Document Details
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Document Type |
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Thesis |
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Document Title |
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MIXED LAYER DEPTH VARIABILITY IN THE RED SEA AND THE GULF OF ADEN التغيرات في عمق طبقة الخلط في البحر الاحمر وخليج عدن |
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Subject |
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Faculty of Marine Sciences |
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Document Language |
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Arabic |
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Abstract |
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Oceanic mixed layer has potential influence on heat, freshwater exchange between atmosphere and ocean. The momentum energy, caused by drag of the surface on wind, is also transferred to the ocean through this layer. It has strong impact on the distribution of heat, ocean biology and near surface acoustic propagation. The conventional methods of MLD estimation are evaluated using the temperature and salinity profiles. Firstly, we examined threshold and gradient methods for estimating the MLD. Close evaluation with individual profiles reveals the failure of both methods for most of the profiles. Furthermore, the curvature method, a relatively recent approach to define ocean MLDs, is established for open water profiles but for marginal seas, like the Gulf of Aden, it detects shallower depths than the actual MLD.
The considerable differences motivated us to introduce a new approach of MLD identification, which is developed based on curvature method and is called segment method. Our segment method produces adequate MLD estimates for more than 95% of the profiles and overcomes major limitations of conventional methods. It is less biased and least scattered compared to other methods with a correlation coefficient > 0.95. The segment method is used to study the MLD variability in both the Red Sea and the Gulf of Aden and produced MLD climatology for the first time based on temperature profiles.
Northern end of the Red Sea experienced deeper mixing and higher MLD, associated with the winter cooling of the high-saline surface waters. Further, the region north of 19°N experienced deep mixed layers, irrespective of the season. Wind stress plays a major role in the MLD variability of the southern Red Sea, while net heat flux and evaporation are the dominating factors in the central and northern Red Sea regions. Ocean eddies and Tokar gap winds significantly alters the MLD structure in the Red Sea. The dynamics associated with the Tokar gap winds leads to a difference of more than 20 m in the average MLD between the north and south of the Tokar axis.
Similar to the Red Sea, the Gulf of Aden also shows strong spatial and temporal variability in the MLD structure. The western part of Gulf is generally deeper than central and eastern regions. In contradiction to the general pattern, the permanent anticyclonic eddy during summer in the central Gulf makes the region deeper than both eastern and western basin. Cyclonic and anticyclonic eddies are existed in other seasons also, but most of those eddies moves in the westward direction. Due to this effect, the localized signature of eddies is not visible in the climatological mixed layer. The signature of the wind induced upwelling along the southern coast during winter is clearly visible in the MLD structure. MLD of the Gulf of Aden is dominantly influenced by wind and eddies. The heat and freshwater exchange between ocean and atmosphere are significant, but their role in spatial and temporal variability of MLD are not clearly visible, indicating that these signals are weaker than that of wind and eddies. |
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Supervisor |
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Prof. Alaa Al-Barakati |
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Thesis Type |
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Doctorate Thesis |
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Publishing Year |
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1440 AH
2018 AD |
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Added Date |
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Sunday, December 16, 2018 |
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Researchers
| عبدالله شريري بويل | Poyil, Abdulla Cheriyeri | Researcher | Doctorate | |
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