The influences and mechanisms of external forcings, e.g., volcanic eruptions, anthropogenic aerosols, and solar radiations, on two aspects of decadal climate changes, decadal climate variability (i.e., PDO and AMO) and decadal megadroughts over the eastern China were investigated using model simulations from the observations, proxy reconstructions, Community Earth System Model (CESM) Last Millennium Ensemble (LME) archive, Coupled Modeling Intercomparison Project phases 5&6 (CMIP5&6) archives, and Paleoclimate Modeling Intercomparison Project phase 3 (PMIP3) archive.  The influences from external forcings and internal variability on PDO, AMO, and AMOC are first differentiated through several groups of sensitivity experiments.  Then, systematic assessments of model simulations showed that models can reproduce similar frequency, durations, and magnitudes with the reconstructed megadroughts, but not temporal synchronous, indicating that the internal variability trigger the megadroughts.  Moreover, the combined influences from external forcings and internal variability on decadal megadroughts are also investigated.  For example, nonlinear responses of the precipitation variability to the large-scale atmospheric circulation patterns induce more larger megadrought frequencies during LIA and MCA.  While, the volcanic forcing sensitivity experiments produce fewer megadroughts than the reconstruction and control simulation.  A case study of Ming Dynasty megadrought showed that this drought is a typical drought triggered by internal variability and strengthened by the volcanic eruption, and this intensification is stronger during the late stage of droughts.
 

paleoclimate modeling, decadal climate changes, climate dynamics