Seasonal Variability of Heat and Mass Transport Process in the Upper Tropical Atlantic Ocean: A Numerical Model Study

• Main Author: Lee, Sang-Ki
• Format: Text
• Language: unknown
• Published: ODU Digital Commons 1995
• Subjects: Heat transfer; Oceanography; Curl; North Atlantic
• Online Access: https://digitalcommons.odu.edu/oeas_etds/51; https://digitalcommons.odu.edu/cgi/viewcontent.cgi?article=1054&context=oeas_etds

A simple 2.5 layer numerical model was developed and used to illustrate the seasonal variability of heat and mass transports in the upper tropical Atlantic Ocean, associated with the seasonal movement of the Inter-Tropical Convergence Zone (ITCZ). The model ocean was forced by seasonally varying climatological wind and heat flux fields. The entrainment at the base of the mixed layer was scaled by wind stress and shear at the bottom of the mixed layer. On an annual average, the northward transport of the tropical warm water is about 11 Sv, with roughly 10 Sv associated with entrainment of upper thermocline water and the other 1 Sv executing a cross-equatorial path continuously from the South Atlantic. Out of the total 10 Sv of the needed upper thermocline water, 9 Sv enters the equatorial belt from the South Atlantic. The seasonal response to the ITCZ movement was most striking in the entrainment rate and the warm water escape rate across the northern edge of the equatorial cell. The entrainment rate was found to be significant during May/December and ceased between January and April. The locally forced equilibrium response between the interfacial shear and the zonal wind stress east of 30°W appears to be responsible for this cycle. The warm water escape toward the North Atlantic takes place mainly between December and May and stops during July/September. Further investigation suggested that the seasonal intensification of the North Equatorial Countercurrent (NECC) serves as a major obstacle to the warm water escape: during July/September the strong negative wind stress curl north of the equator intensifies the NECC, which requires a source of mass at its origin in the west. The North Brazil Current (NBC), therefore, veers offshore completely and provides the mass, terminating the warm water escape via the NBC-Guiana Current route. Strengthening of the NECC also steepens the mixed layer floor, forming a strong potential vorticity front along the northern edge of the NECC. The northward warm water escape via the ...