الفهرس 
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Abstract
Monthly horizontal distributions of water temperature
4.3.1 Introduction
As previously mentioned, the climate of the Red Sea proper and its partial extension to the north in the Gulf of Suez is different to a certain extent from that of the Mediterranean. Such feature reveals that the water temperature in the northernmost of the Red Sea Proper and in the southern part of the Gulf is warmer than the water temperature in the northern part of the Gulf particularly in the winter season. The water temperature in the Red Sea as a whole is warm over the year round. Its deep water remains mostly constant between 21.5°C and 22.0°C against the deep water temperature everywhere in the world oceans. Such character is related to the existence of a shallow sill of about 140 m depth to the north of Bab-al-Mandab Strait that limited to a great extent the direct exchange of the deep water between the Red Sea and the Gulf of Aden. Accordingly, the heat storage within the Red Sea remains always high over the year round (El-Nikhely et al., 2010).
The temperature fields in the Red Sea proper suggest that north of 22°N latitude there may be northward flow against the wind in all months along the Arabian Coast, with wind-driven southward flow along the African Coast in all months, and with cross-sea flow in large eddies during the winter, December to May (Luksch, 1901). Bibik (1966) and Boisvert (1966) indicate the existence of a large cyclonic eddy in the northern Red Sea in winter.
In winter, the water temperature in a column of 200 m depth in the northernmost of the Red Sea Proper is found to be nearly homogeneous of about 22°C, as observed by many investigators due to the strong convection processes caused by the severe wind system dominated during that time of the year; while air temperature fluctuates between 6.0°C and 15.0°C only.
Hence, the water temperature in the upper surface layer that extends between the surface and 75 m depth shows values higher than 20.0°C in the offshore regions. Meanwhile, in the shallow areas and near shore regions, the water temperature is strongly influenced by the overlay air temperature as a result of the air-sea interaction through vertical convection processes.
In winter (December), the water temperature increases from 20°C at the head of the Gulf in the north to 24°C at the entrance in the south. Meanwhile in summer, the temperature is oscillating around 26°C from the north to the south of the Gulf. Moreover, an eastward increase of temperature was observed across the Gulf in winter (Luksch, 1901; Mohamed, 1940; and Morcos, 1970).
4.3.2 Results and discussions
The distribution of temperature, salinity and consequently density, at the surface and the other levels down to 50 m depth, reflects the seasonal cycle of summer heating and winter cooling (Patzert, 1972).
from January to March, the water in the upper surface layer (from the surface down to 200 m depth) at the northwesternmost of the Red Sea proper is mostly homothermal. The homogeneity of water in this region, due to cooling and the convergence of the surface water there, suggest a mechanism for the formation of the intermediate water. If the surface water in further cooled and mixed with the outflowing cold, highly saline bottom water from the Gulf of Suez may together contribute in the formation of the Red Sea deep water (Figures 4.1.a - 4.1.f).
The surface water temperature is mostly uniform in the offshore and deep water areas with temperature of 22.5°C - 23.0°C, while it shows slightly decrease at the entrance of the Suez
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and Aqaba Gulfs (22.0°C - 22.5°C ) due to the shallowness of these regions and to the influence of the overlay cold air.
In January, the water temperature at surface is about 22.5°C at the entrance of the Gulf of Suez (Hassan, 2010).
Such features differ from that observed at 10 m depth (Figure 4.1.b) due to the flowing of the Red Sea warm surface water (22.5°C- 23.0°C) into the Gulf along its both sides, against the prevailing wind from the north-northwest direction, as a result of the inclination of the mean sea level to the north due to the influence of the northeast monsoon on the Indian Ocean and the Arabian Sea in the south during that time of the year. Alasdair and Head (1987) noted that the northern part of the Red Sea proper is affected by the northwest to north winds.
In addition, one could notice the existence of less warm surface water at the Gulf entrance in the south as a tongue along the main navigation channel. This feature may be followed from the fact that the rate of the inflowing water into the Gulf at the surface may be higher than the rate of the outflowing water near the bottom plus that lost due to evaporation at surface. In this case, the Red Sea warm water at the entrance incorporates these water tongues or swallow them and reducing its temperature. Due to the existence of the islands mainly to the west of the navigation channel and the Gulf entrance in the south, the water flux becomes stronger and advances to the north more rapidly, than that moving to the east of the channel, and hence deflected to the right under the action of the earth rotational force “Coriolis Force”. Such behavior permits the less warm water in the Gulf to flow southward under the action of the northwest wind dominated at that time of the year. Such behavior will produce small scale rotational motion in this region. Accordingly, the water temperature near the eastern side will be lower than the temperature near the western side in this region between lat. 27.7°Nand 28.0 °N. At the same time, such procedure will need more time for the water parcels in this area to lose more water through evaporation processes, becomes cooler, more saline and hence denser and sink down to the bottom inside the Gulf. This water is then directed either to the south to flow out from the Gulf or to the north to complete its cycle, which is in agreement with the results reached by Soliman (1995).
