Excitement is the oscillatory movement of water. It is perceived by the observer as the movement of waves on the surface of the water. In fact, the water surface oscillates up and down from the average level of the equilibrium position. The shape of waves during waves is constantly changing due to the movement of particles along closed, almost circular orbits.

Each wave is a smooth combination of elevations and depressions. The main parts of a wave are: crest- the highest part; sole - the lowest part; slope - profile between the wave crest and wave trough. The line along the crest of a wave is called wave front(Fig. 1).

Rice. 1. The main parts of the wave

The main characteristics of waves are height - the difference between the levels of the crest and bottom of the wave; length - the shortest distance between adjacent crests or wave bottoms; steepness - the angle between the wave slope and the horizontal plane (Fig. 1).

Rice. 1. Main characteristics of the wave

Waves have very high kinetic energy. The higher the wave, the more kinetic energy it contains (in proportion to the square of the increase in height).

Under the influence of the Coriolis force, on the right downstream, far from the mainland, a water wall appears, and a depression is created near the land.

By origin waves are divided as follows:

• friction waves;
• baric waves;
• seismic waves or tsunamis;
• seiches;
• tidal waves.

Friction waves

Friction waves, in turn, can be wind(Fig. 2) or deep. wind waves arise as a result of wind waves friction at the border of air and water. The height of wind waves does not exceed 4 m, but during strong and protracted storms it increases to 10-15 m and higher. The highest waves - up to 25 m - are observed in the westerly winds of the Southern Hemisphere.

Rice. 2. Wind waves and surf waves

Pyramidal, high and steep wind waves are called crowd. These waves are inherent in the central regions of cyclones. When the wind subsides, the excitement takes on character swell, i.e. unrest by inertia.

Primary form of wind waves - ripples. It occurs when the wind speed is less than 1 m / s, and at a speed greater than 1 m / s, first small, and then larger waves are formed.

A wave near the coast, mainly in shallow water, based on translational movements, is called surf(see Fig. 2).

deep waves occur at the boundary of two water layers with different properties. They often occur in straits, with two levels of flow, near river mouths, at the edge of melting ice. These waves mix sea water and are very dangerous for sailors.

baric wave

baric waves occur due to the rapid change in atmospheric pressure in the places of origin of cyclones, especially tropical ones. Usually these waves are single and do not cause much harm. The exception is when they coincide with high tide. The Antilles, the Florida peninsula, the coasts of China, India, and Japan are most often subjected to such disasters.

Tsunami

seismic waves occur under the influence of underwater tremors and coastal earthquakes. These are very long and low waves in the open ocean, but the force of their propagation is quite large. They move at a very high speed. Near the coasts, their length is reduced, and the height increases sharply (on average, from 10 to 50 m). Their appearance entails human casualties. First, the sea retreats several kilometers from the shore, gaining strength for a push, and then the waves splash onto the shore with great speed with an interval of 15-20 minutes (Fig. 3).

Rice. 3. Tsunami transformation

The Japanese called seismic waves tsunami, and the term is used all over the world.

The seismic belt of the Pacific Ocean is the main area of ​​tsunami formation.

seiches

seiches are standing waves that occur in bays and inland seas. They occur by inertia after the termination of the action of external forces - wind, seismic shocks, sudden changes, intense precipitation, etc. At the same time, water rises in one place, and falls in another.

Tidal wave

tidal waves- These are movements made under the influence of the tide-forming forces of the Moon and the Sun. The reverse reaction of sea water to the tide - low tide. The strip drained at low tide is called drying.

There is a close connection between the height of the tides and the tides with the phases of the moon. New moons and full moons have the highest tides and lowest tides. They're called syzygy. At this time, the lunar and solar tides, advancing simultaneously, overlap each other. Between them, on the first and last Thursdays of the moon phases, the lowest, quadrature tides.

As already mentioned in the second section, in the open ocean the height of the tide is small - 1.0-2.0 m, and near the dissected coast it increases sharply. The tide reaches its maximum value on the Atlantic coast of North America, in the Bay of Fundy (up to 18 m). In Russia, the maximum tide of 12.9 m was recorded in Shelikhov Bay (Sea of ​​Okhotsk). In inland seas, tides are hardly noticeable, for example, in the Baltic Sea near St. Petersburg, the tide is 4.8 cm, but along some rivers, the tide can be traced hundreds and even thousands of kilometers from the mouth, for example, in the Amazon - up to 1400 cm.

