The three-dimensional primitive equation model, HAMSOM (HAMburg Shelf Ocean Model), was developed by Backhaus (1985) for the North Sea (Backhaus and Hainbucher, 1986). The model is based upon a semi-implicit numerical scheme described by Stronach et al. (1993). However, for the barotropic mode the model is implicit so that relatively large computational time steps can be employed. The HAMSOM model has been widely adapted to German Bight; Juan de Fuca system (Backhaus et al., 1987; Stronach et al., 1993); the South China Sea (Pohlmann, 1986), Atlantic coast off Spain and Baja California; and South-Western Australia (Pattiaratchi et al., 1996).
The model uses fixed permeable horizontal interfaces between layers and the equations of continuity and momentum are vertically integrated over each model layer. The distribution of pressure is assumed to be hydrostatic and the Boussinesq approximation is invoked. The model uses a finite difference scheme with the variables distributed over the grid according to the Arakawa C grid (Arakawa and Lamb, 1977). The solution technique is described in Backhaus (1985) and Stronach et al. (1993).
The HAMSOM model includes the choice of either one of three independent turbulent closure schemes for the computation of the vertical eddy viscosity (kz). These three schemes are based on the Richardson principle (Stronach et al., 1993), the Kochergin closure scheme (Kochergin, 1987) and constant kz in the water column. The horizontal eddy viscosity (kx) is considered constant everywhere. At the surface and bottom, boundary conditions are applied which include surface wind stress and bottom shear stress. The former is specified using a drag relationship dependent on the wind speed and direction. The bottom boundary condition is of the fprm of the quadratic bottom stress. At lateral solid boundaries, the usual no-flux condition is used while the roughness of a solid boundary can be considered by choosing no-slip, half-slip or full-slip boundary conditions. The sea surface elevation or the flow must be prescribed at open boundaries, or cyclic boundary conditions can be implemented.