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The influence of the land-sea breeze on coastal upwelling systems
The land-sea breeze is resonant with the inertial response of the ocean at the critical latitude of 30° N/S, however its role in the physical and biogeochemical functioning of eastern boundary upwelling systems (EBUS) is often over-looked. Here, we present a series of 1D, 2D, and 3D numerical experi...
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| Format: | Thesis |
| Language: | English |
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Department of Oceanography
2022
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| _version_ | 1867613155499180032 |
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| access_status_str | Open Access |
| author | Fearon, Giles |
| author2 | Vichi, Marcello |
| author_browse | Fearon, Giles Vichi, Marcello |
| author_facet | Vichi, Marcello Fearon, Giles |
| author_sort | Fearon, Giles |
| collection | Thesis |
| description | The land-sea breeze is resonant with the inertial response of the ocean at the critical latitude of 30° N/S, however its role in the physical and biogeochemical functioning of eastern boundary upwelling systems (EBUS) is often over-looked. Here, we present a series of 1D, 2D, and 3D numerical experiments which elucidate the drivers of diurnal-inertial variability and vertical mixing in EBUS due to land-sea breeze forcing near the critical latitude. The amplitude of the diurnal anticyclonic rotary component of the wind stress (τ ac0 ) is shown to be a good predictor of the locally forced response. The water depth plays an important role, where for shallow water depths (<∼100 m) surface oscillations are dampened and shear-driven mixing at the thermocline is reduced. Convergence/ divergence of the forced surface oscillations drive evanescent internal waves which elevate local vertical mixing above that from the forced response alone. The internal wave response is dampened by a gradually sloping bottom topography. St Helena Bay (∼32.5° S), in the southern Benguela upwelling system, possesses a combination of physical characteristics which favour an enhanced response to the land-sea breeze, namely a near-critical latitude, a local enhancement of τ ac0 , and a tendency for the development of a shallow stratified surface layer. Here, land-sea breeze forcing contributes to large diurnal variability in sea surface temperatures (SST's). During relaxation events, mean SST's are notably reduced due to land-sea breeze-driven vertical mixing. During upwelling events, the land-sea breeze drives a net warming of inner shelf waters primarily due to enhanced retention of the deepened surface mixed layer. The deepened thermocline impacts geostrophically-driven alongshore currents within St Helena Bay, which are strengthened (weakened) during upwelling (relaxation) events. It appears likely that the land-sea breeze plays an important role in the productivity of the system. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/35480 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:31:38.662Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2022 |
| publishDateRange | 2022 |
| publishDateSort | 2022 |
| 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:11427/35480 The influence of the land-sea breeze on coastal upwelling systems Fearon, Giles Vichi, Marcello Herbette, Steven Veitch, Jennifer Oceanography The land-sea breeze is resonant with the inertial response of the ocean at the critical latitude of 30° N/S, however its role in the physical and biogeochemical functioning of eastern boundary upwelling systems (EBUS) is often over-looked. Here, we present a series of 1D, 2D, and 3D numerical experiments which elucidate the drivers of diurnal-inertial variability and vertical mixing in EBUS due to land-sea breeze forcing near the critical latitude. The amplitude of the diurnal anticyclonic rotary component of the wind stress (τ ac0 ) is shown to be a good predictor of the locally forced response. The water depth plays an important role, where for shallow water depths (<∼100 m) surface oscillations are dampened and shear-driven mixing at the thermocline is reduced. Convergence/ divergence of the forced surface oscillations drive evanescent internal waves which elevate local vertical mixing above that from the forced response alone. The internal wave response is dampened by a gradually sloping bottom topography. St Helena Bay (∼32.5° S), in the southern Benguela upwelling system, possesses a combination of physical characteristics which favour an enhanced response to the land-sea breeze, namely a near-critical latitude, a local enhancement of τ ac0 , and a tendency for the development of a shallow stratified surface layer. Here, land-sea breeze forcing contributes to large diurnal variability in sea surface temperatures (SST's). During relaxation events, mean SST's are notably reduced due to land-sea breeze-driven vertical mixing. During upwelling events, the land-sea breeze drives a net warming of inner shelf waters primarily due to enhanced retention of the deepened surface mixed layer. The deepened thermocline impacts geostrophically-driven alongshore currents within St Helena Bay, which are strengthened (weakened) during upwelling (relaxation) events. It appears likely that the land-sea breeze plays an important role in the productivity of the system. 2022-01-14T12:23:00Z 2022-01-14T12:23:00Z 2021 2022-01-13T09:08:52Z Doctoral Thesis Doctoral PhD http://hdl.handle.net/11427/35480 eng application/pdf Department of Oceanography Faculty of Science |
| spellingShingle | Oceanography Fearon, Giles The influence of the land-sea breeze on coastal upwelling systems |
| thesis_degree_str | Doctoral |
| title | The influence of the land-sea breeze on coastal upwelling systems |
| title_full | The influence of the land-sea breeze on coastal upwelling systems |
| title_fullStr | The influence of the land-sea breeze on coastal upwelling systems |
| title_full_unstemmed | The influence of the land-sea breeze on coastal upwelling systems |
| title_short | The influence of the land-sea breeze on coastal upwelling systems |
| title_sort | influence of the land sea breeze on coastal upwelling systems |
| topic | Oceanography |
| url | http://hdl.handle.net/11427/35480 |
| work_keys_str_mv | AT fearongiles theinfluenceofthelandseabreezeoncoastalupwellingsystems AT fearongiles influenceofthelandseabreezeoncoastalupwellingsystems |