The Development of a New Ocean Circulation Model in the Sigma
Coordinate System: Numerical Basin Tests and Application to the
Western North Atlantic Ocean
Gary A. Zarillo and Sang Sup Yuk
Division of Marine and Environmental System
Florida Institute of Technology, Melbourne. FL
A primitive equation model in the s-coordinates system was formulated
to remove the limitations of s-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 s-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.