Mechanism studies of atmospheric teleconnections involving Antarctic Dipole Variability

Evidence of atmospheric teleconnections in the Antarctic surface climate has been identified in many studies. However, the mechanisms that might lead to the connectivity of the disparate regions remain unresolved. We investigated the mechanisms responsible for the covariability between the Antarctic Dipole (a dominant mode in the Southern Ocean characterized by opposing anomalies involving surface air and ocean temperature, sea ice and sea level pressure between the Ross/Amundsen Sea and eastern Bellingshausen/Weddell Gyre) and 1) the El Niño-Southern Oscillation (ENSO), 2) the Antarctic Oscillation.

The tropical ENSO signal manifests itself in the Antarctic Dipole through altered heat flux associated with the fluctuations of the regional mean meridional atmospheric circulation. Connected to the El Niño events, reduced (enhanced) storm activity in the Ross/Amundsen Sea (the eastern Bellingshausen/Weddell Gyre) leads to a strengthening (weakening) of the poleward segment of the regional Ferrel Cell and a weakening (strengthening) of the equatorward segment of the regional Ferrel Cell indirectly by 1) changing the meridional eddy heat flux convergence/divergence, and 2) shifting the latent heat release zone. The changes of the regional Ferrel Cell then influence surface climate by modulating the mean meridional heat flux.

The response of the Antarctic Dipole to the Antarctic Oscillation is a consequence of a combination of anomalous heat flux and ice advection. Connected to the high-index polarity of the Antarctic Oscillation, there are 1) an anomalous cyclonic circulation in the southeast Pacific, which leads to an anomalous equatorward (poleward) mean heat flux in the Ross/Amundsen Sea (the eastern Bellingshausen/Weddell Gyre); 2) an increased equatorward ice advection in the Ross/Amunden Sea due to an enhanced Ekman drift towards the equator, and an ice divergence away from both sides of the Antarctic Peninsula.