Sea currents: interesting facts. ocean currents

In sailing directions sometimes only a brief, sometimes very detailed (with maps, diagrams, tables) verbal description of the waves is given, giving an idea of the magnitude and nature of the waves by the seasons of the year and in certain areas of the sea.

Atlases of physical and geographical data. They consist of a set of different maps characterizing the waves of a particular basin by months and seasons of the year. On these maps, "roses" in eight points show the frequency of wave and swell in direction and strength in individual squares of the ocean. The length of the rays on the scale determines the percentage of wave direction repeatability, and the numbers in the circles indicate the percentage of the absence of waves. In the lower corner of the square is the number of observations in this square.

Reference books and tables on waves. The manual contains tables of frequency of winds and waves, a table of the dependence of wave elements on wind speed, duration and length of wind acceleration, and also gives the values \u200b\u200bof the greatest heights, lengths and periods of waves. With the help of this table for areas of the high seas, it is possible to determine their height, period and duration of growth by wind speed (in m / s) and acceleration length (in km).

These benefits allow the navigator to correctly assess the navigation conditions and choose the most profitable and safe navigation routes, taking into account wind and waves.

Wave cards

Wave maps show the positions of synoptic objects

(cyclones, anticyclones with an indication of pressure in the center; atmospheric fronts), a picture of wave fields in the form of isolines of equal wave heights with digitization of their values and an indication of the propagation direction with a contour arrow, as well as a characteristic of wind and wave conditions at individual points of stations.

12. Causes of sea currents.sea currents called the translational movement of masses of water in the sea under the influence of natural forces. The main characteristics of currents are speed, direction and duration of action.

The main forces (causes) that cause sea currents are divided into external and internal. The external ones include wind, atmospheric pressure, tide-forming forces of the Moon and the Sun, and the internal ones include the forces arising from the uneven horizontal distribution of the density of water masses. Immediately after the onset of the movement of water masses, secondary forces appear: the Coriolis force and the friction force, which slows down any movement. The direction of the current is influenced by the configuration of the banks and the topography of the bottom.

13. Classification of sea currents.

Sea currents are classified:

According to the factors causing them, i.e.

1. By origin: wind, gradient, tidal.

2. By stability: constant, non-periodic, periodic.

3. According to the depth of location: surface, deep, near-bottom.

4. By the nature of the movement: rectilinear, curvilinear.

5. By physical and chemical properties: warm, cold, salty, fresh.

Origin currents are:

1 wind currents occur under the action of frictional force on the water surface. After the beginning of the action of the wind, the current speed increases, and the direction, under the influence of the Coriolis acceleration, deviates by a certain angle (in the northern hemisphere to the right, in the southern hemisphere - to the left).

2. Gradient flows are also non-periodic and caused by a number of natural forces. They are:

3. waste, associated with surge and surge of water. An example of a runoff current is the Florida Current, which is the result of the surge of waters into the Gulf of Mexico by the windy Caribbean Current. The excess waters of the bay rush into the Atlantic Ocean, giving rise to a powerful current. Gulfstream.

4. stock Currents are generated by the flow of river water into the sea. These are the Ob-Yenisei and Lena currents, penetrating hundreds of kilometers into the Arctic Ocean.

5. barometric currents arising due to uneven changes in atmospheric pressure over neighboring areas of the ocean and the associated increase or decrease in water levels.

By sustainability currents are:

1. Permanent - the vector sum of the wind and gradient currents is drift current. Examples of drift currents are the trade winds in the Atlantic and Pacific Oceans and the monsoons in the Indian Ocean. These currents are constant.

1.1. Powerful steady currents with speeds of 2-5 knots. These currents include the Gulf Stream, Kuroshio, Brazilian and Caribbean.

1.2. Constant currents with speeds of 1.2-2.9 knots. These are the North and South trade winds and the equatorial countercurrent.

1.3. Weak constant currents with speeds of 0.5-0.8 knots. These include the Labrador, North Atlantic, Canary, Kamchatka and California currents.

