A Shifting Tripolar Pattern of Antarctic Sea Ice Concentration Anomalies During Multi‐Year La Niña Events

Abstract

AbstractA 2,200‐year CESM1 pre‐industrial simulation is used to contrast Antarctic sea ice concentration (SIC) variations between the first and second austral winters of multi‐year La Niñas. The typical SIC anomaly pattern induced by single‐year La Niñas appears only during the second austral winter of multi‐year La Niñas. A similar pattern, but zonally shifted compared to the typical one, is found during the first winter and exhibits a tripolar pattern with anomaly centers over the Ross, Amundsen‐Bellingshausen, and Weddell Seas. The shift is a result of the pre‐onset conditions associated with multi‐year La Niñas that excites unique atmospheric circulation modes during the first winter. The distinct zonally‐shifted SIC anomaly pattern is observed in four of the six multi‐year La Niña events during the period 1979–2020. These results suggest that it is helpful to separate La Niñas into single and multi‐year events to better understand the La Niña impacts on Antarctic climate.