A bifurcation study of the three-dimensional thermohaline ocean circulation: The double hemispheric case

Within a low-resolution primitive-equation model of the three-dimensional ocean circulation, a bifurcation analysis is performed of double-hemispheric basin flows. Main focus is on the connection between results for steady two-dimensional flows in a nonrotating basin and those for threedimensional flows in a rotating basin. With the use of continuation methods, branches of steady states are followed in parameter space and their linear stability is monitored. There is a close qualitative similarity between the bifurcation structure of steady-state solutions of the twoand three dimensional flows. In both cases, symmetry-breaking pitchfork bifurcations are central in generating a multiple equilibria structure. The locations of these pitchfork bifurcations in parameter space can be characterized through a zero of the tendency of a particular energy functional. Although balances controlling the steady-state flows are quantitatively very different, the zonally averaged patterns of the perturbations associated with symmetry-breaking are remarkably similar for two-dimensional and three-dimensional flows, and the energetics of the symmetry-breaking mechanism is in essence the same.