1.4. Local currents with speeds of 0.3-0.5 knots. Such currents for certain areas of the oceans in which there are no clearly defined currents.

2. Periodic flows - These are such currents, the direction and speed of which change at regular intervals and in a certain sequence. An example of such currents are tidal currents.

3. Non-periodic flows are caused by non-periodic action of external forces and, first of all, by the effects of wind and pressure gradient considered above.

By depth currents are:

Surface - currents are observed in the so-called navigation layer (0-15 m), i.e. layer corresponding to the draft of surface vessels.

The main reason for the occurrence superficial The currents in the open ocean is the wind. There is a close relationship between the direction and speed of the currents and the prevailing winds. Steady and continuous winds have a greater influence on the formation of currents than winds of variable directions or local ones.

deep currents observed at a depth between the surface and bottom currents.

bottom currents take place in the layer adjacent to the bottom, where friction against the bottom exerts a great influence on them.

The speed of movement of surface currents is highest in the uppermost layer. Deeper it goes down. Deep waters move much more slowly, and the speed of movement of bottom waters is 3–5 cm/s. The speed of the currents is not the same in different regions of the ocean.

According to the nature of the movement of the current, there are:

According to the nature of the movement, meandering, rectilinear, cyclonic and anticyclonic currents are distinguished. Meandering currents are called currents that do not move in a straight line, but form horizontal undulating bends - meanders. Due to the instability of the flow, meanders can separate from the flow and form independently existing eddies. Rectilinear currents characterized by the movement of water in relatively straight lines. Circular currents form closed circles. If the movement in them is directed counterclockwise, then these are cyclonic currents, and if clockwise, then they are anticyclonic (for the northern hemisphere).

By the nature of physical and chemical properties distinguish between warm, cold, neutral, saline and freshwater currents (the division of currents according to these properties is to a certain extent conditional). To assess the specified characteristic of the current, its temperature (salinity) is compared with the temperature (salinity) of the surrounding waters. Thus, a warm (cold) flow is a water temperature in which the temperature of the surrounding waters is higher (lower).

warm currents are called, in which the temperature is higher than the temperature of the surrounding waters, if it is lower than the current are called cold. In the same way, saline and desalinated currents are determined.

Warm and cold currents . These currents can be divided into two classes. The first class includes currents, the water temperature of which corresponds to the temperature of the surrounding water masses. Examples of such currents are the warm North and South trade winds and the cold current of the West Winds. The second class includes currents, the water temperature of which differs from the temperature of the surrounding water masses. Examples of currents of this class are the warm currents of the Gulf Stream and Kuroshio, which carry warm waters to higher latitudes, as well as the cold East Greenland and Labrador Currents, which carry cold waters of the Arctic Basin to lower latitudes.

Cold currents belonging to the second class, depending on the origin of the cold waters they carry, can be divided: into currents carrying the cold waters of the polar regions to lower latitudes, such as East Greenland, Labrador. the Falklands and Kurils, and lower latitude currents such as the Peruvian and Canary (the low temperature of the waters of these currents is caused by the rise of cold deep waters to the surface; but deep waters are not as cold as the waters of currents going from higher latitudes to low latitudes).

Warm currents carrying warm water masses to higher latitudes act on the western side of the main closed circulations in both hemispheres, while cold currents act on their eastern side.

On the eastern side of the southern Indian Ocean, there is no upwelling of deep waters. The currents on the western side of the oceans, compared with the surrounding waters at the same latitudes, are relatively warmer in winter than in summer. Cold currents coming from higher latitudes are of particular importance for navigation, as they carry ice to lower latitudes and cause in some areas a greater frequency of fog and poor visibility.

In the oceans by nature and speed the following groups can be distinguished. The main characteristics of the sea current: speed and direction. The latter is determined in the reverse way compared to the direction of the wind, i.e. in the case of the current, where the water flows, while in the case of the wind, where it blows from. Vertical movements of water masses are usually not taken into account when studying sea currents, since they are not large.

