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The role of short-term atmospheric variability in shaping Lagrangian transport in the Southern Benguela
This work studies the links between the Lagrangian transport in the Southern Benguela upwelling system and the ocean circulation through modelling experimentation. More specifically, it intends to show that the wind-induced circulation at short-time scales impacts the drift of Lagrangian particles r...
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| Format: | Thesis |
| Language: | English |
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Department of Oceanography
2016
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| _version_ | 1867613275894579200 |
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| access_status_str | Open Access |
| author | Ragoasha, Moagabo Natalie |
| author2 | Reason, Chris |
| author_browse | Ragoasha, Moagabo Natalie Reason, Chris |
| author_facet | Reason, Chris Ragoasha, Moagabo Natalie |
| author_sort | Ragoasha, Moagabo Natalie |
| collection | Thesis |
| description | This work studies the links between the Lagrangian transport in the Southern Benguela upwelling system and the ocean circulation through modelling experimentation. More specifically, it intends to show that the wind-induced circulation at short-time scales impacts the drift of Lagrangian particles released in the model. Three ocean model (ROMS) simulations are set-up. Simulation A is forced with a6 hourly atmospheric forcing (surface heat and fresh-water fluxes and wind stress). In simulation B and C, the atmospheric forcing is low-pass filtered with 5 days and 30 days cut-off periods. The ocean model outputs are averaged and saved at deferent temporal frequency: frequencies of 6 hours and 3 days. Particles released in the Lagrangian tracking tool are transported by the velocity vectors produced by the ocean model into the nursery area located at Saint Helena Bay. The presence of short-term fluctuations result in higher inner shelf transport and amore elongated plume dispersion pattern with much refine spatial scales. This finding contrasts with previous studies where the inner shelf transport success was always low compared to the outer shelf nursery. When the high frequency signal is filtered out, the inner shelf transport is greatly reduced especially during the upwelling season. The archiving frequency of the ROMS output is shown to impact Lagrangian studies, especially when the atmospheric forcing has variability at short time scales (less than 5 days).Monthly mean forcing results in dynamics variable with periods of not less than a month and 5 daily averaged forcing with sub-weekly dynamics. Therefore, in simulations B and C the less than 3 days archiving of the model outputs is not necessary, because their forcing does not generate dynamics with such periods. The latter must be adapted so that it does not filter out the ocean response to the high frequency atmospheric forcing. To explain the Lagrangian transports, as a first approach, the transport success was linked to the variability of the ocean circulation. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/20006 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:33:33.643Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2016 |
| publishDateRange | 2016 |
| publishDateSort | 2016 |
| publisher | Department of Oceanography |
| publisherStr | Department of Oceanography |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/20006 The role of short-term atmospheric variability in shaping Lagrangian transport in the Southern Benguela Ragoasha, Moagabo Natalie Reason, Chris Ocean and Climate Science This work studies the links between the Lagrangian transport in the Southern Benguela upwelling system and the ocean circulation through modelling experimentation. More specifically, it intends to show that the wind-induced circulation at short-time scales impacts the drift of Lagrangian particles released in the model. Three ocean model (ROMS) simulations are set-up. Simulation A is forced with a6 hourly atmospheric forcing (surface heat and fresh-water fluxes and wind stress). In simulation B and C, the atmospheric forcing is low-pass filtered with 5 days and 30 days cut-off periods. The ocean model outputs are averaged and saved at deferent temporal frequency: frequencies of 6 hours and 3 days. Particles released in the Lagrangian tracking tool are transported by the velocity vectors produced by the ocean model into the nursery area located at Saint Helena Bay. The presence of short-term fluctuations result in higher inner shelf transport and amore elongated plume dispersion pattern with much refine spatial scales. This finding contrasts with previous studies where the inner shelf transport success was always low compared to the outer shelf nursery. When the high frequency signal is filtered out, the inner shelf transport is greatly reduced especially during the upwelling season. The archiving frequency of the ROMS output is shown to impact Lagrangian studies, especially when the atmospheric forcing has variability at short time scales (less than 5 days).Monthly mean forcing results in dynamics variable with periods of not less than a month and 5 daily averaged forcing with sub-weekly dynamics. Therefore, in simulations B and C the less than 3 days archiving of the model outputs is not necessary, because their forcing does not generate dynamics with such periods. The latter must be adapted so that it does not filter out the ocean response to the high frequency atmospheric forcing. To explain the Lagrangian transports, as a first approach, the transport success was linked to the variability of the ocean circulation. 2016-06-10T07:40:27Z 2016-06-10T07:40:27Z 2015 Master Thesis Masters MSc http://hdl.handle.net/11427/20006 eng application/pdf Department of Oceanography Faculty of Science University of Cape Town |
| spellingShingle | Ocean and Climate Science Ragoasha, Moagabo Natalie The role of short-term atmospheric variability in shaping Lagrangian transport in the Southern Benguela |
| thesis_degree_str | Master's |
| title | The role of short-term atmospheric variability in shaping Lagrangian transport in the Southern Benguela |
| title_full | The role of short-term atmospheric variability in shaping Lagrangian transport in the Southern Benguela |
| title_fullStr | The role of short-term atmospheric variability in shaping Lagrangian transport in the Southern Benguela |
| title_full_unstemmed | The role of short-term atmospheric variability in shaping Lagrangian transport in the Southern Benguela |
| title_short | The role of short-term atmospheric variability in shaping Lagrangian transport in the Southern Benguela |
| title_sort | role of short term atmospheric variability in shaping lagrangian transport in the southern benguela |
| topic | Ocean and Climate Science |
| url | http://hdl.handle.net/11427/20006 |
| work_keys_str_mv | AT ragoashamoagabonatalie theroleofshorttermatmosphericvariabilityinshapinglagrangiantransportinthesouthernbenguela AT ragoashamoagabonatalie roleofshorttermatmosphericvariabilityinshapinglagrangiantransportinthesouthernbenguela |