Response of the surface tropical Atlantic Ocean to wind forcing

Author(s)

Castellanos, Paola ^[1] ; Pelegri, Josep L. ^[2] ; Campos, Edmo J. D. ^[1] ; Rosell-Fieschi, Miquel ^[2] ; Gasser, Marc ^[2]

Affiliation

^[1] Univ Sao Paulo, Inst Oceanog, BR-05508 Sao Paulo - Brazil

^[2] CSIC, Inst Ciencias Mar, Dept Oceanog Fis & Tecnol, Barcelona - Spain

• Document type: Review article
• Source: PROGRESS IN OCEANOGRAPHY; v. 134, p. 271-292, MAY 2015.
• Web of Science Citations: 2

Abstract

We use 10 years of satellite data (sea level pressure, surface winds and absolute dynamic topography {[}ADT]) together with Argo-inferred monthly-mean values of near-surface velocity and water transport, to examine how the tropical system of near-surface zonal currents responds to wind forcing. The data is analyzed using complex Hilbert empirical orthogonal functions, confirming that most of the variance has annual periodicity, with maximum amplitudes in the region spanned by the seasonal displacement of the Inter-Tropical Convergence Zone (ITCZ). The ADT mirrors the shape of the upper isopycnals, hence becoming a good indicator of the amount of water stored in the upper ocean. Within about 3 from the Equator, where the Coriolis force is small, there is year-long meridional Ekman-transport divergence that would lead to the eastward transport of the Equatorial Undercurrent and its northern and southern branches. Beyond 3 of latitude, and at least as far as 20, the convergence of the Ekman transport generally causes a poleward positive ADT gradient, which sustains the westward South Equatorial Current (SEC). The sole exception occurs in summer, between 8 degrees N and 12 degrees N, when an Ekman-transport divergence develops and depletes de amount of surface water, resulting in an ADT ridge-valley system which reverses the ADT gradient and drives the eastward North Equatorial Countercurrent (NECC) at latitudes 4-9 N; in late fall, divergence ceases and the NECC drains the ADT ridge, so the ADT gradient again becomes positive and the SEC reappears. The seasonal evolution of a tilted ITCZ controls the surface water fluxes: the wind-induced transports set the surface divergence-convergence, which then drive the ADT and, through the ADT gradients, create the geostrophic jets that close the water balance. (C) 2015 Elsevier Ltd. All rights reserved. (AU)

• FAPESP's process: 13/08572-3 - Oceanic inter-hemispheric exchanges: Tropic-Extratropic Conecctions in the South Atlantic - analyses of observations and numerical results
• Grantee: Paola Maria Castellano Ossa Fernandes
• Support type: Scholarships in Brazil - Post-Doctorate
• FAPESP's process: 11/50552-4 - Impact of the Southern Atlantic on the global overturning circulation (MOC) and climate (SAMOC)
• Grantee: Edmo José Dias Campos
• Support type: Research Program on Global Climate Change - Thematic Grants
• FAPESP's process: 08/58101-9 - Impact of the Southwestern Atlantic Ocean on South American climate for the 20th and 21st centuries
• Grantee: Tercio Ambrizzi
• Support type: Research Program on Global Climate Change - Thematic Grants
• FAPESP's process: 10/01943-8 - Impacts of changes in the agulhas leakage on the South Atlantic (CALSA)
• Grantee: Edmo José Dias Campos
• Support type: Regular Research Grants