In the last two decades several criteria have emerged by which oceanographers classify their models (see Figure 1). Geography is clearly one criterion, with models being designed for the world ocean, the Atlantic and Pacific Basins, the Mediterranean, the Gulf of Mexico, etc. A second criterion utilizes the physical processes described: models can be hydrodynamic, thermodynamic or both. The surface mixed layer models mentioned above fit into the thermodynamic class, and some of the simple layered models (see below) are of the hydrodynamic type. A third criterion is concerned with the condition one puts on the surface of the ocean. A fourth is concerned with the way the vertical degree of freedom is handled (including modal decomposition in the vertical), and a fifth with the presence of density variations.
Figure 1: Ocean Models.