There is not a single area in the World Ocean where the speed of currents would not reach 1 knot. At a speed of 2–3 knots, there are mainly trade winds and warm currents near the eastern coasts of the continents. With such a speed there is an Intertrade countercurrent, currents in the northern part of the Indian Ocean, in the East China and South China Seas.

This I know

2. What are the reasons for the formation of currents?

The main reason for the formation of currents is the wind. In addition, the movement of water is affected by the difference in its temperature, density, salinity.

3. What is the role of ocean currents?

Ocean currents influence climate formation. Currents redistribute heat on the Earth. Due to the currents, planktonic organisms carry out their movements.

4. What are the types of ocean currents and give examples of them?

Currents by origin are windy (the course of Western winds), tidal, density.

Temperature currents are warm (Gulf Stream) and cold (Bengal).

Currents in terms of stability are permanent (Peruvian) and seasonal (currents of the northern part of the Indian Ocean, El Niña)

5. Match the current - warm (cold):

1) the course of the Western winds

2) Gulf Stream

3) Peruvian

4) Californian

5) Kuroshio

6) Benguela

A) warm

B) cold

This I can

6. Give examples of the interaction of the ocean and the atmosphere.

Currents redistribute heat and influence air temperature and precipitation. Sometimes the interaction of currents and the atmosphere leads to the formation of adverse and dangerous weather phenomena.

7. Give a description of the course of the Western winds according to the plan:

1. Geographic location

The current bends between 400 and 500 S. Earth.

2. Type of flow

A) according to the properties of water (cold, warm)

The current is cold.

B) by origin

The course of the Western winds is windy in origin. It is caused by westerly winds in temperate latitudes.

C) stability (permanent, seasonal)

The flow is constant.

D) by location in the water column (surface, deep, bottom)

Surface flow.

8. In ancient times, not knowing the real reasons for the formation of currents in the Ocean, sailors believed that Neptune, the Roman god of the seas, could drag a ship into the ocean depths. Using information from popular science and fiction literature, the Internet, collect materials about ships whose disappearance is associated with currents. Document the materials in the form of drawings, essays, reports.

Secrets of the Bermuda Triangle

The Bermuda Triangle or Atlantis is a place where people disappear, ships and planes disappear, navigation instruments fail, and almost no one ever finds the crashed. This hostile, mystical, ominous country for a person instills such great horror in the hearts of people that they often simply refuse to talk about it.

About the existence of such a mysterious and amazing phenomenon called the Bermuda Triangle a hundred years ago, few people knew. To actively occupy people's minds and force them to put forward various hypotheses and theories, this mystery of the Bermuda Triangle began in the 70s. of the last century, when Charles Berlitz published a book in which he described the stories of the most mysterious and mystical disappearances in this region in an extremely interesting and fascinating way. After that, the journalists picked up the story, developed the theme, and the story of the Bermuda Triangle began. Everyone began to worry about the secrets of the Bermuda Triangle and the place where the Bermuda Triangle or the missing Atlantis is located.

This wonderful place or the missing Atlantis is located in the Atlantic Ocean off the coast of North America - between Puerto Rico, Miami and Bermuda. It is located in two climatic zones at once: the upper part, the larger one - in the subtropics, the lower one - in the tropics. If these points are connected with each other by three lines, a large triangular figure will appear on the map, the total area of \u200b\u200bwhich is about 4 million square kilometers. This triangle is rather conditional, since ships also disappear outside its borders - and if you mark on the map all the coordinates of disappearances, flying and floating vehicles, you will most likely get a rhombus.

For knowledgeable people, the fact that ships often crash here is not particularly surprising: this region is not easy to navigate - there are many shoals, a huge number of fast water and air currents, cyclones often arise and hurricanes rage.

Water currents. Gulfstream.

