On the Vacillation of an Unstable Baroclinic Wave Field in an Eddy-Resolving Model of the Oceanic General Circulation

Abstract

The vacillation of baroclinically unstable waves in a two-layer eddy-resolving oceanic circulation model is described. The vacillation cycle is distinguished kinematically by the mutual coexistence at equilibrium of short (60-day) period mesoscale eddies and a well-defined long (480-day) period modulation to the larger scale flow, as well as the long-term mean ocean circulation. Global energy budgets and related linear stability analyses reveal underlying systematic energy transfers between the slowly varying mean and transient fields of motion. The vacillation phenomenon is shown to occur over a rather narrow range of the nondimensional model parameters. Since the vacillation occurs in the presence of ?, a highly structured mean flow field and meridional boundaries, this is perhaps the most complicated geophysical flow situation in which a vacillation cycle has been clearly observed.