Specification of Lateral Boundary Conditions in Three-Dimensional Mesoscale Numerical Models.

摘要

A difficult aspect of numerical modeling on the meso-beta scale is the specification of values on the lateral boundaries. This study uses a one-dimensional shallow water model with parameters appropriately specified for this scale to investigate a number of lateral boundary condition formulations. Two geostrophically imbalanced initial conditions are used to treat the boundary condition formulations. The scale of the disturbances was smaller than the Rossby radius of deformation and the adjustment process was completed rapidly by the redistribution of the height field by waves. The results of experiments with the model verified that any form of specified condition results in wave reflection at the boundary which destroys the physical solution. Extrapolation in the form of setting the gradient equal to zero was also shown to be inadequate. The sponge condition which is meant to absorb wave energy impinging on the boundary, provided acceptable solutions only if the specified boundary values were consistent with the geostrophically balanced interior. Several formulations of radiation condition were tested and the most accurate results were obtained when these were used. The radiation conditions did, however, allow a change of mass within the domain unless the phasespeeds of the outgoing waves were specified exactly.