Large-Scale, Low-Frequency Variability in Wind-Driven Ocean Gyres

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Abstract
The authors investigate the spontaneous occurrence of large-scale, low-frequency variability of steadily forced, two-gyre, wind-driven circulations. The model dynamics is quasigeostrophic, the density stratification is represented in 1.5- and 2-layer approximations, and the wind stress pattern is either asymmetric or symmetric about the midbasin. The authors show that more generic variability arises when the forcing is strongly asymmetric, the Reynolds number is relatively large, and the baroclinic instability mechanism is active. The variability is explored for a wide range of values for the viscosity coefficient, that is, the Reynolds number. The regimes include steady circulation, periodic and quasiperiodic fluctuations near the beginning of the bifurcation tree, and chaotic circulations characterized by a broadband spectrum. Both the primary and secondary bifurcation modes and the spatiotemporal patterns within certain frequency bands in the chaotic regime are analyzed with an EOF decompositi... Abstract The authors investigate the spontaneous occurrence of large-scale, low-frequency variability of steadily forced, two-gyre, wind-driven circulations. The model dynamics is quasigeostrophic, the density stratification is represented in 1.5- and 2-layer approximations, and the wind stress pattern is either asymmetric or symmetric about the midbasin. The authors show that more generic variability arises when the forcing is strongly asymmetric, the Reynolds number is relatively large, and the baroclinic instability mechanism is active. The variability is explored for a wide range of values for the viscosity coefficient, that is, the Reynolds number. The regimes include steady circulation, periodic and quasiperiodic fluctuations near the beginning of the bifurcation tree, and chaotic circulations characterized by a broadband spectrum. Both the primary and secondary bifurcation modes and the spatiotemporal patterns within certain frequency bands in the chaotic regime are analyzed with an EOF decompositi...

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