A SEMI-COLLOCATED OCEAN MODEL-BASED ON THE SOMS APPROACH

In application to the Gulf of Mexico (GOM), a new DieCAST ocean model, which uses a modified Arakawa 'a' grid, and the SOMS model, which uses an Arakawa 'c' grid, give remarkably similar results. The new model avoids 'null space' problems of the standard 'a' grid approach by first using fourth-order interpolations to a 'c' grid advection velocity, then applying incompressibility to the result. Accuracy is further improved by using fourth-order pressure gradient approximations at 'a' grid locations. Incompressibility with general geometry is satisfied efficiently by a fast-converging iteration with a regular geometry elliptic solver. Results are compared with satellite-measured r.m.s. sea surface elevation anomaly and detailed front structures, climatological mean thermocline and empirical orthogonal functions and other observations.