The Effect Of Environmental Field On Intensity Of Typhoon In The Northwestern Pacific

The characteristics of landing typhoon in China is analyzed with global warming, and the differences between the characteristics of landing typhoons in China and the ones of typhoons in the Northwestern Pacific are studied, and tropical cyclogenesis and its development in the Northwestern Pacific are examined through the two parameters of vertical wind shear and low level vorticity by using the NCEP four-time/day reanalysis and monthly mean data for wind field from 1951 to 2002 ( the horizontal resolution of 2.5°x2.5°lat./lon. grid ) , and Typhoon Year-book from 1949 to 1984 and Tropical Cyclone Year-book from 1985 to 2002 extracted from China Meteorological Administration, and the global surface temperature. The main results are as follows: 1) With global warming, the decreasing trend of frequency of typhoon landing in China is weaker than that occurring in the Northwestern pacific, and that average and extreme intensity of typhoon landing in China are both lessening, especially the later, but decreasing trend are weaker than that of typhoon occurring in the Northwestern pacific. In the global warming period of 1968—2002, the landing position of typhoon landing in China situated toward the middle of China and the position of typhoon in the Northwestern Pacific has the trend to the north when it is strongest during its life. 2) The formation potential area of typhoon in the Northwestern Pacific is closed to the zero vertical zonal wind shearing regions and the negative ones, in the same time, the zero line of vertical zonal wind shear is closed to shear line of between east wind and west wind in 850hp and the west of zero wind shear line is in favor of tropical cyclogenesis because of west wind in bottom level and east wind in upper level, that is to say that the wind shear value of the west of zero wind shear line is negative and that topical cyclones have a tendency to occurin the negative vertical wind shear environment, and the east of zero wind shear line, vice verse. 3) The negative or weak wind shear is beneficial to typhoon development, while the great positive one is adverse to typhoon development;in the same time, vertical wind shear has a delay effect of -1.25-5.5 day on the strongest intensity in typhoons' life, and the delay time has a weak ascending trend in the period of 1951—1977 and a weak decreasing trend in the period of 1978—2002.