The paper describes the mean ocean circulation and tropical variability simulated by the Max Planck Institute for Meteorology (MPI-M) coupled atmosphere–ocean general circulation model (AOGCM). Results are based on a version of the model used as a prototype for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) simulations. The model does not require flux adjustment to maintain a stable climate. A control simulation with present-day greenhouse gases is analyzed, and key oceanic features such as sea surface temperatures (SSTs), large-scale circulation, meridional heat and freshwater transports, and sea ice are compared with observations. A parameterization that accounts for the effect of ocean currents on surface wind stress is implemented in the model. The largest impact of this parameterization is in the tropical Pacific, where the mean state is significantly improved: the strength of the trade winds and the associated equatorial upwelling weaken, and there is a reduction of the model's equatorial cold SST bias by more than 1 K. Equatorial SST variability also becomes more realistic. The strength of the variability is reduced by about 30% in the eastern equatorial Pacific and the extension of SST variability into the warm pool is significantly reduced. The dominant El Niño–Southern Oscillation (ENSO) period shifts from 3 to 4 yr. Without the parameterization an unrealistically strong westward propagation of SST anomalies is simulated. The reasons for the changes in variability are linked to changes in both the mean state and to a reduction in atmospheric sensitivity to SST changes and oceanic sensitivity to wind anomalies. The model's mean state is compared with observations, and the simulation of tropical interannual variability is presented. The impacts of the new wind stress parameterization on the mean state and on interannual variability are described. The model's mean state shows improvements in the tropical Pacific, including a reduction in the cold SST bias and a more realistic representation of equatorial SST variability. The model's simulation of the annual cycle of equatorial SST shows a weak semiannual cycle in the west and a strong westward-propagating annual cycle in the east. The model's simulation of the Niño-3 index shows a reduction in variability compared to the NWSC run, but the standard deviation of the simulated SSTs is still roughly 0.5 K higher than the respective ones from HadISST. The spectral peak of the WSC Niño-3 time series is shifted from 3 to 4 yr, closer to the 4–6-yr band that characterizes the dominant ENSO period in the observations. The model's simulation of the annual cycle of equatorial SST is characterized by a weak semiannual cycle in the west and a strong westward-propagating annual cycle in the east. The model's simulation of the Niño-3 index shows a reduction in variability compared to the NWSC run, but the standard deviation ofThe paper describes the mean ocean circulation and tropical variability simulated by the Max Planck Institute for Meteorology (MPI-M) coupled atmosphere–ocean general circulation model (AOGCM). Results are based on a version of the model used as a prototype for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) simulations. The model does not require flux adjustment to maintain a stable climate. A control simulation with present-day greenhouse gases is analyzed, and key oceanic features such as sea surface temperatures (SSTs), large-scale circulation, meridional heat and freshwater transports, and sea ice are compared with observations. A parameterization that accounts for the effect of ocean currents on surface wind stress is implemented in the model. The largest impact of this parameterization is in the tropical Pacific, where the mean state is significantly improved: the strength of the trade winds and the associated equatorial upwelling weaken, and there is a reduction of the model's equatorial cold SST bias by more than 1 K. Equatorial SST variability also becomes more realistic. The strength of the variability is reduced by about 30% in the eastern equatorial Pacific and the extension of SST variability into the warm pool is significantly reduced. The dominant El Niño–Southern Oscillation (ENSO) period shifts from 3 to 4 yr. Without the parameterization an unrealistically strong westward propagation of SST anomalies is simulated. The reasons for the changes in variability are linked to changes in both the mean state and to a reduction in atmospheric sensitivity to SST changes and oceanic sensitivity to wind anomalies. The model's mean state is compared with observations, and the simulation of tropical interannual variability is presented. The impacts of the new wind stress parameterization on the mean state and on interannual variability are described. The model's mean state shows improvements in the tropical Pacific, including a reduction in the cold SST bias and a more realistic representation of equatorial SST variability. The model's simulation of the annual cycle of equatorial SST shows a weak semiannual cycle in the west and a strong westward-propagating annual cycle in the east. The model's simulation of the Niño-3 index shows a reduction in variability compared to the NWSC run, but the standard deviation of the simulated SSTs is still roughly 0.5 K higher than the respective ones from HadISST. The spectral peak of the WSC Niño-3 time series is shifted from 3 to 4 yr, closer to the 4–6-yr band that characterizes the dominant ENSO period in the observations. The model's simulation of the annual cycle of equatorial SST is characterized by a weak semiannual cycle in the west and a strong westward-propagating annual cycle in the east. The model's simulation of the Niño-3 index shows a reduction in variability compared to the NWSC run, but the standard deviation of