Latitude-Dependent Response of East Asian Summer Monsoon to External Forcing in the Last Millennium

Response of the East Asian summer monsoon (EASM) rainfall to external forcing (insolation, volcanic aerosol, and greenhouse gases) is investigated by analysis of a millennium simulation with the coupled climate model ECHO-G. The model reproduces reasonably realistic present-day EASM climatology. The simulated precipitation variation in East Asia over the last millennium compares favorably with the observed and proxy data. It is found that the features and sensitivity of the forced response depend on latitude. On the centennial-millennial time scale (CMTS), the extratropical precipitation closely follows the variation of the effective radiative forcing (insolation plus radiative effects of volcanic aerosols). The subtropical precipitation is less sensitive but the differences of this variable between the Medieval Warm Period (MWP) and Little Ice Age (LIA) remain significant. The tropical rainfall is insensitive to the external forcing. It is also found that the precipitation variations in the extratropics and subtropics are in phase on the CMTS, while they are anti-correlated on the interannual time scale. The intertropical convergence zone (ITCZ) and subtropical precipitation are anti-correlated on the CMTS, so are they on the interannual time scale. These findings suggest that the proxy data in the extratropical East Asia more sensitively reflect the EASM variations, and this has important implications on interpretation of paleo-proxy records.