TEMPORAL VARIABILITY OF THE WIND-DRIVEN QUASI-GEOSTROPHIC DOUBLE GYREOCEAN CIRCULATION - BASIC BIFURCATION DIAGRAMS

In this paper we explore how temporal variability arises through succe ssive bifurcations of the symmetric wind-driven double gyre circulatio n as lateral friction is decreased in 1.5-layer and 2-layer quasi geos trophic models. In the 1.5-layer model, the symmetric double gyre flow becomes unstable to symmetry breaking stationary instabilities, leadi ng to asymmetric flows. These asymmetric solutions subsequently destab ilize to two sets of barotropic oscillatory modes, introducing an inte rmonthly and interannual time scale, respectively. In the 2-layer mode l, the symmetric double gyre solution becomes unstable to baroclinic o scillatory instabilities, giving rise to near annual temporal variabil ity. The asymmetric solutions which appear through symmetry breaking a t smaller lateral friction, are in this case all unstable.