Interannual variability in the Southern Ocean from an ocean model forced by European Centre for Medium-Range Weather Forecasts reanalysis fluxes

Anomaly patterns in the Southern Ocean in response to variability in the atmospheric forcing are investigated. To this end we forced the Hamburg large-scale geostrophic ocean general circulation model with surface fluxes from the European Centre for Medium-Range Weather Forecasts reanalysis (ERA). ERA covers the period January 1979 through February 1994. First, the atmospheric variability of sea level pressure and the associated wind stress anomalies within the ERA data set are analyzed. An Antarctic Circumpolar Wave type pattern is identified. In the ocean response, sea water temperature and salinity anomalies are found to vary with similar periods. The anomalies advect with the Antarctic Circumpolar Current. High amplitudes occur in the southeast Indian and Pacific Oceans. Sensitivity studies are made, pinning down wind stress and heat flux as the dominant factors generating these anomalies. The oceanic interannual variations are explained in terms of enhanced oceanic convection resulting from anomalous Ekman pumping and anomalous heat fluxes, both operating in a standing pattern dominated by wavenumbers 2 and 3.