strait of gibraltar

Pelayo García-Pardo Martín-SerranoDeck Cadet

I NDEX

CLIMATE OF THE STRAIT OF GIBRALTAR

Climate of the Strait of Gibraltar

1. WHAT IS THE STRAIT OF GIBRALTAR?...................3

2. LOCATION……………………………………………...4

Extension

3. GEOLOGY………………………………………...……5

4. FLOW AND WAVE PATTERNS……………………….6

Inflow and outflow Internal waves

5. THE ATLANTIC OCEAN……………………………….9

Characteristics Water Climate

6. THE MEDITERRANIAN SEA…………………………11

Oceanography Strait of Gibraltar sea temperature (Cº) Atlantic sea temp VS Mediterranean sea

temp

7. WINDS IN THE STRAIT OF GIBRALTAR…………...13

Levant The Gibraltar levanter cloud

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8. WEATHER…………………………………………….17

o REFERENCES……………………………………..18

1. WHAT IS THE STRAIT OF GIBRALTAR?

The Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Gibraltar and Peninsular Spain in Europe from Morocco and Ceuta (Spain) in Africa. The name comes from the Rock of Gibraltar, which in turn originates from the Arabic "Tariq's mountain. It is also known as STROG (Strait Of Gibraltar) in naval use.

Europe and Africa are separated by 7.7 nautical miles (14.3 km) of ocean at the strait's narrowest point. The Strait's depth ranges

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between 300 and 900 metres (160 and 490 fathoms; 980 and 2,950 ft) which possibly interacted with the lower mean sea level of the last major glaciation 20,000 years ago when the level of the sea is believed to have been lower by 110–120 m (60–66 fathoms; 360–390 ft). Ferries cross between the two continents every day in as little as 35 minutes.

2. LOCATION

On the northern side of the Strait are Spain and Gibraltar (a British overseas territory in the Iberian Peninsula), while on the southern side are Morocco and Ceuta (a Spanish exclave in North Africa). Its boundaries were known in antiquity as the Pillars of Hercules. There are several islets, such as the disputed Isla Perejil, that are claimed by both Morocco and Spain.

Extension

The International Hydrographic Organization defines the limits of the Strait of Gibraltar as follows:

o On the West. A line joining Cape Trafalgar to Cape Spartel.

o On the East. A line joining Europa Point to Punta Almina.

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3. GEOLOGY

Around 5.9 million years ago, the connection between the Mediterranean Sea and the Atlantic Ocean along the Betic and Rifan Corridor was progressively restricted until its total closure, effectively causing the salinity of the Mediterranean to periodically rise within the gypsum and salt deposition range, during what is known as the Messinian salinity crisis. In this water chemistry environment, dissolved mineral concentrations, temperature and stilled water currents combined properly and occurred regularly to precipitate many mineral salts in sea floor bedded layers. The resultant accumulation of various huge salt and mineral deposits about the Mediterranean basin are directly linked to this era. It is believed that this process took a short time, by geological standards, lasting between 500,000 and 600,000 years.

After a lengthy period of restricted intermittent or no water exchange between the Atlantic Ocean and Mediterranean basin, approximately 5.33 million years ago, the Atlantic-Mediterranean connection was completely reestablished through the Strait of Gibraltar by the Zanclean Flood, and has remained open ever since. The erosion

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produced by the incoming waters seems to be the main cause for the present depth of the strait (900 m at the narrows, 280 m at the Camarinal Sill).

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4. FLOW AND WAVE PATTERNS

The Strait of Gibraltar links the Atlantic Ocean directly to the Mediterranean Sea. This direct linkage creates certain unique flow and wave patterns. These unique patterns are created due to the interaction of various regional and global evaporative forces, tidal forces, and wind forces.

Inflow and outflowThrough the strait, water generally flows more

or less continually in both an eastward and a westward direction. A smaller amount of deeper saltier and therefore denser waters continually work their way westwards (the Mediterranean outflow), while a larger amount of surface waters with lower salinity and density continually work their way eastwards (the Mediterranean inflow). These general flow tendencies may be occasionally interrupted for brief periods to accommodate temporary tidal flow requirements, depending on various lunar and solar alignments. Still, on the whole and over time, the balance of the water flow is eastwards, due to an evaporation rate within the Mediterranean basin higher than

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the combined inflow of all the rivers that empty into it. The shallow Camarinal Sill of the Strait of Gibraltar, which forms the shallowest point within the strait, acts to limit mixing between the cold, less saline Atlantic water and the warm Mediterranean waters. The Camarinal Sill is located at the far western end of the strait.

The Mediterranean waters are so much saltier than the Atlantic waters that they sink below the constantly incoming water and form a highly saline ( thermohaline , both warm and salty) layer of bottom water. This layer of bottom-water constantly works its way out into the Atlantic as the Mediterranean outflow. On the Atlantic side of the strait, a density boundary separates the Mediterranean outflow waters from the rest at about 100 m (330 ft) depth. These waters flow out and down the continental slope, losing salinity, until they begin to mix and equilibrate more rapidly, much further out at a depth of about 1,000 m (3,300 ft). The Mediterranean outflow water layer can be traced for

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thousands of kilometres west of the strait, before completely losing its identity.

