Solar Irradiance Modulates the ENSO- Asian Summer Monsoon Teleconnection over the Past Millennium

The Asian summer monsoon (ASM) plays a critical role in supplying freshwater resources to more than one-third of the world’s population, with significant environmental, societal, and economic impacts. The ASM is influenced by the El Niño Southern Oscillation (ENSO) through atmospheric and oceanic teleconnections, yet the relationship between ASM and ENSO is nonstationary and has undergone notable changes in recent decades. Understanding the drivers of these changes in the ENSO-ASM teleconnection is essential for improving ASM prediction. Previous studies based on individual paleoclimate proxy records have revealed a coherence between ASM intensity and solar activity on multidecadal to centennial timescales. However, twentieth-century instrumental data are too short to test the influence of solar irradiance on the ENSO-ASM relationship and the underlying mechanisms. This work quantifies the impact of solar irradiance on the ASM-ENSO relationship using last-millennium paleoclimate data assimilation reconstructions (the Last Millennium Reanalysis and Paleo Hydrodynamics Data Assimilation products) and model simulations (Community Earth System Model Last Millennium Ensemble). We find during periods of high solar irradiance, the correlation between ENSO and the East Asian summer monsoon declines, whereas the correlation between ENSO and the South Asian summer monsoon strengthens. Further analysis suggests that solar irradiance influences the strength of the ENSO-ASM teleconnection through both 1) alterations in dominant subtropical pressure systems and 2) the amplitude of ENSO events. This study provides robust, paleoclimate-derived evidence characterizing the modulation of the ENSO-ASM teleconnection by solar irradiance. We further explored the relative impacts of solar irradiance and anthropogenic forcings, like greenhouse gases and aerosols, to assess how solar irradiance will compound with these radiative changes in the 21st century and impact the ENSO-ASM teleconnection. Explicitly including and further quantifying the impact of solar activity is critical for improving the decadal prediction of ASM rainfall under future global warming scenarios.