The Origin Study of South China Extraordinary Drought from Autumn 1998 to Spring 1999

With application of Singular Value Decomposition (SVD) and statistics method,the study was conducted on the time and space structures and the co-relationship between the Guangxi precipitation from autumn to next Mar.and the 500hPa height field and tropical,north Pacific sea surface temperature field.The results show that the first coupling field clearly reflects the ENSO signal with high correlation,and the second ocean-atmosphere coupling field reflects the good negative correlation between the sea temperature in the east of Japan Sea to be the key area and 500hPa height over the east of 100°E.The sea temperature-height field variation from 1998 was analysed,the 500hPa height field in the mid-high latitude of north Pacific is clearly below normal,and above normal in Asian continent and in the mid low latitude of north Pacific,which attributes to the significant weakening of the eastward cold air.The variation of ENSO in the sea temperature field and the La Nina developing process conform to the sea temperature variation modality of the first coupling field.The later period ocean-atmosphere variation conforms to the second coupling field of the sea temperature and atmosphere.It is concluded that the variation of ENSO and temperature ascent in the east of Japan sea favor the formation of abnormal circulation pattern which is the origin of the south China extraordinary drought at the end of this century.The quantitative monthly precipitation forecast in Guangxi from Aug.1998 to Mar.1999 with SVD method was presented.

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