Internal wavesWaves at the density boundary layer are

often produced by the strait. Like traffic merging on a highway, the water flow is constricted in both directions because it must pass over the Camarinal Sill. When large tidal flows enter the Strait and the high tide relaxes, internal waves are generated at the Camarinal Sill and proceed eastwards. Even though the waves may occur down to great depths, occasionally the waves are almost imperceptible at the surface, at other times they can be seen clearly in satellite imagery. These internal waves continue to flow eastward and to refract around coastal features. They can sometimes be traced for as much as 100 km, and sometimes create interference patterns with refracted waves.

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5. THE ATLANTIC OCEAN

Water Characteristics

On average, the Atlantic is the saltiest major ocean; surface water salinity in the open ocean ranges from 33 to 37 parts per thousand (3.3 – 3.7%) by mass and varies with latitude and season. Evaporation, precipitation, river inflow and sea ice melting influence surface salinity values. Although the lowest salinity values are just north of the equator (because of heavy tropical rainfall), in general the lowest values are in the high latitudes and along coasts where large rivers enter. Maximum salinity values occur at about 25° north and south, in subtropical regions with low rainfall and high evaporation.

Surface water temperatures, which vary with latitude, current systems, and season and reflect the latitudinal distribution of solar energy, range from below −2 °C (28 °F) to over 30 °C (86 °F). Maximum temperatures occur north of the equator, and minimum values are found in the Polar Regions. In the middle latitudes, the area of maximum temperature variations, values may vary by 7–8 °C (13–14 °F).

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The Coriolis effect circulates North Atlantic water in a clockwise direction, whereas South Atlantic water circulates counter-clockwise. The south tides in the Atlantic Ocean are semi-diurnal; that is, two high tides occur during each 24 lunar hours. In latitudes above 40° North some east-west oscillation occurs.

Climate

Climate is influenced by the temperatures of the surface waters and water currents as well as winds. Because of the ocean's great capacity to store and release heat, maritime climates are more moderate and have less extreme seasonal variations than inland climates. Precipitation can be approximated from coastal weather data and air temperature from water temperatures.

The oceans are the major source of the atmospheric moisture that is obtained through evaporation. Climatic zones vary with latitude; the warmest zones stretch across the Atlantic north of the equator. The coldest zones are in high latitudes, with the coldest regions corresponding to the areas covered by sea ice. Ocean currents influence climate by transporting warm and cold waters to other regions. The winds

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that are cooled or warmed when blowing over these currents influence adjacent land areas.

The Gulf Stream and its northern extension towards Europe, the North Atlantic Drift, for example, warms the atmosphere of the British Isles and north-western Europe and influences weather and climate as far south as the northern Mediterranean. The cold-water currents contribute to heavy FOG off the coast of eastern Canada (the Grand Banks of Newfoundland area) and Africa's northwestern coast. In general, winds transport moisture and air over land areas. Hurricanes develop in the southern part of the North Atlantic Ocean.

6. THE MEDITERRANIAN SEA

Oceanography

Being nearly landlocked affects conditions in the Mediterranean Sea: for instance, tides are very limited as a result of the narrow connection with the Atlantic Ocean. The Mediterranean is characterised and immediately recognised by its deep blue colour.

Evaporation greatly EXCEEDS precipitation and river runoff in the Mediterranean, a fact that is central to the water circulation within the basin. Evaporation is especially high in its eastern half, causing the water level to decrease and salinity to

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increase eastward. The salinity at 5 m depth is 3.8%.

The pressure gradient pushes relatively cool, low-salinity water from the Atlantic across the basin; it warms and becomes saltier as it travels east, then sinks in the region of the Levant and circulates westward, to spill over the Strait of Gibraltar. Thus, seawater flow is EASTWARD in the Strait's SURFACE waters, and WESTWARD BELOW.

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Strait of Gibraltar sea temperature (Cº)

Jan 16Feb 15Mar 16Apr 16May 17Jun 20Jul 22

Aug 22Sep 22Oct 20Nov 18Dec 17YEA

R18.4

Atlantic sea temp VS Mediterranean sea temp

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Here we can compare easily this huge difference.

7. WINDS IN THE STRAIT OF GIBRALTAR

Most common wind in the Strait of Gibraltar is Levant.

Levant

The Levant is an easterly wind that blows in the western Mediterranean Sea and southern France, an example of mountain-gap wind. In the western Mediterranean, particularly when the wind blows through the Strait of Gibraltar, it is called the Viento de Levante or the Levanter.

The wind rises in the central Mediterranean or around the Balearic Islands and blows westwards reaching its greatest intensity through the Strait of Gibraltar. The winds are moist carrying fog and precipitation in the eastern side of the Strait, but dry in the western side, as the moisture

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rains on the mountains between Algeciras and Tarifa. The winds are well known for creating a particular cloud formation above the Rock of Gibraltar; In Almería, the winds are well known for making the temperatures rise as the wind blows across the desert interior of the province. The Levanter winds can occur at any time in the year, but are most common from May to October, when the Mediterranean is comparatively cool, increasing the stability of the low-level airflow.

