Open AccessDouble‐celled subtropical gyre in the South Atlantic Ocean: Means, trends, and interannual changes
Author(s) -
Vianna M. L.,
Menezes V. V.
Publication year - 2011
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2010jc006574
Subject(s) - ocean gyre , geology , oceanography , subtropics , climatology , altimeter , front (military) , sea surface height , current (fluid) , ocean current , boundary current , meander (mathematics) , sea level , sea surface temperature , geodesy , geometry , mathematics , fishery , biology
We present here a study of the mean upper layer structure of the South Atlantic Subtropical Gyre (SASG) and its modes of variability based on Archiving, Validation, and Interpretation of Satellite Oceanographic data sea level anomaly data, Gravity Recovery and Climate Experiment‐based mean dynamic topography (MDT) models, Reynolds sea surface temperatures, and two tide gauge time series from Permanent Service for Mean Sea Level. Analysis of the MDTs shows that the SASG mean structure is represented by a double‐cell circulation, the southern cell being a narrow quasi‐zonal strip centered around 33°S. Its southern limb is limited by the recently discovered Saint Helena Current/Tristan da Cunha Current (StHC/TCC) and the North Subtropical Front around 35°S. This system is shown to be well separated from the South Atlantic Current/South Subtropical Front around 42–45°S. A method based on singular spectrum analysis was used to determine the principal modes of variability through the decomposition of the data into band‐passed data sets. The altimeter sea level trend analysis suggests that the SASG pattern is slowly migrating southward and has been growing in amplitude between 1994 and 2006 with local growth rates of 5–10 mm/yr occurring in the southern cell. Flow intensifications in this period (2–3 cm/s in the South Equatorial Current and North Brazil Undercurrent, 3.5 cm/s in the Benguela Current), and weakening by 4.5 cm/s in the StHC/TCC are recorded. The altimeter‐derived sea level trend is coherent with the growing phase of a bidecadal oscillation found from both tide gauges.