A steep tidal wave rising up a river is called boron. In the Amazon, boron reaches a height of 5 m and is felt at a distance of 1400 km from the mouth of the river.

Even with a calm surface, there is excitement in the thickness of the ocean waters. These are the so-called internal waves - slow, but very significant in scope, sometimes reaching hundreds of meters. They arise as a result of external action on a vertically heterogeneous mass of water. In addition, since the temperature, salinity and density of ocean water do not change gradually with depth, but abruptly from one layer to another, specific internal waves arise at the boundary between these layers.

sea ​​currents

sea ​​currents- these are horizontal translational movements of water masses in the oceans and seas, characterized by a certain direction and speed. They reach several thousand kilometers in length, tens to hundreds of kilometers wide, hundreds of meters deep. According to the physical and chemical properties of the waters of sea currents, they are different from those around them.

By duration of existence (stability) sea ​​currents are divided as follows:

• permanent that pass in the same areas of the ocean, have one general direction, more or less constant speed and stable physico-chemical properties of the transported water masses (North and South trade winds, Gulf Stream, etc.);
• periodical, in which the direction, speed, temperature are subject to periodic laws. They occur at regular intervals in a certain sequence (summer and winter monsoon currents in the northern part of the Indian Ocean, tidal currents);
• temporary most often caused by winds.

By temperature sign sea ​​currents are

• warm which have a temperature higher than the surrounding water (for example, the Murmansk current with a temperature of 2-3 ° C among waters of about ° C); they have a direction from the equator to the poles;
• cold, the temperature of which is lower than the surrounding water (for example, the Canary Current with a temperature of 15-16 ° C among waters with a temperature of about 20 ° C); these currents are directed from the poles to the equator;
• neutral, which have a temperature close to the environment (for example, equatorial currents).

According to the depth of location in the water column, currents are distinguished:

• superficial(up to 200 m depth);
• subsurface having a direction opposite to the surface;
• deep, the movement of which is very slow - of the order of several centimeters or a few tens of centimeters per second;
• bottom, regulating the exchange of water between the polar - subpolar and equatorial-tropical latitudes.

By origin distinguish the following currents:

• frictional, which can be drift or wind. Drift ones arise under the influence of constant winds, and wind ones are created by seasonal winds;
• gradient gravity, among which are stock, resulting from the slope of the surface caused by excess water due to their inflow from the ocean and heavy rainfall, and compensatory, which arise due to the outflow of water, scarce precipitation;
• inert, which are observed after the termination of the action of the factors that excite them (for example, tidal currents).

The system of ocean currents is determined by the general circulation of the atmosphere.

If we imagine a hypothetical ocean that continuously stretches from the North Pole to the South, and impose a generalized scheme of atmospheric winds on it, then, taking into account the deflecting Coriolis force, we get six closed rings -
gyres of sea currents: Northern and Southern equatorial, Northern and Southern subtropical, Subarctic and Subantarctic (Fig. 4).

Rice. 4. Cycles of sea currents

Deviations from the ideal scheme are caused by the presence of continents and the peculiarities of their distribution over the earth's surface. However, as in the ideal scheme, in reality, on the surface of the ocean there is zonal shift large - several thousand kilometers long - not completely enclosed circulation systems: it is equatorial anticyclonic; tropical cyclonic, northern and southern; subtropical anticyclonic, northern and southern; Antarctic circumpolar; high latitude cyclonic; arctic anticyclonic system.

In the Northern Hemisphere they move clockwise, in the Southern Hemisphere they move counterclockwise. Directed from west to east equatorial inter-trade countercurrents.

In the temperate subpolar latitudes of the Northern Hemisphere, there are small rings of currents around baric lows. The movement of water in them is directed counterclockwise, and in the Southern Hemisphere - from west to east around Antarctica.

The currents in zonal circulation systems can be traced quite well down to a depth of 200 m. With depth, they change direction, weaken and turn into weak eddies. Instead, meridional currents intensify at depth.