Strong gap winds can produce dangerous seas, especially when they blow against tide, current or swell through the Strait.

Levanter can produce winds of 20-40 kt (10-20 m/s) in and to the west of the gap when there is higher pressure to the east, over the Mediterranean, with lower pressure to the west of Gibraltar.

Synoptically, Levante can occur in three ways:(a) High pressure over Western Europe and low

pressure to the southwest of Gibraltar over the Atlantic or to the south over Morocco.

(b) High pressure cell over the Balearic Islands (Levante will be localized around the Strait).

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(c) An approaching cold front from the west toward the Strait of Gibraltar. As it usually occurs within stable air under an inversion the Levanter is often, but not always, accompanied by local low clouds, fog, haze and sometimes light rains.

The

Gibraltar levanter cloud

Sometimes the levanter forms a characteristic cloud over the Rock of Gibraltar. However, this is not always the case and a particular set of conditions is required for its formation.

Near the surface, the levanter is moist, but is unsaturated. As the moist air, which must be capped to be stable and so unable to rise by convection, is forced to rise over the Rock, the

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moisture condenses to form a cloud which streams away west from its top. If wind speeds are too low and stability high in the near-surface layer, the cloud does not form and condensation is also sensitive to small changes in moisture content, such that when the wind across the Rock veers into the southeast, the flow becomes too dry for the cloud to form, bringing drier air from North Africa. When the wind speed is too low, the air is blocked and unable to rise to form the cloud. At high wind speeds, the turbulent mixing to the lee of the Rock distributes the moisture through a comparatively deep layer and the cloud is, at best, very broken. Often it dissolves immediately west of the Rock in these turbulent windy conditions.

In suitable conditions, the characteristic "pennant" cloud forms downwind. It usually extends about 5 km west from the top of the Rock in a turbulent plume. This cloud hangs over the centre of the city of Gibraltar, while there is usually sunny weather in to the north and south from the southern outskirts of the city.

On the western side of the Rock, the winds near sea level are often from the west or southwest, as the air forms large overturning rolls, more than 350 m deep in the lee protection of the mountain, but strong winds tend to alter this flow regime.

The pennant cloud is not seen in westerly winds, although many of the same processes occur - it is just that the air is usually drier and may be warmer, as well as being less stable - so that convection from the surface is deeper and not capped near the mountaintop level. (Low cloud can sometimes be seen on the Rock, early in the

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morning in westerly winds, but this disappears as temperatures rise. It is also likely that the very steep eastern slope of the Rock tends to make the downwind flow too turbulent for cloud formation.)

Around dawn, the flow is relatively smooth through the cloud, but later in the morning, as it becomes warmer, some convective overturning develops within the plume as temperatures rise.

Formation of the cloud is classically very near the top of the ridge-line of the Rock at nearly 400 m altitude, but the base is usually a little lower in the turbulent flow to the west. The top of the cloud is rarely much more than 450 m above Gibraltar Bay.

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8. WEATHER

The climate of Gibraltar is temperate. During the winter months the prevailing wind is from the west often north-west and occasionally south-west. Snow or frost is extremely rare. Rain in the winter

can be heavy, but is rare after the spring.The mean minimum and maximum temperatures during this period are 13°C and 18°C respectively.

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R EFERENCES

https://en.wikipedia.org/wiki/Strait_of_Gibraltar https://en.wikipedia.org/wiki/

Thermohaline_circulation http://www.ercim.eu/publication/Ercim_News/

enw61/pares.html https://www.youtube.com/watch?

v=x7GXLJQ2Zn0 http://efdl.as.ntu.edu.tw/research/diecast/

medina2.html http://clasticdetritus.com/2007/12/16/sea-floor-

sunday-7-bathymetry-of-northeastern-atlantic-ocean/

http://oceano.uma.es/proyectosref.php? Id=5&i=2

http://wwwdas.uwyo.edu/~geerts/cwx/notes/ chap11/mow.html

http://www.gibnet.com/weather.htm https://books.google.es/books?

id=_fknAAAAQBAJ&pg=PA57&lpg=PA57&dq=meteorology+strait+of+gibraltar&source=bl&ots=OMw69iY2lC&sig=hn1vntsKLd8WmLU6tATcoCmeq5Q&hl=es&sa=X&ved=0CGwQ6AEwCWoVChMImv68x9r7xgIVR7oUCh3v-A29#v=onepage&q=meteorology%20strait%20of%20gibraltar&f=false

https://en.wikipedia.org/wiki/Levant_(wind) https://en.wikipedia.org/wiki/Mountain-gap_wind https://www.flickr.com/photos/davidparody/

page20 https://en.wikipedia.org/wiki/Atlantic_Ocean https://en.wikipedia.org/wiki/Mediterranean_Sea

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https://en.wikipedia.org/wiki/Thermohaline_circulation

https://en.wikipedia.org/wiki/Thermohaline_circulation


https://www.ghrsst.org/science-and- applications/applications/travel-and-tourism/

http://www.weatheronline.co.uk/reports/wind/ Levante.htm

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