Numerical experiments with a three-dimensional model of an enclosed basin

A three-dimensional numerical model, for simulating velocity and temperature variations in a basin under various forcing mechanisms, is presented. Vertical structure is analyzed using a Galerkin Method with modified Chebyshev polynomials as expansion functions. With the proper choice of these functions, the barotropic and baroclinic parts of the motion are separated naturally in the model. A time-splitting procedure is then implemented; this makes time integration very efficient.Internal seiching due to windstress is simulated in the first experiment. Results are compared with those obtained using two-layered and 3D models. The geostrophic adjustment of a river flowing into a basin is then simulated. When friction and entrainment is neglected, flow adjusts to geostrophic balance over a distance about one third of the width of the basin. Weak turbulence has a large effect on the flow. For example, with a vertical eddy coefficient of 0.001 m² s⁻¹, isothermals are distorted so that their angle of intersection with the basin axis is large. Geostrophic adjustment still takes place over one third of the width but, due to frictional effects the flow is now quite large all over the lake.