Distinctive impacts of single- and multi-year Indian Ocean Dipole events on changes of Antarctic sea ice

Using a nearly 1000-year pre-industrial control simulation from the CESM2 Earth System Model in the CMIP6 archive, we identify positive Indian Ocean Dipole (pIOD) events and categorize them into single-year and consecutive multi-year (two- and three-year) types based on their duration. Direct comparisons between different types are conducted to reveal their impacts on Antarctic spring sea ice and atmospheric circulation. Results show that the sea ice anomaly pattern triggered by pIOD events is strongly duration-dependent. Single-year events lead to a dipole pattern in the West Antarctic, whereas the pattern induced by multi-year events is characterized by eastward shift and meridional expansion of the anomaly centers. The lower tropospheric circulation anomalies, guided by Rossby wave trains, are the key mechanism underlying these differences. Sea ice anomalies are modulated by dynamic processes (Ekman transport and thermal advection) and are closely associated with thermodynamic processes (downwelling shortwave and longwave radiation). Compared with single-year events, multi-year events tend to generate more persistent and stronger Rossby wave trains, which maintain and intensify the pIOD impacts on Antarctic sea ice. Furthermore, quantitative sea ice mass budget analysis reveals that changes in sea ice mass are mainly attributed to dynamic processes, basal melting, lateral melting and snow-to-ice conversion.