A Statistical Analysis on the Eect of Vertical Wind Shear on Tropical Cyclone Development

Using tropical cyclone (TC) best track and intensity of the western North Pacic data from the Joint Typhoon Warning Center (JTWC) of the United States and the NCEP/NCAR reanalysis data for the period of 1992-2002, the eects of vertical wind shear on TC intensity are examined. The samples were limited to the westward or northwestward moving TCs between 5N and 20N in order to minimize thermodynamic eects. It is found that the eect of vertical wind shear between 200 and 500 hPa on TC intensity change is larger than that of the shear between 500 and 850 hPa, while similar to that of the shear between 200 and 850 hPa. Vertical wind shear may have a threshold value, which tends to decrease as TC intensies. As the intensifying rate of TC weakens, the average shear increases. The large shear has the obvious trend of inhibiting TC development. The average shear of TC which can develop into typhoon (tropical depression or tropical storm) is below 7 m s1 (above 8 m s1). Key words: vertical wind shear, tropical cyclone (TC), statistical analysis 1