The most powerful and deepest of the surface currents play an important role in the global circulation of the oceans. The most stable surface currents are the North and South trade winds of the Pacific and Atlantic Oceans and the South trade winds of the Indian Ocean. They are oriented from east to west. Tropical latitudes are characterized by warm sewage currents, such as the Gulf Stream, Kuroshio, Brazil, etc.

Under the influence of constant westerly winds in temperate latitudes, there are warm North Atlantic and North Atlantic

The Pacific Current in the Northern Hemisphere and the cold (neutral) course of the Western Winds in the Southern Hemisphere. The latter forms a ring in three oceans around Antarctica. The large circulations in the Northern Hemisphere are closed by cold compensatory currents: along the western coasts in tropical latitudes - California, Canary, and in the Southern - Peruvian, Bengal, Western Australian.

The most famous currents are also the warm Norwegian Current in the Arctic, the cold Labrador Current in the Atlantic, the warm Alaska Current and the cold Kurile-Kamchatka Current in the Pacific Ocean.

Monsoon circulation in the northern part of the Indian Ocean generates seasonal wind currents: winter - from east to west and summer - from west to east.

In the Arctic Ocean, the direction of movement of water and ice occurs from east to west (Transatlantic Current). The reasons for it are the abundant river flow of the rivers of Siberia, the rotational cyclonic movement (counterclockwise) over the Barents and Kara Seas.

In addition to circulation macrosystems, there are open ocean eddies. Their size is 100-150 km, and the speed of movement of water masses around the center is 10-20 cm/s. These mesosystems are called synoptic vortices. It is believed that it is in them that at least 90% of the kinetic energy of the ocean is contained. Vortices are observed not only in the open ocean, but also in marine currents such as the Gulf Stream. Here they rotate at an even higher speed than in the open ocean, their ring system is better expressed, which is why they are called rings.

For the climate and nature of the Earth, especially coastal areas, the importance of sea currents is great. Warm and cold currents maintain the temperature difference between the western and eastern coasts of the continents, disrupting its zonal distribution. Thus, the non-freezing port of Murmansk is located beyond the Arctic Circle, and on the east coast of North America, the Gulf of St. Lawrence (48°N). Warm currents contribute to precipitation, cold currents, on the contrary, reduce the possibility of precipitation. Therefore, areas washed by warm currents have a humid climate, and cold ones have a dry one. With the help of sea currents, migration of plants and animals, the transfer of nutrients and gas exchange are carried out. Currents are also taken into account when sailing.

They play an important role in shaping the climate on planet Earth, and are also largely responsible for the diversity of flora and fauna. Today we will get acquainted with the types of currents, the reason for their occurrence, consider examples.

It's no secret that our planet is washed by four oceans: the Pacific, Atlantic, Indian and Arctic. Naturally, the water in them cannot be stagnant, as this would have led to an ecological disaster long ago. Due to the fact that it constantly circulates, we can fully live on Earth. Below is a map of ocean currents, it clearly shows all the movements of water flows.

What is ocean current?

The course of the World Ocean is nothing more than the continuous or periodic movement of large masses of water. Looking ahead, we will immediately say that there are many of them. They differ in temperature, direction, depth passage and other criteria. Ocean currents are often compared to rivers. But the movement of river flows occurs only downward under the influence of gravitational forces. But the circulation of water in the ocean occurs due to many different reasons. For example, wind, uneven density of water masses, temperature difference, the influence of the Moon and the Sun, pressure changes in the atmosphere.

Causes

I would like to start my story with the reasons that give rise to the natural circulation of water. There is practically no exact information even at the present time. This is explained quite simply: the ocean system has no clear boundaries and is in constant motion. Now the currents that are closer to the surface have been studied in more depth. To date, one thing is known for sure, that the factors affecting the circulation of water can be both chemical and physical.

So, consider the main causes of ocean currents. The first thing I want to highlight is the effect of air masses, that is, wind. It is thanks to him that surface and shallow currents function. Of course, the wind has nothing to do with the circulation of water at great depths. The second factor is also important, it is the impact of outer space. In this case, the currents arise due to the rotation of the planet. And finally, the third main factor that explains the causes of ocean currents is the different density of water. All streams of the World Ocean differ in temperature, salinity and other indicators.

Directional factor

Depending on the direction, the ocean water circulation flows are divided into zonal and meridional. The first move to the west or to the east. Meridional currents go south and north.

