An Interdecadal Oscillation in an Idealized Ocean Basin Forced by Constant Heat Flux.

Abstract The authors report on a regular, interdecadal oscillation in a three-dimensional ocean circulation model. The model is run using box geometry of size comparable to the North Atlantic and is driven by a constant, zonally uniform, surface heat flux. The meridional overturning in the model exhibits a peak to peak oscillation of 7 Sv about a mean of 15 Sv. The period is 50 years. The oscillation has many similarities to that found by Delworth et al. in the GFDL coupled ocean-atmosphere model. In particular, the SST anomaly pattern during the oscillation. is quite similar to that in the coupled model and also to interdecadal anomaly patterns seen in SST data from the North Atlantic. Since the surface flux is constant, the oscillation is due to a balance between convergence in the oscillating part of the poleward heat transport and changes in local heat storage. A similar balance applies to the coupled model where changes in surface heat flux weakly oppose the oscillation. Including salinity, by adding...