Oceanic Forcings of the Interdecadal Variability in East Asian Summer Rainfall

In this study, it was found that the Pacific decadal oscillation (PDO) and the Atlantic multidecadal oscillation (AMO) are shown to be the two major drivers of the interdecadal variability of summer rainfall over East Asia. The first leading mode (PC1) of this interdecadal variability-associated with an in-phase variation of rainfall anomalies along the Yangtze River valley and Huanghe-Huaihe River valley in China-is attributed to the PDO, while the second leading mode (PC2)-associated with seesawlike rainfall anomalies between the Yangtze River valley and Huanghe-Huaihe River valley-is attributed to the AMO. The AMO teleconnects its influence to the East Asian region, and beyond, through a circumglobal stationary baroclinic wave train extending from the Atlantic Ocean, through the Eurasian continent, and extending to North America. The AMO also altered the nature of the PDO through this atmospheric teleconnection, resulting in the occurrence of a different PDO pattern ("pseudo-PDO'') between the 1960s and 2010s. The pseudo-PDO has a different anomalous SST pattern in both the tropical and midlatitude Pacific compared to the conventional PDO. The pseudo-PDO causes a distinct atmospheric response in East Asia leading to an opposite relationship with the PC1 compared to the conventional PDO, thus leading to a change in the direction of the influence of the PDO on PC1 between the 1880s-1950s and the 1960s-2010s.