There are also other types that are caused. Such ocean currents are called tidal. They have the greatest strength in shallow waters in the coastal zone, at the mouths of rivers.

Currents that do not change strength and direction are called stable, or settled. These include such as the North trade wind and the South trade wind. If the movement of the water flow changes from time to time, then it is called unstable, or unsettled. This group is represented by surface currents.

surface currents

The most noticeable of all are the surface currents, which are formed due to the influence of the wind. Under the influence of the trade winds, constantly blowing in the tropics, huge streams of water are formed in the equator region. It is they who form the North and South equatorial (trade wind) currents. A small part of these turns back and forms a countercurrent. The main streams deviate to the north or south when they collide with the continents.

Warm and cold currents

Types of ocean currents play an important role in the distribution of climatic zones on Earth. It is customary to call warm streams of the water area that carry water with a temperature above zero. Their movement is characterized by the direction from the equator to high geographical latitudes. These are the Alaska Current, Gulf Stream, Kuroshio, El Niño, etc.

Cold streams carry water in the opposite direction compared to warm ones. Where a current with a positive temperature meets on their way, an upward movement of water occurs. The largest are the Californian, Peruvian, etc.

The division of currents into warm and cold is conditional. These definitions reflect the ratio of the water temperature in the surface layers to the ambient temperature. For example, if the flow is colder than the rest of the water mass, then such a flow can be called cold. Otherwise, it is considered

Ocean currents largely determine our planet. Constantly mixing the water in the World Ocean, they create conditions favorable for the life of its inhabitants. And our lives directly depend on it.

Continuous movement is one of the most striking features of ocean waters. No wonder the motto of the submarine "Nautilus" in the famous novel by Jules Verne was the phrase: "Mobile in the mobile." You have already met in the 6th grade course with the types of water movements in the ocean - waves, ebbs and flows.

In the oceans and seas, huge streams of water tens and hundreds of kilometers wide and several hundred meters deep move in certain directions over distances of thousands of kilometers. Such flows - "rivers in the oceans" - are called oceanic (sea) currents. They move at a speed of 1-3 km/h, sometimes up to 9 km/h.

Theme: Hydrosphere

Lesson:surface currents

Today we will learn:

On the causes of the formation of ocean currents;

On the role of ocean currents in the redistribution of heat and moisture on the planet.

There are several reasons for causing currents: for example, heating and cooling of the water surface, precipitation and evaporation, differences in water density, but the most significant role in the formation of currents is the role of the wind (see Fig. 1). Currents in the direction prevailing in them are divided into zonal, going to the west and east, and meridional - carrying their waters to the north or south. latitudes +20, in temperate latitudes from 0 to -25 degrees, and in arctic latitudes from -20 to -40. (This sentence needs to start somehow, I guess.)

Under the influence of constant winds (trade winds and westerly winds of temperate latitudes), surface currents arise.

Currents carry heat from one area of ​​the World Ocean to another and ensure the exchange of oxygen between ocean water and the atmosphere.

The formation of the circulation of currents begins with the action of the trade winds in equatorial latitudes.

Rice. 1. Currents in the oceans

Currents deviate from rectilinear motion by the action of the Coriolis force (we will talk about it in the next topic): in the Northern Hemisphere - clockwise, in the Southern - in the opposite direction ().

Thermohaline circulation

In such regions of the World Ocean as the Labrador Sea, the North Sea and the Weddell Sea, cooled water with high salinity descends from the surface to a depth of several hundred meters and begins to move in the opposite direction with respect to the water masses on the surface. It's like a conveyor belt. Such thermohaline (i.e., determined by temperature and salinity) circulation is a typical phenomenon for the entire area of ​​the World Ocean ().

The more the Sun heats the ocean, the more water evaporates from the surface and the higher the concentration of salts. The winds drive the heavy water masses towards the poles, while the water cools down and partially freezes at the pole.

Due to freezing and evaporation, salinity still increases, and with it, the density of water also increases. It descends and generates a deep countercurrent (see Fig. 2). At the equator, cold water, gradually mixing with the upper layers, rises again to the surface.

Rice. 2. Equatorial countercurrent ()

Thus, a regularity is observed in the distribution of currents in the ocean. The general scheme of currents coincides with the scheme of constant winds.

