PDI オ モチイタ タイフウ キョウド ノ トウケイテキ カイセキ ニ ミル チキュウ カンキョウ ノ ヘンドウ

Power dissipation index (PDI) in the tropical depression and the mean sea surface temperature (SST) on the western North Pacific Ocean are calculated, analyzed and compared statistically. The data sources are from JTWC and the Met Office Hadley Centre for PDI and SST evaluation, respectively. Smoothed chart shows that the mean SST in a year is increasing continuously with the averaged gradation of 0.0190 Celsius degree/year since 1977. This may suggest an appearance of some phase in global climate change. Annually accumulated PDI of tropical depression increase apparently after the 1985. However, maximum wind power of these tropical depression is slightly decreasing since 1973, in spite of the super typhoon development was supposed. According to the data analyses of tropical depression, it is revealed that the PDI increasing might be caused by life time extending of the tropical depression. Especially, the average life span of typhoon after 1972 is about 1.4 times longer than those of before the year. Frequency of tropical depression formation is gradually increasing. It is also notable that this frequency change continues about 31 years of period. However, ratio of the tropical storm to the typhoon tend to be larger than 1.0 since 1980. This seems consistent to the result of PDI analysis