Seasonal Cycle of the Mixed Layer Heat Budget in the Northeastern Tropical Atlantic Ocean

• Published in: Journal of climate 2013-10, Vol.26 (20), p.8169-8188
• Main Authors: Foltz, Gregory R., Schmid, Claudia, Lumpkin, Rick
• Format: Article
• Language: English
• Subjects: Advection; Annual cycles; Annual variations; Barrier layers; Climate; Coasts; Convergence zones; Cooling; Earth, ocean, space; Enthalpy; Equator; Evaporative cooling; Exact sciences and technology; Experiments; External geophysics; Heat; Heat balance; Heat budget; Heat content; Heat flux; Heat storage; Heat transfer; Intertropical convergence zone; Meteorology; Mixed layer; Oceans; Physics of the oceans; Quality control; Radiation; Salinity; Seasonal variation; Seasonal variations; Short wave radiation; Studies; Summer; Thermohaline structure and circulation. Turbulence and diffusion; Trade winds; Turbulent mixing; Wind
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/jcli-d-13-00037.1

The seasonal cycle of the mixed layer heat budget in the northeastern tropical Atlantic (0°–25°N, 18°–28°W) is quantified using in situ and satellite measurements together with atmospheric reanalysis products. This region is characterized by pronounced latitudinal movements of the intertropical convergence zone (ITCZ) and strong meridional variations of the terms in the heat budget. Three distinct regimes within the northeastern tropical Atlantic are identified. The trade wind region (15°–25°N) experiences a strong annual cycle of mixed layer heat content that is driven by approximately out-of-phase annual cycles of surface shortwave radiation (SWR), which peaks in boreal summer, and evaporative cooling, which reaches a minimum in boreal summer. The surface heat-flux-induced changes in the mixed layer heat content are damped by a strong annual cycle of cooling from vertical turbulent mixing, estimated from the residual in the heat balance. In the ITCZ core region (3°–8°N) a weak seasonal cycle of mixed layer heat content is driven by a semiannual cycle of SWR and damped by evaporative cooling and vertical turbulent mixing. On the equator the seasonal cycle of mixed layer heat content is balanced by an annual cycle of SWR that reaches a maximum in October and a semiannual cycle of turbulent mixing that cools the mixed layer most strongly during May–July and November. These results emphasize the importance of the surface heat flux and vertical turbulent mixing for the seasonal cycle of mixed layer heat content in the northeastern tropical Atlantic.