Climate change at interdecadal scale has been attracting more and more attention in recent twenty years. An important change is the one in late 1970s in East Asian summer climate, with weakening monsoon and increasing drought (flood) in North China (Yangtze River valley) since then. 

Recent studies by Prof. WANG Huijun and Dr. ZHU Yali from the Institute of Atmospheric Physics revealed an interdecadal change in the East China summer rainfall in the late 1990s, with increased/decreased rainfall in the Huang-Huai/Yangtze River valley.

They found that in the regional circulation field, the East Asian westerly jet stream (EAWJS) became weaker and located more poleward while the western Pacific subtropical high (WPSH) showed little change.

 Further diagnostic analysis and numerical results showed that the simultaneous phase transition of the Pacific Decadal Oscillation (PDO) contributed significantly to this interdecadal change. The negative-phase PDO could induce weakened and poleward positioned EAWJS by altering the regional atmospheric circulation. The jet related vertical circulation was thus changed, leading to strengthened rising motion over the Huang-Huai River valley and more rainfall there. However, it appeared that the Atlantic warming made insignificant contribution to this interdecadal change in East China and partly counteracted the PDO effect. 

These studies on the late 1990s’ interdecadal change reveal that the PDO phase transition is important for the interdecadal changes of summer rainfall in East China and the EAWJS is a key in linking them. The findings are significant for understanding the mechanisms of the interdecadal climate change in East China.