Almost the entire western part of the Bermuda Triangle is crossed by the Gulf Stream, so the air temperature here is usually 10 ° C higher than in the rest of this mysterious anomaly. Because of this, in the places of collisions of atmospheric fronts of different temperatures, one can often see fog, which often strikes the mind of overly impressionable travelers. The Gulf Stream itself is a very fast current, the speed of which often reaches ten kilometers per hour (it should be noted that many modern transoceanic ships move slightly faster - from 13 to 30 km / h). An extremely fast flow of water can easily slow down or increase the movement of the ship (it all depends on which direction it is sailing). There is nothing surprising in the fact that ships of weaker power in the old days easily went off course and were swept absolutely in the wrong direction, as a result of which they suffered wrecks and disappeared forever in the oceanic abyss.

In addition to the Gulf Stream, strong but irregular currents constantly arise in the Bermuda Triangle, the appearance or direction of which is almost never predictable. They are formed mainly under the influence of tidal and ebb waves in shallow water and their speed is as high as that of the Gulf Stream - and is about 10 km / h. As a result of their occurrence, whirlpools are often formed, causing trouble for small ships with a weak engine. There is nothing surprising in the fact that if in former times a sailing ship got here, it was not easy for him to get out of the whirlwind, and under especially unfavorable circumstances, one might even say - impossible.

In the east of the Bermuda Triangle, the Sargasso Sea is located - a sea without shores, surrounded on all sides instead of land by the strong currents of the Atlantic Ocean - the Gulf Stream, the North Atlantic, the North Trade Wind and the Canary.

Outwardly, it seems that its waters are motionless, the currents are weak and hardly noticeable, while the water here is constantly moving, since the water flows, pouring into it from all sides, rotate the sea water clockwise. Another remarkable thing about the Sargasso Sea is the huge amount of algae in it (contrary to popular belief, there are also areas with completely clear water). When in former times ships were brought here for some reason, they became entangled in dense marine plants and, falling into a whirlpool, albeit slowly, they were no longer able to get back.

Marine (oceanic) or simply currents are the translational movements of water masses in the oceans and seas over distances measured in hundreds and thousands of kilometers, due to various forces (gravitational, friction, tide-forming).

There are several classifications of sea currents in the oceanological scientific literature. According to one of them, currents can be classified according to the following criteria (Fig. 1.1.):

1. according to the forces that cause them, that is, according to their origin (genetic classification);

2. stability (variability);

3. by location depth;

4. by the nature of the movement;

5. according to physical and chemical properties.

The main one is the genetic classification, in which three groups of currents are distinguished.

1. In the first group of genetic classification - gradient currents due to horizontal hydrostatic pressure gradients. There are the following gradient currents:

Density, due to the horizontal density gradient (uneven distribution of water temperature and salinity, and, consequently, density horizontally);

compensation, due to the slope of the sea level, which arose under the influence of the wind;

Barogradient, due to uneven atmospheric pressure above sea level;

· runoff, formed as a result of an excess of water in any area of the sea, as a result of the inflow of river water, heavy precipitation or melting ice;

· seiche, arising from seiche vibrations of the sea (fluctuations in the water of the entire basin as a whole).

Currents that exist when the horizontal gradient of hydrostatic pressure and the Coriolis force are in equilibrium are called geostrophic.

The second group of gradient classification includes currents caused by the action of the wind. They are divided into:

Drift winds are created by prolonged, or prevailing, winds. These include the trade winds of all oceans and the circumpolar current in the southern hemisphere (the current of the West Winds);

wind, caused not only by the action of the direction of the wind, but also by the slope of the level surface and the redistribution of water density caused by the wind.

The third group of classification gradients includes tidal currents caused by tidal phenomena. These currents are most noticeable near the coast, in shallow waters, in the mouths of rivers. They are the strongest.

As a rule, total currents are observed in the oceans and seas, due to the combined action of several forces. Currents that exist after the cessation of the action of the forces that caused the movement of water are called inertial. Under the action of friction forces, inertial flows gradually fade.

2. According to the nature of stability, variability, currents are distinguished as periodic and non-periodic (stable and unstable). Currents, changes of which occur with a certain period, are called periodic. These include tidal currents that vary mainly with a period of approximately half a day (semidiurnal tidal currents) or days (diurnal tidal currents).

