The Effects Of Vertical Wind Shear On Tropical Cyclone Intensity Of Variation In Northwestern Pacific

Using tropical cyclone (TC) best track and intensity data of Northwestern Pacific from theJoint Typhoon Warning Center (JTWC) of U.S.A. and the NCEP/NCAR Reanalysis data, theeffects of vertical wind shear on TC intensity of interannual as well as interdecadal variation areexamined. The characteristic of large-scale parameters on TC activity is analyzed from verticalwind shear, SST, low-level relative vorticity and mid-level in troposphere moisture, in recentlydecade landing typhoon of Northwestern Pacific. Three typhoons (Bills, Chanchu, Saomai) arechosen to analyze the effects of vertical wind shear on TC intensity in the whole process. ModelWRF is used to model the typhoon Bilis in statistical analysis. The main results are as follow:(1)There is contrary change trend of time between maximum wind speed and environmentalvertical shear. The weak environmental vertical shear is propitious to the development of tropicalcyclones. (2)The most impact of environmental vertical shear to intensity change of tropicalcyclones, the intensities of which are above tropical storm in the Northwestern Pacific, appears a12 h time lag. (3)In space, when TC is strong the environmental vertical shear is small, and thereare more tropical cyclones; when TC is weak the environmental vertical shear is large, and thereare few tropical cyclones. (4)The SST is higher in more tropical cyclones region than others,besides the SSTs are above 26.5℃; low-level relative vorticity is nearly positive and mid-levelmoisture in troposphere is larger, which are in favor of the development of tropical cyclones.(5)It's reasonable that using Model WRF to model the path of TC, but there are some errors forair pressure on sea level. There is same change trend of time between TC center lower airpressure and environmental vertical shear.