On the mechanism of the Antarctic circumpolar wave

The variability in the subpolar Southern Hemisphere is studied with a coupl ed atmosphere-ocean-sea-ice model (the ECBilt). After having reached an app roximate statistical equilibrium in coupled mode without flux corrections, a subsequent 1000-yr integration is performed and analyzed. A singular Valu e decomposition of austral winter SST anomalies and 800-hPa geopotential he ight in the Antarctic Circumpolar Current region reveals a mode of covariab ility that resembles the observed Antarctic circumpolar wave. Subsequent an alysis of this mode shows that it is basically an oscillation in the subsur face of the ocean. Additional experiments suggest that it is generated by t he advective resonance mechanism: the oscillation is excited by the dominan t modes of variability in the atmosphere, whereas the timescale is set by t he ratio of the horizontal scale of these atmospheric modes and the advecti on velocity of the mean oceanic currents. The atmospheric response mainly c onsists of a local temperature adjustment to the SST anomaly, which reduces the damping of the SST anomalies. Salinity, wind stress, and sea-ice anoma lies do modify the structure and intensity of the mode without playing an e ssential role.