A Study of Various open Boundary Conditions for Wind-Forced Barotropic Numerical Ocean Models

Abstract

Abstract This study focuses on the sensitivity of the interior wind-forced response of a numerical barotropic ocean model to changes in the open boundary conditions (OBCs) where the term “open” implies a sea boundary where the solution is unknown and must be assumed or extrapolated from the interior solution. Seven different OBCs are applied along the two Lateral boundaries of a rectangular basin with a flat bottom. One of the longer sides of the basin is a straight coast line, while the other is clamped (temporal derivative of the sea surface is set to zero). Each OBC is studied using three wind forcing schemes which test the the boundary under strong local forcing, under weak local forcing, and with a realistic wind field (moving cyclone). The different OBCs are compared with each other as well as with a “correct” case based on either an analytic solution (when available) or model results from an expanded model domain. Comparisons are shown in terms of sea level elevation, volume fluxes and excess mass. It is found that the interior response is often highly sensitive to the implemented OBC, that the performance of some OBCs is a strong function of the local wind forcing at the boundary, and that a method based on an integration along the characteristics performs well, and is generally superior to the others. The discussion also identifies the weaknesses and strengths of the OBCs.