Modelling the mesoscale variability in the greater Agulhas Current system using hybrid coordinate Ocean model

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dc.contributor.advisorReason, Chrisen_ZA
dc.contributor.advisorJohannessen, y Johnny Aen_ZA
dc.contributor.advisorBertino, Laurenten_ZA
dc.contributor.authorBackeberg, Bjorn Christophen_ZA
dc.date.accessioned2014-08-13T19:48:11Z
dc.date.available2014-08-13T19:48:11Z
dc.date.issued2009en_ZA
dc.description.abstractThe ocean circulation dynamics in the greater Agulhas Current system are dominated by mesoscale variability, which is highly non-linear, and therefore difficult to measure and simulate accurately. Moreover, the shedding of Agulhas rings from the retroflection south of Africa, which is the dominant mechanism by which warm and saline water flows from the Indian into the Atlantic Ocean, is thought to be a crucial component of the thermohaline circulation. With the goal of providing an accurate simulation of the greater Agulhas Current system, and in particular its mesoscale variability, a high resolution Hybrid Coordinate Ocean Model is set up in a nested configuration. In two 11 year simulation experiments, the effect of a higher order momentum advection scheme on the simulated ocean dynamics is tested and evaluated against available satellite observations and in-situ measurements. Quantitative analyses and model validation methods are developed to objectively evaluate the simulation experiments. The resultant skewness analyses and spatial variograms are objective measures for assessing the model simulation and additionally provide new insights on the mesoscale dynamics of the greater Agulhas Current system. A 4th order momentum advection scheme is shown to significantly improve the simulation of the region, in particular the dynamics of the southern Agulhas Current and the retroflection are greatly improved. From the analyses of the two model simulations in conjunction with satellite observations and in-situ measurements, it is found that the Indo-Atlantic inter-ocean exchange, and the shedding of Agulhas rings from the retroflection, is sensitive to the strength of the Agulhas Current, which in turn is influenced by the flow dynamics in the Mozambique Channel and south of Madagascar. Mesoscale eddies drifting from these source regions to the Agulhas Current play an important role, and the connection between the Agulhas Current and the respective source regions provides a link to large-scale variability in the Indian Ocean, which in turn is related to interannual modes of variability such as the Indian Ocean Dipole and El NiÑo Southern Oscillation.en_ZA
dc.identifier.apacitationBackeberg, B. C. (2009). <i>Modelling the mesoscale variability in the greater Agulhas Current system using hybrid coordinate Ocean model</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Oceanography. Retrieved from http://hdl.handle.net/11427/6458en_ZA
dc.identifier.chicagocitationBackeberg, Bjorn Christoph. <i>"Modelling the mesoscale variability in the greater Agulhas Current system using hybrid coordinate Ocean model."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Oceanography, 2009. http://hdl.handle.net/11427/6458en_ZA
dc.identifier.citationBackeberg, B. 2009. Modelling the mesoscale variability in the greater Agulhas Current system using hybrid coordinate Ocean model. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Backeberg, Bjorn Christoph AB - The ocean circulation dynamics in the greater Agulhas Current system are dominated by mesoscale variability, which is highly non-linear, and therefore difficult to measure and simulate accurately. Moreover, the shedding of Agulhas rings from the retroflection south of Africa, which is the dominant mechanism by which warm and saline water flows from the Indian into the Atlantic Ocean, is thought to be a crucial component of the thermohaline circulation. With the goal of providing an accurate simulation of the greater Agulhas Current system, and in particular its mesoscale variability, a high resolution Hybrid Coordinate Ocean Model is set up in a nested configuration. In two 11 year simulation experiments, the effect of a higher order momentum advection scheme on the simulated ocean dynamics is tested and evaluated against available satellite observations and in-situ measurements. Quantitative analyses and model validation methods are developed to objectively evaluate the simulation experiments. The resultant skewness analyses and spatial variograms are objective measures for assessing the model simulation and additionally provide new insights on the mesoscale dynamics of the greater Agulhas Current system. A 4th order momentum advection scheme is shown to significantly improve the simulation of the region, in particular the dynamics of the southern Agulhas Current and the retroflection are greatly improved. From the analyses of the two model simulations in conjunction with satellite observations and in-situ measurements, it is found that the Indo-Atlantic inter-ocean exchange, and the shedding of Agulhas rings from the retroflection, is sensitive to the strength of the Agulhas Current, which in turn is influenced by the flow dynamics in the Mozambique Channel and south of Madagascar. Mesoscale eddies drifting from these source regions to the Agulhas Current play an important role, and the connection between the Agulhas Current and the respective source regions provides a link to large-scale variability in the Indian Ocean, which in turn is related to interannual modes of variability such as the Indian Ocean Dipole and El NiÑo Southern Oscillation. DA - 2009 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2009 T1 - Modelling the mesoscale variability in the greater Agulhas Current system using hybrid coordinate Ocean model TI - Modelling the mesoscale variability in the greater Agulhas Current system using hybrid coordinate Ocean model UR - http://hdl.handle.net/11427/6458 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/6458
dc.identifier.vancouvercitationBackeberg BC. Modelling the mesoscale variability in the greater Agulhas Current system using hybrid coordinate Ocean model. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Oceanography, 2009 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/6458en_ZA
dc.language.isoeng
dc.publisher.departmentDepartment of Oceanographyen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherOceanographyen_ZA
dc.titleModelling the mesoscale variability in the greater Agulhas Current system using hybrid coordinate Ocean modelen_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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