Analysis on Dynamic Diagnostic before and after Typhoon’Morakot’ Landing

Using the GFS(Global Forecast System) analytical data with 0.5°×0.5° grid intervals,the NCEP reanalysis data with four times a day and the satellite cloud image data,the evolution characteristic before and after the typhoon 'Morakot' landing with No.8 are dynamically analyzed.Based on the diagnostic analysis of tendency equation of disturbed potential vorticity,the result shows that: Firstly,there exists centers of tangential wind near typhoon center at mid-and low-levels which lead to the intensive area of the horizontal flux divergence of potential vorticity located on the inner side of the center of tangential wind.Secondly,the negative and positive horizontal flux divergences of potential vorticity at low levels can be employed as a pointer for forecast the typhoon moving on the sea.Thirdly,the intensive areas of negative vertical flux divergence of potential vorticity offer reference for forecast of typhoon moving under the p coordinate.Finally,by using the vorticity equation,the principal determinants of the variation of the cyclone vorticity at mid-and low-levels are discussed.Meanwhile,the important coupling effect of typhoon and southwest low-level jet in coastal region of the South China Sea and Southern China on the structure and routine of this typhoon are also investigated.