attention to the study on the rapid intensification of Songda(2011), based on which we successful simulated the track and sea level pressure. Results showed that:We define the thresholds of tropical cyclone rapid intensification as25kt,30kt,35kt, which respectively represent the different methods of24-h overwater intensity changes of tropical cyclones in the Northwest-Pacific area. The maximum probability of TCs undergoing RI emerges during September and in initial intensity of65-70kt. And, most of tropical cyclones undergo RI in the region with the center as (12.5°N,130°E).When the environmental vertical wind shear from200hPa to850hPa is between2-6m/s, tropical cyclones can undergo RI easily. When vertical wind shear appers southeast (northwest), the number of tropical cyclones undergo RI is largest (fewest).According to zonal wind shear between200hPa and850hPa, we divide the vertical wind shear (WS) into the westerly vertical wind shear (WWS) and easterly vertical wind shear (EWS).Compare the characteristics of rapid intensification of tropical cyclones in EWS with that in WWS, the results show that about70%of RITCs occur in EWS.The maximum probability of TCs undergoing RI emerges during September and in initial intensity of65-70kt.In large EWS, the transport of abundant vapor is from southwest at850hPa. At500hPa, the Pacific subtropical anticyclone appears strong and large. The ridge line of subtropical high is situated above the25th degree of Northern Latitude. The temperature at outflow layer is below-79℃.While in large WWS, the transport of water vapor is from southeast at850hPa. At500hPa, subtropical high is split. Comparing with the former, the divergence field of RITCs at200hPa is weaker. And the temperature at outflow layer is about-76℃. The Weather Research and Forecasting modeling system (WRF) is used to simulate hurricane "Songda".The transport of water vapor is from southeast at925hPa. The rapid intensification of water vapor is favorable for "Songda" to undergo RI process. When the vertical wind shear appears northwest, it is unfavorable for "Songda" to maintain circulation structure. And the RI process of "Songda" is terminated because of large northwest vertical wind shear.