Understanding the interdecadal variability of East Asian summer monsoon precipitation: Joint influence of three oceanic signals
Journal of Climate, (Apr 10, 2018)DOI: 10.1175/jcli-d-17-0657.1
Abstract
East Asian summer monsoon precipitation (EASMP) features complicated interdecadal variability with multiple time periods and spatial patterns. Using century-long datasets of HadISST, CRU precipitation and ERA-20C reanalysis, this study examines the joint influence of three oceanic interdecadal signals, i.e., Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), and Indian Ocean Basin Mode (IOBM), on the EASMP, which, however, is found not to be simply a linear combination of their individual effects. When PDO and AMO are out of phase, the same sign SST anomalies occur in North Pacific and North Atlantic, and a zonally-orientated teleconnection wave train appears across the Eurasian mid-high latitudes, propagating from North Atlantic to northern East Asia along the Asian westerly jet waveguide. Correspondingly, the interdecadal precipitation anomalies are characterized by a meridional tripole mode over eastern China. When PDO and AMO are in phase, with opposite sign SST anomalies in North Pacific and North Atlantic, the sandwich pattern of anomalous stationary Rossby wavenumber tends to reduce the effect of the waveguide in the eastern Mediterranean, and the teleconnection wave train from North Atlantic travels only to the western central Asia along a great circle route, causing Indian summer monsoon precipitation (ISMP) anomalies. The ISMP anomalies in turn interact with the teleconnection wave train induced by the PDO and AMO, leading to a meridional dipole mode of interdecadal precipitation anomalies over eastern China. Through the impact on the ISMP, the IOBM exerts significantly linear modulation on the combined impacts of PDO and AMO, especially over the northern East Asia.