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

摘要

The specification of lateral boundary conditions in meso-beta scale models is investigated with the use of a one dimensional shallow water model and a full three dimensional atmospheric model. A large number of boundary condition schemes and variations on these schemes are tested in the one dimensional model using initial conditions which are not in geostrophic balance to determine the ability of the boundary condition to allow geostrophic adjustment to proceed in the model. The radiation type boundary conditions tested are found to be superior to all other schemes, with the flow relaxation scheme also producing acceptable results. Initial conditions similar to those used in the one dimensional model are used to test the sponge, flow relaxation, one dimensional radiation and multi dimensional radiation conditions in the three dimensional model. While all conditions had certain strengths and weaknesses depending on the specific form of the initial condition, the one dimensional radiation condition gave the best overall results. The one-dimensional model was further used to investigate the geostrophic adjustment of the model to large scale imbalances and to test some methods of nesting the mesoscale model. It is found that while the pressure or height fields rapidly adjust to the winds for disturbances within the domain, the adjustment to imposed large scale gradients takes place in the wind field on the much slower time scale given by the inertial period.