Please use this identifier to cite or link to this item: http://hdl.handle.net/10553/71072
Title: Seasonal variation of the South Indian tropical gyre
Authors: Aguiar González, Miguel Borja 
Ponsoni, Leandro
Ridderinkhof, Herman
van Aken, Hendrik M.
de Ruijter, Will P.M.
Maas, Leo R.M.
UNESCO Clasification: 251007 Oceanografía física
Keywords: South Indian Ocean tropical gyre
Seychelles–Chagos Thermocline Ridge
Seychelles Dome
Chagos Dome
Indonesian Throughflow Front
South Equatorial Countercurrent
Issue Date: 2016
Journal: Deep-Sea Research Part I: Oceanographic Research Papers 
Abstract: Based on satellite altimeter data and global atlases of temperature, salinity, wind stress and wind-driven circulation we investigate the seasonal variation of the South Indian tropical gyre and its associated open-ocean upwelling system, known as the Seychelles-Chagos Thermocline Ridge (SCTR). Results show a year-round, altimeter-derived cyclonic gyre where the upwelling regime appears closely related to seasonality of the ocean gyre, a relationship that has not been previously explored in this region. An analysis of major forcing mechanisms suggests that the thermocline ridge results from the constructive interaction of basin-scale wind stress curl, local-scale wind stress forcing and remote forcing driven by Rossby waves of different periodicity: semiannual in the west, under the strong influence of monsoonal winds; and, annual in the east, where the southeasterlies prevail. One exception occurs during winter, when the well-known westward intensification of the upwelling core, the Seychelles Dome, is shown to be largely a response of the wind-driven circulation. At basin-scale, the most outstanding feature is the seasonal shrinkage of the ocean gyre and the SCTR. From late autumn to spring, the eastward South Equatorial Countercurrent (SECC) recirculates early in the east on feeding the westward South Equatorial Current, therefore closing the gyre before arrival to Sumatra. We find this recirculation longitude migrates over 20° and collocates with the westward advance of a zonal thermohaline front emerging from the encounter between (upwelled) Indian Equatorial Water and relatively warmer and fresher Indonesian Throughflow Water. We suggest this front, which we call the Indonesian Throughflow Front, plays an important role as remote forcing to the tropical gyre, generating southward geostrophic flows that contribute to the early recirculation of the SECC.
URI: http://hdl.handle.net/10553/71072
ISSN: 0967-0637
DOI: 10.1016/j.dsr.2016.02.004
Source: Deep-Sea Research Part I [ISSN 0967-0637], v. 110, p.123-140
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