东亚夏季PJ遥相关型的年际及年代际变化机理

利用夏季东亚地区500 h Pa高度场和菲律宾附近的降水场进行SVD分析,将东亚500 h Pa高度场对应的时间序列定义为PJ指数,该指数不仅清楚地反映PJ型的年际变化,而且反应出PJ型的年代际变化,即500 h Pa高度场型态在20世纪70年代末由"气旋、反气旋、气旋"型突变为"反气旋、气旋、反气旋"型。本文研究表明PJ指数的年际变化与ENSO事件有密切的联系:El Ni1o事件通过电容器充电效应使印度洋海温增暖,而增暖的印度洋海温在菲律宾海附近强迫出异常反气旋,并沿东亚沿岸激发出PJ遥相关型。而PJ型态的年代际变化与热带印度洋SST的持续增暖有关。虽然许多学者认为是菲律宾附近海温异常引起对流异常,并沿东亚沿岸激发出PJ遥相关型,但我们认为该区域的海温变化并不是造成PJ型年际和年代际变化的原因,而是由于该区域有反气旋(或者气旋)异常,从而辐射增加(减少),蒸发减弱(增加),温跃层下降(上升),SST变暖(变冷),该区域的海温变暖意味着对流是减弱的。本文进一步利用大气环流模式ECHAM5.4进行数值试验,结果表明:当热带印度洋增暖时,在菲律宾海附近强迫出反气旋,并沿东亚激发出"反气旋、气旋、反气旋"PJ遥相关型。

The interannual and interdecadal variation mechanism of the summer PJ teleconnection pattern in East Asia

A new PJ index is introduced by using the singular value decomposition(SVD) method at the 500 hPa height field in summer in East Asia as well as in precipitation field near the Philippines.This time series/index can clearly reflect the PJ interannual and interdecadal variations,which were demonstrated by the 500 hPa height switching from "cyclone,anticyclone,cyclone" to "anticyclone,cyclone,anticyclone" in the late 1970s.This study also shows that the interannual variation of the PJ index is closely related to the El Niño Southern Oscillation(ENSO) event.El Niño teleconnection makes the Sea surface temperature(SST) in tropical Indian Ocean(TIO) increase like a battery charging a capacitor,and the increased temperature leads to the formation of abnormal anticyclones near the Philippine Sea.In addition,ENSO events also stimulate the PJ teleconnection pattern along the coast of East Asia.Moreover,the interdecadal variation of PJ patterns is related to the continuous increasing TIO SST.Many researchers have proposed that SST anomalies near the Philippine Sea result in anomalous convection and stimulate the PJ teleconnection pattern along the coast of East Asia.However,we have concluded that variations of SST in this area are not the reason for the interannual and interdecadal variations of the PJ pattern.Instead,these variations result from the TIO SST anomalies.The SST anomalies over the Philippine Sea are caused by the NW Pacific anticyclone,thus the radiation increases(decreases),the evaporation decreases(increases),the thermocline deepens(shoals) and the SST becomes warmer(colder).The increased SST in this area corresponds to weakened convection.Furthermore,numerical simulations by using the atmospheric circulation model ECHAM5.4(European Centre Hamburg Model5.4) show that when the TIO SST increases,anticyclones are produced near the Philippine Sea and stimulate the "anticyclone,cyclone,anticyclone" PJ teleconnection pattern along the coast of East Asia.