Phenomenology of the low-frequency variability in a reduced-gravity, quasigeostrophic double-gyre model

Abstract The low-frequency variability of the oceanic wind-driven circulation is investigated by use of a reduced-gravity, quasigeostrophic model with slight variations on the classic double-gyre wind forcing. Approximately 30 eddy-resolving simulations of 100–1000 years duration are analyzed to determine the types of low-frequency variability and to estimate statistical uncertainties in the results. For parameters close to those leading to a stable antisymmetric solution, the system appears to have several preferred phenomenological regimes, each with distinct total energy levels. These states include a high-energy quasi-stable state; a low-energy, weakly penetrating state; and a state of intermediate energy and modest eddy/ring generation. The low-frequency variability of the model is strongly linked to the irregular transitions between these dynamical regimes. For a central set of reference parameters, the behavior of the system is investigated for each period in which the total energy remains in certa...