https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2025GL118463
*Authors: *Wenmin Man, Bo Wu, Tianjun Zhou, Wenhui Tang, Meng Zuo First published: *03 March 2026* https://doi.org/10.1029/2025GL118463 *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. *Plain Language Summary* The Asian summer monsoon exhibits robust decadal variations, while both external forcing agents and internal variability are suggested as potential drivers, it remains unclear how the interplay of external forcing and internal variability modulates the Asian monsoon, partly due to the time length limitation of instrumental data. Here, based on the reconstruction data and climate model simulations of the past millennium, we find that the leading interdecadal precipitation variability mode spanning South Asia, Southeast Asia, and northern East Asia is primarily driven by low-frequency variability associated with the Interdecadal Pacific Oscillation (IPO). Moreover, external forcing, primarily from volcanic aerosols, can trigger similar precipitation patterns by altering sea surface temperatures and atmospheric circulation in ways that resemble IPO-driven changes. Despite these similarities, externally forced responses to volcanic aerosols exhibit distinguishable features, including hemispheric asymmetries, which differ from the more symmetric structure of the internal IPO. These findings provide insights into how external volcanic aerosol forcing influences regional climate through mechanisms like those from the internal variability mode. They also have important implications on how Asian precipitation may respond to *climate interventions such as stratospheric aerosol injection.* *Key Points* The leading decadal Asian precipitation mode is primarily driven by the Interdecadal Pacific Oscillation (IPO) but modulated by volcanic aerosol forcing The externally forced change of Asian precipitation is projected onto the leading internal variability mode of IPO A novel mechanism that connects volcanic forcing, IPO phase transition, and IPO-Asian precipitation teleconnection is proposed Source: AGU -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/geoengineering/CAHJsh98kgmWKkTOu5-605ndwUeOB0tORiOvs1-A_cgqvzOOekg%40mail.gmail.com.