Sea (oceanic) currents have a significant impact on the climate. Sea (oceanic) currents play an important role in the process of interlatitudinal heat transfer, which means that they affect the climate of certain regions of the Earth.

For example, the famous Gulf Stream, passing into the North Atlantic Current, carries heat to Northern and Northwestern Europe (see Fig. 3). The speed of the Gulf Stream is approximately 5.5 km / h - compare with deep currents, which move only a few meters a day. Without this warm current, Europeans would freeze.

Rice. 3. Scheme of the Gulf Stream

It is interesting

Closed eddy currents in the ocean

In addition to rings, the occurrence of which is associated with meanders of powerful jet currents (such as the Gulf Stream, Kuroshio, etc.), closed vortex flows are formed in the open ocean as a result of various wave disturbances, the interaction of water mass flows of different directions, velocities, densities and other properties, atmospheric processes over the ocean, etc. The existence of eddies in the open ocean was first discovered and studied in detail in the seventies by Soviet oceanologists. In cyclonic eddies of both types in the central regions, deep waters rise to the surface, and in anticyclonic eddies, surface waters sink.

According to modern concepts, ocean eddies are water cycles up to 400 km in diameter, which capture its thickness from the surface to a depth of one and a half kilometers, rotating at a speed of up to 50 cm / s. They move at a speed of about 10 km/day, changing their configuration.

Homework

Read § 7. Do the practical work. Using the physical map of the oceans in the contour map, plot and label the North Atlantic and South Atlantic Gyres.

Bibliography

MainI

1. Geography. Earth and people. Grade 7: Textbook for general education. uch. / A.P. Kuznetsov, L.E. Savelyeva, V.P. Dronov, "Spheres" series. - M.: Education, 2011.

2. Geography. Earth and people. Grade 7: atlas, series "Spheres".

Additional

1. N.A. Maksimov. Behind the pages of a geography textbook. - M.: Enlightenment.

Literature for preparing for the GIA and the Unified State Examination

1. Tests. Geography. Grades 6-10: Teaching aid / A. A. Letyagin. - M .: LLC "Agency" KRPA "Olimp": Astrel, AST, 2007. - 284 p.

2. Study guide for geography. Tests and practical tasks in geography / I. A. Rodionova. - M.: Moscow Lyceum, 1996. - 48 p.

3. Geography. Answers on questions. Oral exam, theory and practice / V. P. Bondarev. - M.: Publishing house "Exam", 2009. - 160 p.

4. Thematic tests to prepare for the final certification and the exam. Geography. - M.: Balass, ed. House of RAO, 2011. - 160 p.

1. Russian Geographical Society ().

3. Study guide for geography ().

4. Geographical directory ().

Surface currents are of the greatest geographical importance. They have a significant impact on the climate, and seafarers must reckon with them.

Previously, it was believed that the direction of surface currents coincided with the direction of the winds. In small bodies of water, this is true to some extent. But in the open ocean, where it is deep enough, the rotation of the Earth already affects, deviating the current from the direction of the winds in the Northern Hemisphere to the right, and in the Southern Hemisphere to the left.

Approaching the shore or shallow water from the open ocean, the current splits and changes direction. In cases where the shore is straight and the current is directed perpendicular to it, the current bifurcates into two identical jets. One jet goes to the right along the coast, and the other - to the left. Approaching the shore at an angle, the current splits into two jets of different sizes. A large jet goes along the coast towards an obtuse angle, and a smaller one - towards a sharp one. If the bank forms a ledge, then the current approaching it is cut by it into two jets passing to the right and left of the ledge.

The main surface currents are driven by the trade winds that blow over the oceans all year round.

Consider the currents of the Pacific Ocean. The current caused by the northeast trade wind forms an angle of 45 ° with it, deviating to the right from the prevailing wind direction. Therefore, the current is directed from east to west along the equator, somewhat north of it (arrow 1). This current owes its existence to the northeast trade wind. It is called the North trade wind.

The southeast trade wind creates the South trade wind current (arrow 2), deviating from the direction of the trade wind to the left by 45 °. It is directed in the same way as the previous one, from east to west, but passes south of the equator.

