Evolution Feature of the Rainy Season Onset Time of Yunnan Province
云南雨季开始期演变特征分析

Applying EOF method,Morlet Wavelet Method and 42-year precipitation data of 16 representative stations in Yunnan province daily from 1961 to 2002 to research the spatial distribution,temporal evolution and multi-scale period of the rainy season onset time of Yunnan Province.The results indicated that: 1) The firstly main spatial distributive feature of the rainy season onset time in Yunnan was that the whole province's rainy season onset time was unanimously earlier(or later) than the normal time;The secondly main spatial distributive feature of the rainy season onset time in Yunnan was that it was reverse spatial distribution between the middle,the eastern and the southern areas of Yunnan and the western areas of Yunnan;2) There was obviously approximately 40a long oscillation period,approximately 28 a interdecadal oscillation period and approximately 8-year interannual oscillation period.It could be seen from wavelet variance that the 40-year and 28-year period were the strongest and most remarkable among the periods of rainy season onset time in Yunnan and interannual change period is relatively weaker;3) There was an obviously difference of 500 hPa anomalous height field in May between above-normal and below-normal years of rainy season in Yunnan;4) India monsoon and south sea of China monsoon had positive effect on the rainy season onset time in Yunnan.