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 use s an Arakawa 'c' grid, give remarkably similar results. The new model avoids 'null space' problems of the standard 'a' grid approach by firs t using fourth-order interpolations to a 'c' grid advection velocity, then applying incompressibility to the result. Accuracy is further imp roved by using fourth-order pressure gradient approximations at 'a' gr id locations. Incompressibility with general geometry is satisfied eff iciently by a fast-converging iteration with a regular geometry ellipt ic solver. Results are compared with satellite-measured r.m.s. sea sur face elevation anomaly and detailed front structures, climatological m ean thermocline and empirical orthogonal functions and other observati ons.