Lateral open boundary conditions for nested limited area models: A scale selective approach

This paper reviews current approaches to the lateral open boundary condition problem for nested regional primitive equation ocean numerical models and proposes a new approach that considers a scale decomposition of the nesting field variables for the barotropic lateral velocity boundary conditions. The Flather [Flather, R.A., 1976. A tidal model of the north-west European continental shelf. Memories de la Societe Royale des Sciences de Liege 6 (10):141–164] open lateral boundary condition is derived from mass conservation considerations and we use this approach to derive a generalized lateral open boundary condition for barotropic velocities. In addition we do a scale selective decomposition of the generalized Flather obtaining new and general lateral scale dependent boundary conditions. The performance of the new lateral boundary conditions have been evaluated in two kinds of experiments: (1) idealized and (2) realistic frameworks. In the idealized framework, as well as the realistic case, the results confirms that the scale selective open boundary conditions improves the solution almost everywhere but in particular in the shallow depth parts of the model domain. In the realistic case the assessment is more difficult and it is connected also to the capability of the nesting and nested model to reproduce the dynamics contained in the observations.