A SEMIIMPLICIT OCEAN CIRCULATION MODEL USING A GENERALIZED TOPOGRAPHY-FOLLOWING COORDINATE SYSTEM

We introduce a new ocean circulation model featuring an improved vertical coordinate representation. This new coordinate is a generalized sigma-coordinate; however, it is capable of simultaneously maintaining high resolution in the surface layer as well as dealing with steep and/or tall topography. The model equations are the three-dimensional, free surface, primitive equatins with orthogonal curvilinear coordinates in the horizontal and the new general coordinate in the vertical. Vertical mixing is treated implicitly by the generalized Crank-Nicolson method based on a Galerkin finite element formulation. Two alternate parameterizations of surface mixing are incorporated, based respectively on the approaches of Price, Weller, and Pinkel and Mellor and Yamada. Finally, a quadrature formula of Lagrange interpolation is employed to produce a more accurate calculation of pressure and vertical velocity. Three tests are used to demonstrate the accuracy, stability, and applicability of the model: the diurnal cycling of the surface mixed layer, flow around a tall seamount, and a regional simulation of the California current system. (C) 1994 Academic Press, Inc.