SIMULATION OF THE ATLANTIC CIRCULATION WITH A COUPLED SEA ICE-MIXED LAYER-ISOPYCNIC GENERAL-CIRCULATION MODEL .2. MODEL EXPERIMENT

An ocean general circulation model (OGCM) formulated on isopycnal coor dinates is used to model the circulation of the Atlantic. The model do main is bounded meridionally at 30-degrees-S and the North Pole and ex tends zonally from 100-degrees-W to 50-degrees-E with cyclic boundary conditions in the Arctic basin. The Atlantic sector of the Arctic basi n is included in order to obtain a more realistic exchange of water ma sses between the North Atlantic and the Arctic. For the purpose of ach ieving a sufficient resolution of the high-latitude current systems, t he grid spacing is made variable with a 2-degrees x 2-degrees resoluti on in the entire equatorial and North Atlantic and a steadily increasi ng resolution in the Greenland-Iceland-Norwegian seas towards about 1- degrees zonally and 0.5-degrees meridionally. The model is integrated over 100 years, with acceleration of the deeper layers during the firs t 50 years. Initial conditions are observed annual mean temperature an d salinity. After the adjustment period the ocean approaches a cyclo-s tationary state, except for the deep ocean where temperature and salin ity have not become stationary. The model yields realistic equatorial currents and also simulates the separation of the Gulf Stream and the complex current structure in the Greenland-Iceland-Norwegian seas. Hea t and freshwater fluxes and the seasonal variation of the mixed-layer depth agree reasonably with observations. The stratification of the up per ocean demonstrates the capability of an isopycnal model with therm odynamics to reproduce the thermohaline circulation. Finally, the simu lated sea ice cover is considered in order to discuss the coupling amo ng sea ice, mixed layer, and the deep ocean.