The influence of the land-sea breeze on coastal upwelling systems

dc.contributor.advisorVichi, Marcello
dc.contributor.advisorHerbette, Steven
dc.contributor.advisorVeitch, Jennifer
dc.contributor.authorFearon, Giles
dc.date.accessioned2022-01-14T12:23:00Z
dc.date.available2022-01-14T12:23:00Z
dc.date.issued2021
dc.date.updated2022-01-13T09:08:52Z
dc.description.abstractThe 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.
dc.identifier.apacitationFearon, G. (2021). <i>The influence of the land-sea breeze on coastal upwelling systems</i>. (). ,Faculty of Science ,Department of Oceanography. Retrieved from http://hdl.handle.net/11427/35480en_ZA
dc.identifier.chicagocitationFearon, Giles. <i>"The influence of the land-sea breeze on coastal upwelling systems."</i> ., ,Faculty of Science ,Department of Oceanography, 2021. http://hdl.handle.net/11427/35480en_ZA
dc.identifier.citationFearon, G. 2021. The influence of the land-sea breeze on coastal upwelling systems. . ,Faculty of Science ,Department of Oceanography. http://hdl.handle.net/11427/35480en_ZA
dc.identifier.ris TY - Doctoral Thesis AU - Fearon, Giles AB - 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. DA - 2021_ DB - OpenUCT DP - University of Cape Town KW - Oceanography LK - https://open.uct.ac.za PY - 2021 T1 - The influence of the land-sea breeze on coastal upwelling systems TI - The influence of the land-sea breeze on coastal upwelling systems UR - http://hdl.handle.net/11427/35480 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/35480
dc.identifier.vancouvercitationFearon G. The influence of the land-sea breeze on coastal upwelling systems. []. ,Faculty of Science ,Department of Oceanography, 2021 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/35480en_ZA
dc.language.rfc3066eng
dc.publisher.departmentDepartment of Oceanography
dc.publisher.facultyFaculty of Science
dc.subjectOceanography
dc.titleThe influence of the land-sea breeze on coastal upwelling systems
dc.typeDoctoral Thesis
dc.type.qualificationlevelDoctoral
dc.type.qualificationlevelPhD
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