A barotropic global ocean model and its parallel implementation on unstructured grids

Unstructured grids can represent the complex geometry of the ocean basin with high fidelity. The lack of development tools supporting irregular grid problems discourages the use of such grids on parallel architectures. The state of the art ocean models are based on logically rectangular grids which makes it difficult to fit the complex ocean boundaries. In this paper, we demonstrate the use of unstructured triangular grids for solving a barotropic ocean model in spherical geometry with realistic continental boundaries. The model is based on the shallow water equations with a Coriolis force. A realistic wind forcing and a simple bottom friction term are also included. The numerical method is a cell based upwind finite volume scheme with explicit time stepping. From a parallelization point of view, that means there is only a nearest neighbour communication. A heuristic domain partitioning method was employed to distribute the load among processors. The resulting decomposition resembles 2D grid topology with some long distance communication paths. The model was implemented using the PVM message passing library and tested on a cluster of workstations and on an IBM SP2.