The purpose of this study is to test the feasibility of converting an atmosphere model code into an ocean model code, hence producing a single code that is valid for both atmosphere and ocean modelling. There are several motivations for doing this. Recent developments on numerical methods in the atmospheric sciences have permitted the elimination of some approximations that are traditionally applied to the primitive equations (hydrostatic approximation; filtering sound waves). The system of equations used in oceanographic models is a subset of the equations used in atmospheric model codes. The resources available to the Canadian atmospheric and oceanographic scientific community are limited, so sharing the same dynamical core would optimize its development and improvement. There will be increasing use of coupled atmosphere-ocean systems, which could be simplified by using the same code for both fluids. If this preliminary project is successful, a more general project would be conducted using a model with tangent linear and adjoint code for advanced data assimilation, thus facilitating future atmosphere-ocean data assimilation research and development.

Here a semi-implicit, semi-lagrangian algorithm developed for air flows has been adapted for the water. A unified nonhydrostatic equations system is used for both fluids. The dynamical kernel (advection and solver) is shared by both applications. Two types of vertical coordinate are available: height (with solid objects) and terrain following. The unified system of equations will be outlined. A series of theoretical (air and water) simulations was performed to test and validate the model. First comparisons and evaluations using the complete three-dimensional model in a coastal region will be presented.