On the Mechanism of the Antarctic Circumpolar Wave

Abstract

The variability in the subpolar Southern Hemisphere is studied with a coupled atmosphere?ocean?sea-ice model (the ECBilt). After having reached an approximate statistical equilibrium in coupled mode without flux corrections, a subsequent 1000-yr integration is performed and analyzed. A singular value decomposition of austral winter SST anomalies and 800-hPa geopotential height in the Antarctic Circumpolar Current region reveals a mode of covariability that resembles the observed Antarctic circumpolar wave. Subsequent analysis of this mode shows that it is basically an oscillation in the subsurface of the ocean. Additional experiments suggest that it is generated by the advective resonance mechanism: the oscillation is excited by the dominant modes of variability in the atmosphere, whereas the timescale is set by the ratio of the horizontal scale of these atmospheric modes and the advection velocity of the mean oceanic currents. The atmospheric response mainly consists of a local temperature adjustment to the SST anomaly, which reduces the damping of the SST anomalies. Salinity, wind stress, and sea-ice anomalies do modify the structure and intensity of the mode without playing an essential role.