Rice. 1.1. Classification of currents of the oceans

Currents whose changes do not have a clear periodic character are usually called non-periodic. They owe their origin to random, unexpected causes (for example, the passage of a cyclone over the sea causes non-periodic wind and barometric currents).

There are no permanent currents in the strict sense of the word in the oceans and seas. Relatively little changing currents in direction and speed for the season are monsoon, for the year - trade winds. A flow that does not change with time is called steady flow, and a flow that changes with time is called unsteady flow.

3. According to the depth of location, surface, deep and near-bottom currents are distinguished. Surface currents are observed in the so-called navigation layer (from the surface to 10–15 m), near-bottom currents are at the bottom, and deep ones are between the surface and near-bottom currents. The speed of movement of surface currents is highest in the uppermost layer. Deeper it goes down. Deep waters move much more slowly, and the speed of movement of bottom waters is 3–5 cm/s. The speed of the currents is not the same in different regions of the ocean.

4. According to the nature of the movement, meandering, rectilinear, cyclonic and anticyclonic currents are distinguished. Meandering currents are called currents that do not move in a straight line, but form horizontal undulating bends - meanders. Due to the instability of the flow, meanders can separate from the flow and form independently existing eddies. Rectilinear currents are characterized by the movement of water in relatively straight lines. Circular currents form closed circles. If the movement in them is directed counterclockwise, then these are cyclonic currents, and if clockwise, then they are anticyclonic (for the northern hemisphere).

5. According to the nature of the physicochemical properties, warm, cold, neutral, saline and fresh water currents are distinguished (the division of currents according to these properties is to a certain extent conditional). To assess the specified characteristic of the current, its temperature (salinity) is compared with the temperature (salinity) of the surrounding waters. Thus, a warm (cold) flow is a water temperature in which the temperature of the surrounding waters is higher (lower). For example, the deep current of Atlantic origin in the Arctic Ocean has a temperature of about 2 °C, but belongs to warm currents, and the Peruvian current off the western coast of South America, which has a water temperature of about 22 °C, belongs to cold currents.

The main characteristics of the sea current: speed and direction. The latter is determined in the reverse way compared to the direction of the wind, i.e., in the case of a current, it indicates where the water flows, while in the case of a wind, it indicates where it blows from. Vertical movements of water masses are usually not taken into account when studying sea currents, since they are not large.

In the oceans there is a single, interconnected system of main stable currents (Fig. 1.2.), which determines the transfer and interaction of waters. This system is called oceanic circulation.

The main force that drives the surface waters of the ocean is the wind. Therefore, surface currents should be considered with prevailing winds.

Within the southern periphery of the oceanic anticyclones of the northern hemisphere and the northern periphery of the southern hemisphere anticyclones (the centers of anticyclones are located at 30 - 35 ° north and south latitude), a system of trade winds operates, under the influence of which stable powerful surface currents are formed, directed to the west (North and South trade winds). currents). Encountering the eastern shores of the continents on their way, these currents create a rise in level and turn to high latitudes (Guiana, Brazil, etc.). In temperate latitudes (about 40°) westerly winds predominate, which intensifies currents going to the east (North Atlantic, North Pacific, etc.). In the eastern parts of the oceans between 40 and 20 ° north and south latitude, the currents are directed towards the equator (Canary, California, Benguela, Peru, etc.).

Thus, stable water circulation systems are formed in the oceans to the north and south of the equator, which are giant anticyclonic gyres. Thus, in the Atlantic Ocean, the northern anticyclonic gyre extends from south to north from 5 to 50° north latitude and from east to west from 8 to 80° west longitude. The center of this cycle is shifted relative to the center of the Azores anticyclone to the west, which is explained by the increase in the Coriolis force with latitude. This leads to the intensification of currents in the western parts of the oceans, creating conditions for the formation of such powerful currents as the Gulf Stream in the Atlantic and Kuroshio in the Pacific Ocean.

