Impact of the Winter Southern Indian Ocean Dipole on the Summer Precipitation Pattern of Southern Flood and Northern Drought in China

This study explores the impact of winter sea surface temperature (SST) anomalies in the Southern Indian Ocean on summer precipitation patterns in China, utilizing data from reanalysis sources and Coupled Model Intercomparison Project Phase 6 (CMIP6) models. The results reveal that the Southern Indian Ocean Dipole (SIOD), characterized by contrasting SST anomalies in the northeast and southwest regions, acts as a predictor for Chinese summer precipitation patterns, namely floods in the south and drought in the north. In a positive SIOD event, the southwestern Indian Ocean exhibits warmer SSTs, while the northeastern region remains cooler. A negative SIOD event shows the opposite pattern. During the positive phase of the SIOD, the winter SST distribution strengthens the 850-hPa cross-equatorial airflow, generating a robust low-level westerly jet that enhances water vapor transport to the Bay of Bengal (BoB). These air-sea interactions maintain lower SSTs in the northeastern region, which significantly increase the land-sea temperature contrast in the Northern Hemisphere during spring and summer. This strengthened thermal gradient intensifies the southwest monsoon, establishing a strong convergence zone near the South China Sea and amplifying monsoon-driven precipitation in South China. Additionally, CMIP6 models, such as NorESM2-LM and NorCPM1, which accurately simulate the SIOD pattern, effectively capture the seasonal response of cross-equatorial airflow driven by SST anomalies of Southern Indian Ocean. The result highlights the essential role of cross-equatorial airflow generated by the SIOD in forecasting cross-seasonal precipitation patterns.