RELATIONSHIPS BETWEEN PACIFIC DECADAL OSCILLATION (PDO) AND CLIMATE VARIABILITIES IN CHINA

Relationships between Pacific Decadal Oscillation (PDO) and atmospheric circulation in East Asia and climate variabilities in China are investigated by using statistical method.The regression coefficient supon the PDO index time series during period 1951~1998 are computed for a number of related oceanic and atmospheric variables and the observed surf ace air temperature and precipitation at 160 stations in China.The results exhibit that the relationships are sig nificantly remarkable.It is considered that the PDO is in its warm phase,i.e.,negative SST anomaly in the North Pacific and positive anomaly in the center to eastern tropical Pacific.Accordingly,during winter,Aleutian Low tends to be much lower than normal while Mongolian High appears much stronger (but Siberian High is weaker).Associated with this,northeastern,northern China and Yangtze River valley are drier;northwestern,northeastern and northern China are warmer while southwestern China is cooler.During summer,the negative SL Panomalies are much weaker in North Pacific while positive ones are enhanced over East Asia,together with a reduced East Asian summer monsoon,a sout hward shifted Western Pacific Subtropical High and a reduced equatorial trade wind.Resultantly,northern China is much drier while Yangtze River valley and southern,northeastern and northwestern China are wetter;northeastern,northern and southern China are warmer while northwestern and southwestern China and Yangtze River valley are cooler.It is vice versa during the PDO cool phase.It is also found that PDO can modulate the impact of ENSO events on summer climate variability in China.During the PDO cool phase,the onset of an El Niño event acts as to dry southern China and cool northeast China,while the decaying of an El Niño event acts to wetnorthern China and Yangtze River valley and dry Huai River valley.During the PDO warm phase,however,the onset of an El Niño event coincides with wet southern China,dry northern China and warm northeast China,while the decaying of an El Niño event coincides with dry northern China,increasingly wet Yangtze River valley and normal Huai Rivervalley.