Wintertime Arctic Sea Ice Decline Related to Multi-Year La Niña Events

Arctic sea ice has undergone a significant decline in the Barents–Kara Seas since the late 1990s. Previous studies have shown that the decrease in sea ice caused by increased poleward moisture transport is modulated by tropical sea temperature changes (mainly referring to La Niña events). The occurrence of multi-year La Niña events has increased significantly in recent decades, and their impact on Arctic sea ice needs to be further explored. In this study, we investigate the relationship between sea ice variation and different atmospheric diagnostics during multi-year La Niña and other La Niña  years. The decline in BKS sea ice during multi-year La Niña winters is significantly stronger than that during other La Niña years. It is because the multi-year La Niña tends to accompany the warm Arctic-cold continent pattern with a barotropic high-pressure blocked over the Ural region. Consequently, more frequent northward atmospheric rivers intrude into the BKS, intensifying long-wave radiation downward to the underlying surface and melting sea ice in the Barents–Kara Seas. However, in the early mature winter of other La Niña cases, negative North Atlantic Oscillation presents in the North Hemisphere high latitudes, which obstructs the atmospheric rivers to the south of Iceland. We infer that such a different response of sea ice decline in Barents–Kara Seas to different La Niña is related to stratospheric processes. Considering likely future climate change, more frequent multi-year La Niña events may account for substantial Arctic sea ice loss in recent decades. In particular, it was proposed that the multi-year La Niña probably occur more frequently in a warming climate.