The mass and heat budget in a model of the tropical Atlantic Ocean

Abstract

In a general circulation model of the tropical Atlantic Ocean, the northwestward flowing Brazilian Coastal Current is fed by the westward South Equatorial Countercurrent and in turn loses water to the eastward Equatorial Undercurrent and the eastward North Equatorial Countercurrent. The transport of the Countercurrent decreases in a downstream direction primarily because of downwelling and then equatorward flow, in the thermocline, into the undercurrent. Some of the Countercurrent water penetrates into the Gulf of Guinea, where it flows into the southern hemisphere. The transport of the Equatorial Undercurrent decreases because upwelling, which is most intense in the western side of the basin, transfers fluid into the surface layers to sustain divergent Ekman drift which is swept westward by the South Equatorial Undercurrent. The model has a northward heat transport across all latitudes in the tropics. Seasonal variations in this transport are modest to the south of 5°S and to the north of 15°N. Across 8°N, however, the transport varies from 1.5 × 1015 W in January and February to −0.1 × 1015 W in August. This result implies that the zonal bands 5°S to 8°N and 8°N to 15°N act as capacitors that are out of phase. In July, August, and September the heat gained from the southern hemisphere is stored in the 5°S to 8°N band where the thermocline deepens. During this period (when the Brazilian Coastal Current turns offshore near 5°N) the thermocline between 8°N and 15°N rises as heat is lost across 15°N. When the Brazilian Coastal Current flows continuously along the coast into the Gulf of Mexico, from December into May, it transports heat from the band 5°S to 8°N to replenish the heat stored between 8°N and 15°N and to sustain the heat flux across 15°N.