The development of a new ocean circulation model in the sigma coordinate system and its application to the western North Atlantic Ocean

A primitive equation model in the σ-coordinates system was formulated to remove the limitations of σ-coordinate model calculations over steep bottom topography. The model primitive equations are solved numerically using finite difference methods. Several experiments in a numerical basin having steep seamount topography are conducted to examine the differences between a conventional σ-coordinate model and the new model termed the Florida Tech Ocean Model (FOM). The new model is applied with full bottom topography to the limited regional area of the North Atlantic Ocean including the Florida Current, the Gulf Stream, and the Gulf Stream extension area.; Over steep bottom topography the FOM is found to be more numerically stable compared with conventional model formulations. During the model simulations prognostic variables such as temperature and velocity attained a quasi-steady state. In contrast, simulations with a conventional model formulation produced transient results and in some test cases, calculations over steep topography did not converge to numerical stability. These differences are attributed to the formulation of the governing equations rather than to numerical solution schemes.; The newly implemented model realistically simulates complicated ocean features in the limited regional area of the western North Atlantic Ocean. The major surface features such as the western boundary of the Florida Current and the Slope Water, the Gulf Stream, and the recirculatory current system are simulated without numerical instability over long-term integrations. The Deep Western Boundary Current (DWBC) along the continental rise is also simulated with little seasonal change. Predicted seasonal variability of surface temperature and volume transports of Gulf Stream System were comparable to published estimates based on observational data.