OPEN BOUNDARY-CONDITIONS FOR A NUMERICAL SHELF SEA MODEL

The barotropic numerical shelf sea model of the Institute of Atmospher ic Physics, Chinese Academy of Sciences, is outlined first. For comput ing economy, a splitting method is applied by dividing the governing e quations into three stages which are integrated with different time-st eps. Open boundary conditions suitable for the different stages are de rived from the locally linearized versions of the split governing equa tions. For the adjustment stage, the governing equations are converted to an equivalent set of characteristic equations, which represent wav es propagating into or out of the computational domain. The outgoing w aves are described by characteristic equations, while the incoming wav es are suppressed by a nonreflecting boundary condition. For the devel opment stage, general analytical solutions are found. At outflow point s the boundary values at the upper time-level are obtained from data a t the present time-level within and on the boundary via the analytical solutions, while the boundary values at inflow points remain constant in time. For the forcing-dissipation stage no boundary conditions are necessary. Numerical verification of the proposed open boundary condi tions is described; the results are satisfactory. (C) 1995 Academic Pr ess, Inc.