The buoyancy forcing of the Red Sea and its dynamical response are examined. Buoyancy transports through the Strait of Bab el Mandab, the major oceanic exchange point of the Red Sea with the open ocean, provide a strong constraint on the surface buoyancy fluxes. Hydrographic data and current records at the Strait require the annual mean surface heat flux to be −8 ± 2 W m⁻². For the annual mean freshwater fluxes the conservation of volume and salt give the net evaporation rate as 1.60 ± 0.35 m y⁻¹.
The surface fluxes estimated from the heat and freshwater transports at the Strait are compared to the annual mean surface fluxes estimated from standard meteorological data sets and formulae used on a global scale as in the revised Comprehensive Ocean-Atmosphere Data Set (UWM/COADS). The difference between the surface heat fluxes and that implied by the exchange through the Strait is large and close to 100 W m⁻². A large portion of this difference is explained by the overestimated solar irradiance due to the neglect of spatial and seasonal variations of aerosol concentration, and misapplication of a standard formula for insolation. Another portion of the difference comes from the underestimated longwave radiation due to the use of a bulk formula which is adequate for the open ocean but inappropriate for the Red Sea. The evaporative losses are also found to be underestimated, probably because of underestimated wind speeds. The net evaporation is the main contributor to the annual mean buoyancy loss approximately of 2 × 10⁻⁸ m² s⁻3.
The annual mean surface buoyancy flux, which is compatible with the oceanic buoyancy transport, is used with Phillips' similarity model to investigate the buoyancy driven flow of the upper 140m of the Red Sea. The observed stratification of the Red Sea can be achieved only with a very large eddy viscosity in the return flow. It is possible that this high vertical viscosity could be a proxy for processes neglected by this model such as bottom friction on the sloping boundaries. The effect of wind stress is small, but a southward wind combined with the bottom friction of a modified model with depth-dependent basin width could account for the viscous force required by a model.
The effectiveness of the bottom friction in retarding the flow depends on the magnitude of the lateral diffusion of momentum. To explore the possibility of measuring the horizontal momentum fluxes above a sloping boundary in a channel, we performed an experiment in the Strait of Georgia with two Acoustic Doppler Current Profilers. Although further investigation of such measurements is required and several issues remain to be resolved, it is shown that an estimate of the horizontal eddy viscosity acting on the tidal currents is possible with this method and gives about 50 m² s⁻¹ .
Overall, the dynamics of the Red Sea appears to be determined mainly by the surface buoyancy fluxes and internal and lateral frictional forces. Accurate modelling of the Red Sea requires improved knowledge of the forcing and of an appropriate parameterization of the friction. / Graduate
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/8801 |
| Date | 16 November 2017 |
| Creators | Tragou, Eleni-Anthi |
| Contributors | Garrett, Christopher J. R. |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | Available to the World Wide Web |
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