South Pacific circulation changes and their connection to the tropics and regional Antarctic warming in austral spring, 1979–2012

Abstract

AbstractAfter 1979, statistically significant warming in Antarctica is only observed in austral spring (September–November, SON) across West Antarctica and the Antarctic Peninsula. While previous work has linked this warming to reductions in sea ice cover, we note that a substantial (30–60%) portion of the warming is related to changes in the SON atmospheric circulation. In particular, western Antarctic Peninsula warming is consistent with increasing pressure in the South Atlantic, while western West Antarctica warming is tied to a deepening of the Amundsen Sea low near the eastern Ross Sea. While both of these circulation changes are associated with increased warm, northerly flow toward the Antarctic continent, they are connected with different aspects of tropical variability. The increase in pressure in the South Atlantic is associated with a trend toward more La Niña‐like conditions in the tropical Pacific, and an associated Rossby wave train. In contrast, the deepening of the Amundsen Sea low is more strongly tied to a shift in the Pacific Decadal Oscillation (PDO) toward its negative phase since the 1990s. Compared to typical La Niña events, the recent negative PDO events display a different tropical forcing, which drives a Rossby wave train that propagates more meridionally across the South Pacific, culminating in the eastern Ross Sea, rather than in the South Atlantic. The results suggest multiple independent forcing mechanisms governing the SON pressure trends and associated Antarctic Peninsula and West Antarctica warming after 1979, which partially cancel each other out in the Amundsen Sea and portions of eastern West Antarctica.