太平洋年代际振荡与中国气候变率的联系

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

利用 195 1～ 1998年的太平洋年代际振荡 (PDO)指数、全球海洋和大气分析资料及中国降水和气温站点观测资料 ,分析了太平洋年代际振荡在海洋中的特征及其与东亚大气环流和中国气候变率的联系。结果表明 ,PDO与东亚大气环流及中国气候年代际变化关系密切。对应于PDO暖位相期 (即中纬度北太平洋异常冷、热带中东太平洋异常暖 ) ,冬季 ,阿留申低压增强 ,蒙古高压也增强 (但东西伯利亚高压减弱 ) ,中国东北、华北、江淮以及长江流域大部分地区降水偏少 ,东北、华北和西北地区气温异常显著偏高 ,而西南和华南地区气温偏低 ;夏季 ,海平面气压在北太平洋的负异常较弱 ,而在东亚大陆的正异常较强 ,东亚夏季风偏弱 ,西太平洋副热带高压偏南 ,热带太平洋信风减弱 ,赤道西风增强 ,此时华北地区降水异常偏少而长江中下游、华南南部、东北和西北地区降水异常偏多 ,东北、华北及华南地区气温异常偏高 ,而西北、西南和长江中下游地区气温异常偏低。对应于PDO冷位相期 ,上述形势相反。结果还表明 ,处于不同阶段的ENSO事件对中国夏季气候异常的影响明显受到PDO的调制。在PDO冷位相期 ,当ENSO事件处于发展阶段 ,华南地区夏季降水偏少 ,东北地区夏季多低温 ,在其衰减阶段 ,华北地区和长江流域降水偏多 ,淮河地区降水偏少 ;?

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 coefficients upon the PDO index time series during period 1951～1998 are computed for a number of related oceanic and atmospheric variables and the observed surface air temperature and precipitation at 160 stations in China. The results exhibit that the relationships are significantly 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 SLP anomalies are much weaker in North Pacific while positive ones are enhanced over East Asia, together with a reduced East Asian summer monsoon, a southward 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 Nio event acts as to dry southern China and cool northeast China, while the decaying of an El Nio event acts to wet northern China and Yangtze River valley and dry Huai River valley. During the PDO warm phase, however, the onset of an El Nio event coincides with wet southern China, dry northern China and warm northeast China, while the decaying of an El Nio event coincides with dry northern China, increasingly wet Yangtze River valley and normal Huai River valley.