Numerical Simulation Analysis And Orographic Sensitivity Experiments For The Unusual Track Of Megi(1013)

Using the NCEP1°×1°global reanalysis data and CMA-STI best track dataset for tropical cyclones, numerical simulation analysis and orographic sensitivity experiments of super typhoon "Megi"(1013) with wrf3.2.1model was conducted. To mainly analyze large-scale environment flow, itself dynamic, thermodynamic structure adjustment and the Philippines Terrain will influence the Unusual Track of "Megi". Come to a conclusion of that autumn typhoon forecasts should concern the subtropical high instability, the activities of the Tibetan high, the impact of cold air and the advance or retreat of ITCZ. TC structure adjustment will affect typhoon moving. Terrain can also affect the track of TC. The main conclusions are as follows:Tibetan high enhancement and eastward-moving, result in the development of upper-level trough. Cut off the South China high and subtropical high contact. It make South China high pressure southward along to the Indo-China Peninsula. At the same time, Role of the upper-level trough the northerly current guide the cold air invasion from "Megi" northwest, make it westbound blocked. Cross-equatorial flow northwest movement made the basic flow gradually into southwest airflow. Under the joint action of the cold air and southwesterly flow, TC move to north.400-850hPa deep steering flow or500-700hPa two steering flow guide TC moving. The center of the TC moving easily biased low value area of200-850hPa vertical shear area.With the process of "Megi" sudden northward turning, the strong winds district counterclockwise transfer. Distribution of strong winds near the typhoon center area will affect the moving path of TC. Wind speed enhanced in500hPa indicate the direction of TC. TC move to positive vorticity center of lower levels and negative vorticity center of high-level. Dry cold air into southern China and western South China Sea was one of the reasons lead to "Megi" move northward.. TC center is easy to tend to the direction of low-level strong ascending velocity area.Philippine Islands make westbound TC southerly and have adsorption of northerly moving TC. Terrain will slow down TC movement velocity. TC moving westward will accelerated approach to the Philippine Islands and decelerated away from. The terrain can increase TC low-level wind field distribution asymmetry. Topographic uplift will make the front moisture convergence strengthen when TC approach and the rear moisture convergence strengthen when TC away. The terrain will affect the TC track, but "Megi" Unusual Track is not caused by the Philippine terrain.