Both trade winds (equatorial) currents, running parallel to the equator, reach the eastern coast of the continents and bifurcate, with one jet leaving along the coast to the north, and the other to the south. In the drawing, these branches are indicated by arrows 3,4,5 and 6. The southern branch of the North trade wind current (arrow 4) and the northern branch of the South trade wind current (arrow 6) go towards each other. Having met, they merge and move along the zone of equatorial calm from west to east (arrow 7), forming an equatorial countercurrent. It is very well expressed in the Pacific Ocean.

The right branch of the Northern Trade Wind (arrow 3) goes north along the eastern coast of the mainland. Under influence. of the Earth's rotation, it gradually deviates to the right, pushes away from the coast, and near the 40th parallel goes east into the open ocean (arrow 5). Here it is picked up by southwesterly winds and forced to twitch in directions from west to east. Having reached the western coast of the mainland, the current bifurcates, its right branch (arrow 9) goes to the south, being deviated by the rotation of the Earth to the right, and therefore is squeezed out from the coast. Having reached the Northern trade wind (equatorial) current, this branch merges with it and forms a closed northern equatorial ring of currents (arrows 1, 3, 8, and 9).

The left branch of the current (arrow 10) goes to the north, is deflected by the rotation of the Earth to the right, presses against the western coast of the mainland and therefore follows the bends of the coast and the features of the bottom topography. This current carries high salinity water from the subtropics. Having met with colder, but less salty polar water, it goes into the depths.

Northeasterly winds blowing from the circumpolar space also create a current (arrow 11). It, carrying very cold water, goes south along the eastern shores of the Eurasian continent.

In the Southern Hemisphere, the left branch of the Southern Trade Wind Current (arrow 5) is directed south along the eastern coast of Australia, is deflected to the left by the rotation of the Earth and pushed away from the coast. Near the 40th parallel (as well as in the Northern Hemisphere), it goes into the open ocean, is picked up by northwest winds and moves from west to east (arrow 12). At the western coast of America, the current bifurcates. The left branch goes along the coast of the mainland to the north. Deviated by the rotation of the Earth to the left, this current (arrow 13) is pushed away from the coast and merges with the South Trade Wind Current, forming a southern equatorial ring of currents, similar to the northern one (arrows 2, 5, 12 and 13). The right branch (arrow 14), past the southern tip of America, goes east into the neighboring ocean. Obviously, a similar current should also enter from the west from the neighboring ocean through the strait (arrow 15).

Consider a physical map of the world showing currents. It will not be difficult for you to understand why the Pacific and Atlantic oceans have two equatorial current rings - north and south of the equator, and the Indian - only one in the Southern Hemisphere. North of the equator, the ocean space is not enough to form a ring of currents.

The map shows that in the Pacific and Atlantic oceans, the outlines of the western coasts and the numerous islands located near them create a more complex picture of the currents than shown in the diagram.

Let's move on to the scheme of currents in the Atlantic Ocean. Here the South trade wind (equatorial) current (arrow 2) is directed from the southern part of the Gulf of Guinea to the west between the equator and the 15th parallel. Approaching the ledge of the South American mainland, it is cut into two jets. The left branch of the current, shown by arrow 5 in the diagram, goes south along the coast of Brazil. This current is called the Brazilian. The right jet (arrow 6) continues to move west-northwest along the northern coast of South America, in particular near Guiana. This is the Guiana current. Through the straits between the Lesser Antilles, it enters the Caribbean Sea.

The northern trade wind (equatorial) current (arrow 1), starting at the Cape Verde Islands, goes westward between the 5th northern parallel and the northern tropic. Having met the Greater Antilles, it is cut by them. The southern branch (arrow 4) enters the Caribbean Sea, and then, together with the Guiana Current, into the Gulf of Mexico. The northern branch, called the Antilles Current, follows north of the Greater Antilles (arrow 3).

An excess of water is being created in the Gulf of Mexico. In addition to the waters of the Guiana and the southern branch of the Northern Trade Winds, 600 km3 of water flows here annually, which is brought by the Mississippi, one of the greatest rivers in the world, which flows into the Gulf of Mississippi. As a result, the water level of the Gulf of Mexico near the Florida Strait is higher than in the Atlantic Ocean. Therefore, through the Strait of Florida between Florida, Cuba and the Bahamas, a strong waste "current from the Gulf" rushes into the Atlantic Ocean - the Gulf Stream. The waters of the Antilles current join it from the east, making it even more powerful.