A peculiar division between the North and South trade winds is the Intertrade countercurrent, which carries its waters to the east.

In the northern part of the Indian Ocean, the Hindustan peninsula, which protrudes deeply to the south, and the vast Asian continent create favorable conditions for the development of monsoon circulation. In November - March, the northeast monsoon is observed here, and in May - September - southwest. In this regard, currents north of 8° south latitude have a seasonal course, following the seasonal course of atmospheric circulation. In winter, the western monsoon current is observed at the equator and north of it, i.e., during this season, the direction of surface currents in the northern part of the Indian Ocean corresponds to the direction of currents in other oceans. At the same time, in the zone separating the monsoon and trade winds (3 - 8 ° south latitude), a surface equatorial countercurrent develops. In summer, the western monsoon current is replaced by an eastern one, and the equatorial countercurrent is replaced by weak and unstable currents.

Rice. 1.2.

In temperate latitudes (45 - 65 °) in the northern part of the Atlantic and Pacific oceans, counterclockwise circulation takes place. However, due to the instability of the atmospheric circulation in these latitudes, the currents are also characterized by low stability. In the band 40 - 50 ° south latitude is the Atlantic circumpolar current directed to the east, also called the current of the West Winds.

Off the coast of Antarctica, the currents are predominantly westward and form a narrow strip of coastal circulation along the shores of the mainland.

The North Atlantic Current penetrates into the Arctic Ocean basin in the form of branches of the Norwegian, North Cape and Svalbard currents. In the Arctic Ocean, surface currents are directed from the shores of Asia across the pole to the eastern shores of Greenland. This nature of the currents is caused by the predominance of easterly winds and the compensation of the inflow in the deep layers of the Atlantic waters.

In the ocean, zones of divergence and convergence are distinguished, characterized by the divergence and convergence of surface jets of currents. In the first case, the water rises; in the second, it sinks. Of these zones, convergence zones are more clearly distinguished (for example, the Antarctic convergence at 50 - 60 ° south latitude).

Let us consider the features of the circulation of the waters of individual oceans and the characteristics of the main currents of the World Ocean (table).

In the northern and southern parts of the Atlantic Ocean, in the surface layer, there are closed circulations of currents with centers near 30 ° north and south latitude. (The circulation in the northern part of the ocean will be discussed in the next chapter).

The main currents of the oceans

Name	Temperature gradation	Sustainability	Average speed, cm/s

northern trade wind	Neutral	sustainable
Mindanao	Neutral	sustainable
		Very stable
North Pacific	Neutral	sustainable
		sustainable
Aleutian	Neutral	unstable
Kuril-Kamchatskoe	Cold	sustainable
california	Cold	unstable
Intertrade countercurrent	Neutral	sustainable
southern trade wind	Neutral	sustainable
East Australian		sustainable
South Pacific	Neutral	unstable
Peruvian	Cold	Weakly stable
El Niño		Weakly stable
Antarctic circumpolar	Neutral	sustainable
Indian
southern trade wind	Neutral	sustainable
Cape Agulhas		Very stable
Western Australian	Cold	unstable
Antarctic circumpolar	Neutral	sustainable
Northern	arctic
Norwegian		sustainable
West Spitsbergen		sustainable
East Greenland	Cold	sustainable
West Greenland		sustainable
Atlantic
northern trade wind	Neutral	sustainable
Gulfstream		Very stable
North Atlantic		Very stable
Canarian	Cold	sustainable
Irminger		sustainable
Labrador	Cold	sustainable
Intertrade countercurrent	Neutral	sustainable
southern trade wind	Neutral	sustainable
brazilian		sustainable
Benguela	Cold	sustainable
Falkland	Cold	sustainable
Antarctic circumpolar	Neutral	sustainable

In the southern part of the ocean, the warm Brazilian current carries water (at a speed of up to 0.5 m/s) far to the south, and the Benguela current, branched off from the powerful current of the West Winds, closes the main circulation in the southern part of the Atlantic Ocean and brings cold water to the coast of Africa.

