Decadal-Multidecadal Variations Of Asian Summer Rainfall From The Little Ice Age To The Present

Features of decadal-multidecadal variations of the Asian summer rainfall are revealed by analysis of the reconstructed Asian summer precipitation (RAP) dataset from 1470 to 2013. Significant low-frequency periodicities of the all-Asian rainfall (AAR) index (AARI) are found on decadal (8-10 yr), quasi-bidecadal (22 yr), and multidecadal (50-54 yr) time scales, as well as centennial time scales. The decadal and multidecadal peaks are mainly from the "monsoon Asia" area and the Maritime Continent, while the 22-yr peak is from the "arid Asia" area. A remarkable change of leading frequency from multidecadal to decadal after AD 1700 is detected across the entire Asian landmass. The leading empirical orthogonal function (EOF) modes on the decadal and multidecadal time scales exhibit a uniform structure similar to that on the interannual time scale, suggesting a cross-time-scale, in-phase variation of the rainfall across continental Asia and the Maritime Continent. Enhanced AAR on a decadal time scale is found associated with the mega-La Nina sea surface temperature (SST) pattern over the Pacific. The AARI-mega-ENSO (El Nino-Southern Oscillation) relationship is persistently significant except from 1820 to around 1900. Enhanced decadal AAR is also found to be associated with extratropical North Atlantic warming. The AARI-AMO (Atlantic multidecadal oscillation) relationship, however, is nonstationary. On the multidecadal time scale, the AAR is significantly related to the AMO. Mechanisms associated with the decadal-multidecadal variability of AAR are also discussed.