A Numerical Simulation Study On Typhoon “Fitow”(2013)

In this paper, we use mesoscale model the Weather Research and Forecasting Model WRF 3.5 which use the US National Centers for Environmental Prediction(NCEP)’s global reanalysis data FNL 1° X 1° grid data as the initial field and boundary conditions to 2013 typhoon “Fitow” Case numerical simulation study, the evolution features of large-scale circulation background field, and rainfall diagnostic analysis. The results show that:(1) The model can simulate the strong typhoon "Fitow" and "Danas" double typhoon event well. In the large-scale circulation background, because of the West Pacific Substropical High(WPSH) rise towards northwest, Fitow typhoon moving path by northerly route into west route which landed Shacheng town Fuding City of Fujian province at 01:15 October 7 and typhoon strength weakened rapidly after landing. At the same time, the 24 th typhoon in 2013 in the northwestern Pacific Ocean generated "Danas" accelerated westbound direct airflow beneath the role of WPSH, and gradually close to Fitow. 08 UTC 7 Oct two recent typhoons apart, the minimum relative distance of about 11 longtitude by the distance around. Since then, with the subtropical high moving southeast, "Danas" Typhoon westbound route by turning northward path.(2) The results of the horizontal wind field showed lower level 850 h Pa wind field, the north of Fitow is the easterly jet import area; the high-altitude 200 h Pa, Fitow located east of the entrance to the front of the upper trough southwest jet. This upper level divergence wind field and lower level wind convergence configuration is conducive to development. When "Fitow" typhoon weakened, as "Danas" Typhoon near northward, over the coastal areas of Zhejiang maintain a more powerful easterly airflow. It shares a strong easterly flow of warm energy of the sea to the inland transport of water vapor, which provides ample moisture conditions for sustained heavy rainfall occurs.(3) The southeastern Zhejiang province is also the "Fitow" Typhoon’s maximum cumulative precipitation Center area. In the development process of "Fitow" Typhoon, precipitation mainly in the 12 hours before and 12 h after typhoon landed period, 24 hours cumulative rainfall up to 350 mm.(4) The precipitation process diagnostic analysis showed that, the precipitation concentrated center has upper level divergence – lower level convergence wind configuration. This wind filed structure maintains the pumping action of upper level, while also strengthening the lower level’s atmosphere of convergence upward motion. Strong upward movement of warm air which comes from the ocean makes warm air to the middle and upper troposphere. At the same time, the strong rise in the rotating cyclone zone to further strengthen the pumping action of the atmosphere, in favor of the precipitation process under these dynamic conditions together, southeastern Zhejiang province appeared centuries a rare heavy rainfall.Numerical Simulation of the "Buffett" typhoon event and diagnostic analysis of the evolution of the large-scale circulation background characteristics and rainfall in this study can help us to understand more clearly about "Fitow" Typhoon’s dynamic process, and provide reference for future forecasting and research work.