The Gulf Stream, deviating to the right, at Cape Hatteras leaves the coast of America and goes along the 40th parallel to the east into the open ocean (arrow 8). On the way to the Azores, its waters become saltier due to strong evaporation. Near the Azores, the Gulf Stream bifurcates. A smaller stream goes to the right, towards an acute angle, and, passing by the Canary Islands, gets the name of the Canary Current. It closes the northern equatorial ring of currents (arrow 9).

Inside this ring is the Sargasso Sea, the only sea that has no shores, as it is limited only by currents. The left, more powerful branch of the Gulf Stream, directed towards an obtuse angle, goes north, to the shores of Europe. This is the North Atlantic Current (arrow 10).

To the west of Ireland, along the underwater threshold, stretching from Iceland through the Faroe Islands to Scotland, a stream separates from it, going to Iceland. It forms the Irminger Current, which brings warm water to the southern and western shores of Iceland. That is why the sea never freezes off the coast of Iceland.

Most of the waters of the North Atlantic Current, having passed the underwater threshold, are pressed against Scandinavia by the rotation of the Earth. This is a warm Norwegian current, thanks to which the winter in Norway is mild. The sea and fiords here are always free of ice.

At the North Cape, the Norwegian Current splits. The left branch (Spitsbergen Current) runs along the shallow waters of the Barents Sea north to Spitsbergen, preventing the formation of ice off its western shores. The right branch (North Cape Current) enters the Barents Sea.

In the Arctic Ocean, there are currents going from the New Siberian Islands through the North Pole into the Atlantic Ocean. They bring trunks of Siberian trees to the shores of Greenland. Thanks to the same currents, objects from the ship Jeannette, crushed by ice, got into Greenland.

The main current here is the East Greenland, which runs along the eastern coast of Greenland.

It was it that carried away the ice floe with the first drifting station "North Pole". To the west of Greenland, in Baffin Bay, the very cold Labrador Current begins, carrying huge ice mountains - icebergs into the Atlantic Ocean.

In the Indian Ocean, south of the equator, the currents correspond to the current patterns of the Pacific and Atlantic oceans that we have considered. This can be seen by studying the map of the currents of the oceans.

IMPACT OF SEA CURRENTS ON CLIMATE AND NAVIGATION

Sea currents have a significant impact on the climate of the coastal parts of the continents. In both hemispheres between the equator and the 40th parallel, the eastern shores of the mainland are warmer than the western ones. In the temperate zone, the ratio is reversed: the eastern shores of the mainland are colder than the western ones. In the countries of Western Europe, winters are mild, and in areas of North America located at the same latitudes, they are severe.

The contrast between the relatively mild climate of Scandinavia and the climate of Greenland, covered with a thick layer of ice, is especially noticeable.

The study of sea currents is necessary for navigation. Even with a low speed of the equatorial currents of the Atlantic Ocean - from 20 to 65 km per day - it is necessary to take them into account. For a day, such a current can shift the ship from the accepted course by 40-50 km to the side.

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Introduction

Sea water is a very mobile medium, so in nature it is in constant motion. This movement is caused by various reasons and, above all, by the wind. It excites the surface currents in the ocean, which carry huge masses of water from one area to another. However, the direct influence of the wind extends over a relatively small (up to 300 m) distance from the surface. The mobility of the waters of the ocean is also manifested in vertical oscillatory movements - such as, for example, waves and tides. The latter are also associated with horizontal movements of water - tidal currents. Below in the water column and in the near-bottom horizons, the movement occurs slowly and has directions associated with the bottom topography.

