Remote Influences of ENSO and IOD on the Interannual Variability of the West Antarctic Sea Ice

Abstract

West Antarctica exhibits a pronounced sea ice variability in interannual timescale, and 20%-30% of the total variance can be explained by the El Nino-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) during austral spring. The sea ice variation is primarily linked with anomalous atmospheric circulation in the Amundsen-Bellingshausen Sea (ABS) that modulates poleward atmospheric temperature advection and radiative forcing. With a co-varying relationship between ENSO and IOD, isolating their remote impacts on Antarctica has been limited in observations. An idealized experiment using the atmospheric model with a dry dynamical core suggests that the anticyclonic circulation anomaly in the ABS is primarily contributed by the ENSO in the Pacific Ocean, while the contribution of the IOD in the Indian Ocean is only one-third large. This study implies that atmospheric teleconnection through the southern Pacific Ocean is crucial for understanding the West Antarctic sea ice concentration variability.Plain Language Summary Antarctic sea ice, which affects the Earth's climate system, has gained considerable attention in recent years. Previous studies have shown that the El Nino-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) in the tropics affect the sea ice variation in West Antarctica through atmospheric teleconnections at interannual timescale. Unfortunately, due to the high positive correlation between these two climate modes, it is unclear how each phenomenon contributes to the West Antarctic sea ice variation. Therefore, this study investigates the underlying mechanisms related to the sea ice changes caused by ENSO and IOD during austral spring and quantifies the effect of each phenomenon on the West Antarctic sea ice through an idealized model experiment. It is found that the ENSO and the IOD account for 20%-30% of sea ice variance during austral spring, which is primarily contributed by the dynamic and thermodynamic mechanisms associated with atmospheric circulation in the Amundsen-Bellingshausen Sea (ABS). In addition, we confirm through the model experiments that the effect of ENSO in the Pacific Ocean on the atmospheric circulation patterns of ABS is about three times stronger than that of IOD in the Indian Ocean.