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 anomalies in the Southern Indian Ocean on summer precipitation patterns in China, examining data from reanalysis sources and CMIP6 models. The results reveal that the Southern Indian Ocean Dipole (SIOD) — identified by contrasting sea surface temperature anomalies in the northeast and southwest regions — acts as a predictor for China's summer precipitation patterns, marked by floods in the south and drought in the north. In a positive SIOD event, the southwestern Indian Ocean exhibits warmer sea surface temperatures, while the northeastern region is cooler. A negative SIOD event shows the opposite pattern. During the positive phase of the SIOD, the winter sea surface temperature 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. Sea-air interactions maintain lower SSTs in the northeast, which significantly increase the land-sea temperature contrast in the Northern Hemisphere during spring and summer. This heightened contrast intensifies the southwest monsoon, creating a strong convergence zone near the South China Sea and amplifying monsoon-driven precipitation in South China. 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 sea surface temperature anomalies of Southern Indian Ocean. This highlights the essential role of cross-equatorial airflow generated by the SIOD in forecasting cross-seasonal precipitation patterns.