The East Asian summer monsoon (EASM) experienced dramatic interdecadal changes during the latter half of the 20^th century. The interdecadal changes of the EASM have been attributed to tropical SST forcing, the weakening of atmospheric heating over the Tibetan Plateau; the global warming caused by the increasing concentrations of greenhouse gases (GHGs) in the atmosphere; and the increased level of air pollution over the East Asia.  

Importantly, most of the above-mentioned studies focused on the latter half of the 20^th century, primarily due to the rich observational and reanalysis data available for this period. However, there are two problems that are inevitably hard to address due to the relatively short time span. First, it is difficult to distinguish the interdecadal variability of the EASM internally generated in the climate system from its response to external forcing. Second, it is difficult to identify whether a forcing factor responsible for the interdecadal change of the EASM is an internal fluctuation of the climate system or an external forcing. 

Based on the 20^th century reanalysis (20CR) dataset, Drs. WU Bo and ZHOU Tianjun Zhou from LASG/IAP tried to extend the study of the interdecadal variability of the East Asian summer monsoon to the 1920s. For the longer period, the signals associated with the global warming and internally generated variability can be separated via a regression method. They revealed that the interdecadal variability of the East Asian summer monsoon is associated with the two famous large-scale atmospheric teleconnection patterns, the Pacific-Japan (PJ) and circumglobal teleconnection (CGT) patterns. The interdecadal PJ and CGT patterns are associated with the two dominant interedecadal variability modes of the climate system, the interdecadal Pacific oscillation (IPO) and the Atlantic multi-decadal oscillation (AMO), respectively. 

Therefore, it’s concluded that the interdecadal PJ and CGT patterns are consistent with their interannual counterparts on atmospheric dynamical features, but exhibit shifts in spatial phases.    

Citation: Wu Bo, Tianjun Zhou, Tim Li, 2016. Impacts of the Pacific-Japan and circumglobal teleconnection patterns on interdecadal variability of the East Asian summer monsoon. Journal of Climate, 29, 3253-3271. http://journals.ametsoc.org/doi/10.1175/JCLI-D-15-0105.1

Contact: WU Bo, wubo@mail.iap.ac.cn