The cold waters of the Falkland Current penetrate the Atlantic, rounding Cape Horn and pouring between the shore and the Brazil Current.

A feature in the circulation of the waters of the surface layer of the Atlantic Ocean is the presence of the Lomonosov subsurface equatorial countercurrent, which moves along the equator from west to east under a relatively thin layer of the South trade wind current (depth from 50 to 300 m) at a speed of up to 1 - 1.5 m/s. The current is stable in direction and exists in all seasons of the year.

Geographical position, climatic features, water circulation systems and good water exchange with Antarctic waters determine the hydrological conditions of the Indian Ocean.

In the northern part of the Indian Ocean, unlike other oceans, the monsoonal circulation of the atmosphere causes a seasonal change in surface currents north of 8 ° south latitude. In winter, the Western Monsoon Current is observed at a speed of 1 - 1.5 m/s. In this season, the Equatorial countercurrent develops (in the zone of separation of the Monsoon and South trade winds) and disappears.

Compared to other oceans in the Indian Ocean, the zone of prevailing southeast winds, under the influence of which the South Trade Wind Current arises, is shifted to the south, so this current moves from east to west (speed 0.5 - 0.8 m / s) between 10 and 20° south latitude. Off the coast of Madagascar, the South Tradewind current splits. One of its branches runs north along the coast of Africa to the equator, where it turns east and in winter gives rise to the Equatorial Countercurrent. In summer, the northern branch of the South Trade Wind Current, moving along the coast of Africa, gives rise to the Somali Current. Another branch of the South Trade Wind Current off the coast of Africa turns south and, under the name of the Mozambique Current, moves along the coast of Africa to the southwest, where its branch gives rise to the Cape of Needles Current. Most of the Mozambique Current turns east and joins the West Wind Current, from which the West Australian Current branches off off the coast of Australia, completing the circulation of the southern Indian Ocean.

The insignificant inflow of Arctic and Antarctic cold waters, the geographic position and the system of currents determine the features of the hydrological regime of the Pacific Ocean.

A characteristic feature of the general scheme of the surface currents of the Pacific Ocean is the presence of large water cycles in its northern and southern parts.

In the trade winds, under the influence of constant winds, the South and North trade winds arise, going from east to west. Between them, from west to east, the Equatorial (Intertrade) countercurrents move with speeds of 0.5 - 1 m / s.

The northern trade wind current near the Philippine Islands is divided into several branches. One of them turns south, then east and gives rise to the Equatorial (Intertrade) countercurrent. The main branch follows north along the island of Taiwan (Taiwan Current), then turns to the northeast and under the name Kuroshio runs along the eastern coast of Japan (speed up to 1 - 1.5 m / s) to Cape Nojima (Honshu Island). Further, it deviates to the east and crosses the ocean as the North Pacific Current. A characteristic feature of the Kuroshio Current, like the Gulf Stream, is meandering and displacement of its axis either to the south or to the north. Off the coast of North America, the North Pacific Current bifurcates into the California Current, which is directed to the south and closes the main cyclonic circulation of the North Pacific Ocean, and the Alaska Current, which goes to the north.

The cold Kamchatka Current originates in the Bering Sea and flows along the coasts of Kamchatka, the Kuril Islands (Kuril Current), and the coast of Japan, pushing the Kuroshio Current to the east.

The southern trade wind current moves to the west (velocity 0.5 - 0.8 m/s) with numerous branches. Off the coast of New Guinea, part of the flow turns north and then east and, together with the southern branch of the North Trade Wind Current, gives rise to the Equatorial (Intertrade) countercurrent. Most of the South Trade Wind Current is deflected, forming the East Australian Current, which then flows into the powerful West Wind Current, from which the cold Peruvian Current branches off off the coast of South America, completing the circulation in the South Pacific Ocean.