Mohamed (1938) found that the surface temperature in the Gulf increases rapidly from north to south, while the variation of temperature with depth shows different patterns from one station to another taken over a short period of time - a phenomenon which illustrates the complex nature of the temperature regime in the Gulf.
Within the region extends from Ras Shukier to Ras Gharib the surface water temperature on the western side (" ~ " 20.0°C) is found to be less by one degree than that on the eastern side (" ~ "21.0°C). The same trend is also observed in the lower layers at 10 m, 20 m and 30 m depth respectively. This pattern could be explained either due to the upwelling of the cool bottom water (< 19°C) that may be taking place on the western side and the sinking of the warm surface water on the eastern side by the action of the forced west winds (" ~ "16 m/s) prevailing during that time of the year (Figure 3.11.b), or to the action of the rotational motions observed from time to time in the region.
Therefore, one may conclude that in addition to the horizontal rotational motion experienced in the Gulf, vertical rotational movements may also occur along and across the Gulf.
The distribution of water temperature at the layer of 20 m depth (Figure 4.1.c) also manifests the existence of rotational motion at lat. 28.5 °N. This motion results in sinking the water that cools at surface and hence cooling the whole water column. At latitude28.33°Na ridge appears across the Gulf leaving a narrow and shallow channel of about 50 m in depth and 9.5 km in width near the eastern side and a deep and relatively wider channel of more
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than 65 m in depth and 17.2 km in width which represent the main navigation route. This ridge is known as the Tor Bank which is covered by a water column of about 20 m from the surface. The existence of such bank in this area causes significant changes in the water structure and results in the appearance of many rotational motions and small scale eddies in front as well as behind the ridge.
At lat. 28.5 °N, the Gulf starts to increase in width up to 29.2°Nwhich could be considered as a small basin, showing the maximum width in the Gulf of about 52 km at lat. 28.9 oN. The capacity of this basin is about 110 * 109 m3, which represents " ~ " 37% of the whole Gulf. For that reason, the basin could be considered as a reservoir that receives water at a certain time from both directions, from the north, i.e. from the northernmost of the Gulf as well as from the south, i.e. from the southern part of the Gulf. Accordingly, the presence of a basin like that in the Gulf will play certainly an important role in the water circulation in the Gulf.
The wideness of the Gulf in that region will greatly reduce the current speed in the basin (1 - 2 cm/s), which agrees with the current observations recorded in the region (Figure 4.41). It also results in the followings:
i - Increasing its salinity due to the increase in the amount of less saline water loses at surface by evaporation,
ii - Through the air-sea interaction processes, the water in the basin will show rapid changes, either to become cooler or warmer according to the conditions of the overlying media.
iii - The water movements will be continuously developed according to the generating forces. Small scale eddy may be observed from time to time as that described by (Otterman, 1974).
iv - Upwelling may occur under the action of strong westerlies. This is evident in January and February particularly when strong west winds of speed greater than 15.0 m/s dominate (Figure 3.10.b). Evidently a positive temperature gradient is noticed across the Gulf with water temperature less than 17.0°C on the western side and more than 19.0°C on the eastern side. This feature is repeated at the lower layers till the bottom which has cooled further downward.
In fact, the occurrence of such water movements has significant impacts on the activities of the living organisms in the Gulf. The northernmost of the Gulf is cooled and the water there from January to March tends to be homogenous from the surface to the bottom. In winter, the cool season may extend from mid-October to mid-April with large scale prominent features (Abd-El-Rahman, 1993).
February may be considered as the lowest in water temperature in the Gulf and in the northernmost of the Red Sea proper and in particular in the areas existed directly to the south of the Gulf entrance in the circumstances of the islands (Figure 4.2.a – 4.2.f).
It is evident that the topographic features of the southern region to the Gulf have great influences on the horizontal distribution of its water temperature. In the offshore deep areas the water temperature is still warm of values higher than 22°C although the DROP in the air temperature that detected at Hurghada during that time of the year (max. temp. : 27.2°C, min. temp. : 9°C, and mean temp. : 17.6°C). In the shallow water areas, the temperature starts to decrease (21°C), while at the shelves, that extend for about one hundred km- the coastal areas and the regions near the islands and coral reefs, the temperature has reduced further to less than 20.0°C. This indicates that the offshore water is more or less stands at its relatively warm temperature due to the continuous convection processes, while the shallow areas loss much of
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their heat through the air-sea interaction processes. Accordingly, these regions could be considered as one of the places at which a large quantity of the Red Sea deep water is formed during winter season.
Moreover, due to the complicated topographic features at the entrance.