Numerical ocean model study of the Agulhas Bank and the cool ridge

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dc.contributor.advisorShillington, Franken_ZA
dc.contributor.advisorPenven, Pierricken_ZA
dc.contributor.authorChang, Nicoletteen_ZA
dc.date.accessioned2015-02-10T13:42:41Z
dc.date.available2015-02-10T13:42:41Z
dc.date.issued2008en_ZA
dc.descriptionIncludes bibliographical references (p. [147]-158).en_ZA
dc.descriptionIncludes abstract.en_ZA
dc.description.abstractThe oceanic structure and circulation of the Agulhas Bank, the very wide continental shelf area off South Africa, has been explored in this thesis. The Agulhas Bank is a complex ocean region influenced by shelf processes as well as a nearby western boundary current, the Agulhas Current on its eastern margin and the Benguela Upwelling system on its western margin. In addition, a cold water feature, known as the cool ridge, has been observed on the Eastern Agulhas Bank. A consistent dynamical description is not available but it is commonly observed as a south-westerly flow of cold water in the upper water column, roughly following the 100m isobath and extending seawards off the coast. The formation of the cool ridge has also been investigated in this thesis by means of a numerical ocean model. Previous studies on the Agulhas Bank have been limited temporally and / or spatially. Thus, the Agulhas Bank as a whole has been inadequately sampled to provide a comprehensive representation. In order to remedy these deficiencies, the Regional Ocean Modeling System (ROMS) was used to study the Agulhas Bank dynamics. A large-scale model of the surrounding oceans, the SAfE (South African Experiment) configuration of the ROMS model, was used to force a one-way embedded finer-resolution model over the Agulhas Bank. This produced, 8 years of model data at an approximate horizontal resolution of 8km and 32 vertical terrain-following levels. Two main experiments were performed to understand the nature of the Agulhas Bank. Firstly, the "Reference Experiment" derived a seasonal ocean climatology of the Agulhas Bank. Secondly, the "No Agulhas Experiment" was carried out in an approach in which the Agulhas Current was removed from the shelf edge. A comparison of these two experiments yielded the influence of the Agulhas Current on the Agulhas Bank. The ROMS model was able to reproduce the main observed seasonal structure and circulation of the Agulhas Bank as well as the cool ridge. The Agulhas Bank showed marked seasonality, with its two-layer structure being significantly influenced by the Agulhas Current. The direct influence of the Agulhas Current on the Bank occurs on the Outer Agulhas Bank by the Agulhas Current itself or an Agulhas Current filament. Ekman veering by the interaction of the Agulhas Current with the bottom topography on the slope of the eastern Agulhas Bank advect cool water vertically onto the Bank. This strengthens the thermocline from below, in contrast to surface warming by solar insolation in summer and the Agulhas Current in winter. Cold waters, upwelled over the shelf edge, indirectly affect the greater Agulhas Bank by their advection by the predominantly westward mean currents. The most significant influence of the cold shelf-upwelled waters are in bringing cold waters to shallower depths over most of the Agulhas Bank. This may influence the waters that upwell at the coast, which on the eastern Agulhas Bank (without the Agulhas Current) are trapped under a thick warm surface layer.en_ZA
dc.identifier.apacitationChang, N. (2008). <i>Numerical ocean model study of the Agulhas Bank and the cool ridge</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Oceanography. Retrieved from http://hdl.handle.net/11427/12426en_ZA
dc.identifier.chicagocitationChang, Nicolette. <i>"Numerical ocean model study of the Agulhas Bank and the cool ridge."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Oceanography, 2008. http://hdl.handle.net/11427/12426en_ZA
dc.identifier.citationChang, N. 2008. Numerical ocean model study of the Agulhas Bank and the cool ridge. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Chang, Nicolette AB - The oceanic structure and circulation of the Agulhas Bank, the very wide continental shelf area off South Africa, has been explored in this thesis. The Agulhas Bank is a complex ocean region influenced by shelf processes as well as a nearby western boundary current, the Agulhas Current on its eastern margin and the Benguela Upwelling system on its western margin. In addition, a cold water feature, known as the cool ridge, has been observed on the Eastern Agulhas Bank. A consistent dynamical description is not available but it is commonly observed as a south-westerly flow of cold water in the upper water column, roughly following the 100m isobath and extending seawards off the coast. The formation of the cool ridge has also been investigated in this thesis by means of a numerical ocean model. Previous studies on the Agulhas Bank have been limited temporally and / or spatially. Thus, the Agulhas Bank as a whole has been inadequately sampled to provide a comprehensive representation. In order to remedy these deficiencies, the Regional Ocean Modeling System (ROMS) was used to study the Agulhas Bank dynamics. A large-scale model of the surrounding oceans, the SAfE (South African Experiment) configuration of the ROMS model, was used to force a one-way embedded finer-resolution model over the Agulhas Bank. This produced, 8 years of model data at an approximate horizontal resolution of 8km and 32 vertical terrain-following levels. Two main experiments were performed to understand the nature of the Agulhas Bank. Firstly, the "Reference Experiment" derived a seasonal ocean climatology of the Agulhas Bank. Secondly, the "No Agulhas Experiment" was carried out in an approach in which the Agulhas Current was removed from the shelf edge. A comparison of these two experiments yielded the influence of the Agulhas Current on the Agulhas Bank. The ROMS model was able to reproduce the main observed seasonal structure and circulation of the Agulhas Bank as well as the cool ridge. The Agulhas Bank showed marked seasonality, with its two-layer structure being significantly influenced by the Agulhas Current. The direct influence of the Agulhas Current on the Bank occurs on the Outer Agulhas Bank by the Agulhas Current itself or an Agulhas Current filament. Ekman veering by the interaction of the Agulhas Current with the bottom topography on the slope of the eastern Agulhas Bank advect cool water vertically onto the Bank. This strengthens the thermocline from below, in contrast to surface warming by solar insolation in summer and the Agulhas Current in winter. Cold waters, upwelled over the shelf edge, indirectly affect the greater Agulhas Bank by their advection by the predominantly westward mean currents. The most significant influence of the cold shelf-upwelled waters are in bringing cold waters to shallower depths over most of the Agulhas Bank. This may influence the waters that upwell at the coast, which on the eastern Agulhas Bank (without the Agulhas Current) are trapped under a thick warm surface layer. DA - 2008 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2008 T1 - Numerical ocean model study of the Agulhas Bank and the cool ridge TI - Numerical ocean model study of the Agulhas Bank and the cool ridge UR - http://hdl.handle.net/11427/12426 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/12426
dc.identifier.vancouvercitationChang N. Numerical ocean model study of the Agulhas Bank and the cool ridge. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Oceanography, 2008 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/12426en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Oceanographyen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherOceanographyen_ZA
dc.titleNumerical ocean model study of the Agulhas Bank and the cool ridgeen_ZA
dc.typeDoctoral Thesis
dc.type.qualificationlevelDoctoral
dc.type.qualificationnamePhDen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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