Asian Precipitation Changes in the Past Millennium: Projection of Volcanic Forcing Onto Internal Mode

Abstract Asian precipitation changes over multiple time scales have been extensively studied, yet the relative roles of external forcing and internal variability in shaping the large‐scale Asian precipitation pattern over the past millennium remain underexplored. Here, we demonstrate that the tripolar pattern of decadal precipitation variability across South Asia, southeastern Asia, and northern East Asia in the past millennium is primarily driven by the Interdecadal Pacific Oscillation (IPO) but is modulated and synchronized by external volcanic forcing. Volcanic aerosol forcing stimulates IPO‐like sea surface temperature (SST) anomalies that influence Asian precipitation through mechanisms similar to those from the internal IPO. Nonetheless, volcanic forcing effect is distinguishable from the IPO due to subtle differences in the resulting large‐scale SST and atmospheric circulation anomalies. These anomalies, induced by interhemispherically asymmetric external forcing, differ from the IPO's more symmetric patterns and provide a pathway to differentiate the internally generated and the externally forced climate variations.