The movement of the waters of the oceans

Fig.1.1

Surface currents form two large gyres separated by a countercurrent near the equator. The whirlpool of the northern hemisphere rotates clockwise, and the southern hemisphere - counterclockwise. When comparing this scheme with the currents of the real ocean, one can see a significant similarity between them for the Atlantic and Pacific oceans. At the same time, it is impossible not to notice that the real ocean has a more complex system of countercurrents near the boundaries of the continents, where, for example, the Labrador Current (North Atlantic) and the Alaska Return Current (Pacific Ocean) are located. In addition, the currents near the western margins of the oceans are characterized by higher speeds of water movement than those of the eastern ones. The winds apply a couple of forces to the surface of the ocean, rotating the water in the northern hemisphere clockwise, and in the southern hemisphere - against it. Large eddies of ocean currents result from this pair of rotating forces. It is important to emphasize that winds and currents are not one-to-one. For example, the presence of the fast Gulf Stream off the western shores of the North Atlantic does not mean that particularly strong winds blow in this area. The balance between the rotating pair of forces of the mean wind field and the resulting currents is formed over the area of ​​the entire ocean. In addition, currents accumulate a huge amount of energy. Therefore, a shift in the mean wind field does not automatically lead to a shift in large oceanic eddies.

Whirlpools driven by the wind are superimposed by another circulation, thermohaline ("halina" - salinity). Together, temperature and salinity determine the density of water. The ocean transports heat from tropical to polar latitudes. This transport is carried out with the participation of such large currents as the Gulf Stream, but there is also a return flow of cold water towards the tropics. It occurs mainly at depths below the layer of wind-driven whirlpools. Wind and thermohaline circulations are components of the general circulation of the ocean and interact with each other. So, if thermohaline conditions explain mainly the convective movements of water (the sinking of cold heavy water in the polar regions and its subsequent runoff to the tropics), then it is the winds that cause the divergence (divergence) of surface waters and actually “pump out” cold water back to the surface, completing the cycle .

Ideas about thermohaline circulation are less complete than about wind circulation, but some features of this process are more or less known. The formation of sea ice in the Weddell Sea and the Norwegian Sea is believed to be important for the formation of cold dense water spreading near the bottom in the South and North Atlantic. Both areas receive water of increased salinity, which cools down to freezing in winter. When water freezes, a significant part of the salts contained in it is not included in the newly formed ice. As a result, the salinity and density of the remaining unfrozen water increase. This heavy water sinks to the bottom. It is commonly referred to as Antarctic bottom water and North Atlantic deep water, respectively.

Another important feature of the thermohaline circulation is related to the density stratification of the ocean and its effect on mixing. The density of water in the ocean increases with depth and the lines of constant density are almost horizontal. Water with different characteristics is much easier to mix in the direction of lines of constant density than across them.

Thermohaline circulation is difficult to characterize with certainty. In fact, both horizontal advection (transport of water by sea currents) and diffusion must play an important role in the thermohaline circulation. Determining the relative importance of these two processes in any area or situation is an important task.

The main features of the surface circulation of the waters of the world ocean are determined by wind currents. It is important to note that the movement of water masses in the Atlantic and Pacific oceans is very similar. In both oceans, there are two huge anticyclonic circular currents separated by the equatorial countercurrent. In both oceans, there are, in addition, powerful western (in the northern hemisphere) boundary currents (Gulf Stream in the Atlantic and Kuroshio in the Pacific) and similar in nature, but weaker eastern currents (in the southern hemisphere) - Brazilian and East Australian. Along their western coasts, cold currents can be traced - Oyashio in the Pacific Ocean, Labrador and Greenland currents in the North Atlantic. In addition, a smaller-scale cyclonic gyre has been found in the eastern part of each basin north of the main gyre.

Some of the differences between the oceans are due to differences in the outlines of their basins. The Atlantic, Indian and Pacific Oceans are all different shapes. But some of the differences are determined by the features of the wind field, as, for example, in the Indian Ocean. The circulation in the southern part of the Indian Ocean is basically similar to the circulation in the southern basins of the Atlantic and Pacific oceans. But in the northern part of the Indian Ocean, it is clearly subject to monsoon winds, where during the summer and winter monsoons the circulation pattern changes completely.

For a number of reasons, as one approaches the coast, deviations from the general circulation pattern become more and more significant. As a result of the interaction of the main climatic characteristics of the currents with the same characteristics of the coasts, stable or quasi-stable eddies often arise. Noticeable deviations from the average circulation pattern can also cause local winds near the coasts. In some areas, the disturbing factors of the circulation regime are river runoff and tides.

In the central regions of the oceans, the average characteristics of the currents are calculated from a small amount of accurate data and are therefore especially unreliable.

water world ocean flow