The Climate Characteristic Of Tropical Cyclone Genesisnumber And Its Relationship With Environment Factors In The Western North Pacific

Using a calculation of genesis potential index (GPI) developed by Emanuel and Nolan, based on the tropical cyclone (TC) data from Joint Typhoon Warning Center (JTWC) and the monthly reanalysis data provided by the European Center for Medium-range Weather Forecasts (ECMWF), the TC genesis number and climatology of GPI in the western North Pacific (WNP) for the period of1970-2001were compared. The influence of TC frequency of the spatial distribution interannual and interdecadal changes on the various environment factors and sea surface temperature (SST) of the different seas on climate changes in WNP was analyzed. Obtaining the following main conclusion:(1) The distribution of TC genesis frequencies all have two centres in JASO in the WNP:one centre in the southeast of South China near the15°N,115°E,the other centre in the east of Philippine Islands near the15°N,130°E. It generate TC separately:0.8and0.7in average every year.The seasonal changes of GPI is consistent with TC genesis frequencies in the WNP,Both of climatic field of spatial distribution similarity coefficient is0.75.The climatic field of GPI only have one centre of the high value in the east of Philippine Islands.There is no centre of the high value in South China.(2) There is the apparent interannual and interdecadal changes of the TC frequency in the WNP,the interdecadal variability greater than the interannual.1989-1997is the most active decade, generating21.7in average every year., more than1975-1973(15.8one/year),6one/year.The positive anomaly of the spatial distribution of interdecadal changes of the TC frequentcy in the WNP scatter primarily the east of130℉.The largest of the positive anomaly of TC frequencies center near (15°N,140°E) is affected by the positive anomaly of the absolute vorticity and relative humidity.The abnomal variation of the vertical wind shear lead to TC frequencies positive anomaly near (10°,160°E). Each of environmental factors impact on the TC frequency that have significant difference. The TC intensity is stronger,the relation humidity is weaker;The vertical wind shear is opposite; Absolute vorticity is the most significant influence on TC genesis frequencies.(3) The linear correlation analysis show that TC genesis frequencies in the WNP with the tropical eastern and central Pacific(Indian Ocean and Atlantic Ocean)sea surface temperature anomaly have the positive(negative)relation significantly. The tropical eastern and central Pacific of the key sea area of warm years and cold years of the environment factors composition show that the absolute vorticity is positive anomaly in the east of Philippine Islands and the southeast of South China, The vertical wind shear is negative anomaly near (20°,130°E).The SSTA of the tropical eastern and central Pacific mainly through affect the absolute vorticity and the vertical wind shear anomaly influence on TC genesis frequencies of the east of Philippine Islands. The Indian Ocean of the key sea area of cold years and warm years of the environment factors composition show that the absolute vorticity is the most significant in the South China,in favor of TC generating.The Atlantic Ocean of the key sea area SSTA of negative lead to the relative humidity and the vertical wind shear anomaly in the east of160°E. It makes the TC genesis frequencies of the region increase.