A MODEL COMPARISON - NUMERICAL SIMULATIONS OF THE NORTH AND EQUATORIAL ATLANTIC OCEANIC CIRCULATION IN-DEPTH AND ISOPYCNIC COORDINATES

A series of medium-resolution (similar to 1 degrees) numerical simulat ions for the equatorial and North Atlantic basin have been performed w ith two primitive equation models, one employing depth and the other d ensity as the vertical coordinate. The models have been configured for this exercise in as similar a fashion as their basic formulations all ow, and with fundamentally identical initialization, boundary conditio ns, and forcing functions for each of the experiments. The purpose of comparing the models' results is twofold: 1) to understand the degree to which model-generated circulation fields depend on the particular m odel architecture by examining the rate of divergence of the solutions of an isopycnic and a depth coordinate model given the same initial c onditions and 2) to uncover and remedy possible defects in either mode l design. The comparison is focused on the importance in each simulati on of the choice of mixing parameterization, which has a crucial impac t on the meridional overturning circulation, on the associated northwa rd heat transport, and on the evolution of water masses. Although the model-generated horizontal fields viewed at specific times during the integrations do not appear to be strongly dependent on the design of e ach model and are in good agreement with one another, the integrated p roperties of the depth coordinate model and the isopycnic coordinate m odel diverge significantly over time, with the depth coordinate model being unable to retain its most dense water masses after long integrat ion periods.