In the summer period of the southern hemisphere, towards the Peruvian current from the Equatorial countercurrent, the warm El Niño current moves south to 1 - 2 ° south latitude, penetrating in some years to 14 - 15 ° south latitude. Such an intrusion of the warm waters of El Niño into the southern regions of the coast of Peru leads to catastrophic consequences due to an increase in the temperature of water and air (heavy showers, death of fish, epidemics).

A characteristic feature in the distribution of currents in the surface layer of the ocean is the presence of the Equatorial subsurface countercurrent - the Cromwell Current. It crosses the ocean along the equator from west to east at a depth of 30 to 300 m at a speed of up to 1.5 m/s. The current covers a strip with a width from 2° north latitude to 2° south latitude.

The most characteristic feature of the Arctic Ocean is that its surface is covered with floating ice throughout the year. The low temperature and salinity of the waters favor the formation of ice. Coastal waters are free of ice only in summer, for two to four months. In the central part of the Arctic, mainly heavy multi-year ice (pack ice) with a thickness of more than 2 - 3 m, covered with numerous hummocks, is observed. In addition to multi-year ice, there are one-year and two-year ice. A rather wide (tens and hundreds of meters) strip of fast ice forms along the Arctic shores in winter. There are no ices only in the area of the warm Norwegian, North Cape and Svalbard currents.

Under the influence of winds and currents, the ice in the Arctic Ocean is in constant motion.

Well-defined areas of cyclonic and anticyclonic water circulation are observed on the surface of the Arctic Ocean.

Under the influence of the polar baric maximum in the Pacific part of the Arctic Basin and the hollow of the Icelandic minimum, a general Transarctic current arises. It carries out the general movement of waters from east to west throughout the polar area. The Transarctic Current originates from the Bering Strait and goes to the Fram Strait (between Greenland and Svalbard). Its continuation is the East Greenland current. Between Alaska and Canada there is an extensive anticyclonic water cycle. The cold Baffin Current is formed mainly due to the removal of Arctic waters through the straits of the Canadian Arctic Archipelago. Its continuation is the Labrador Current.

The average speed of water movement is about 15 - 20 cm / s.

A cyclonic, very intense circulation occurs in the Norwegian and Greenland Seas in the Atlantic part of the Arctic Ocean.

Which moves with a certain cyclicity and frequency. Differs in a constancy of physical and chemical properties and a specific geographical location. It can be cold or warm, depending on belonging to the hemispheres. Each such flow is characterized by increased density and pressure. The flow rate of water masses is measured in sverdrupa, in a broader sense - in units of volume.

Varieties of currents

First of all, cyclically directed water flows are characterized by such features as stability, speed of movement, depth and width, chemical properties, acting forces, etc. Based on the international classification, flows are of three categories:

1. Gradient. Occur when exposed to isobaric layers of water. A gradient ocean current is a flow characterized by horizontal movements of the isopotential surfaces of the water area. According to their initial features, they are divided into density, baric, stock, compensation and seiche. As a result of the runoff flow, precipitation and ice melting are formed.

2. Wind. Determined by the slope of the sea level, the strength of the air flow and fluctuations in mass density. A subspecies is drifting. This is a flow of water caused purely by the action of the wind. Only the surface of the pool is exposed to oscillations.

3. Tidal. They appear most strongly in shallow water, in estuaries and near the coast.

A separate type of flow is inertial. It is caused by the action of several forces at once. According to the variability of movement, constant, periodic, monsoon and trade wind flows are distinguished. The last two are determined by direction and speed seasonally.

Causes of ocean currents

At the moment, the circulation of waters in the world's waters is only beginning to be studied in detail. By and large, specific information is known only about surface and shallow currents. The main snag is that the oceanographic system has no clear boundaries and is in constant motion. It is a complex network of flows due to various physical and chemical factors.

Nevertheless, the following causes of ocean currents are known today:

1. Cosmic impact. This is the most interesting and at the same time difficult to learn process. In this case, the flow is determined by the rotation of the Earth, the impact on the atmosphere and hydrological system of the planet of cosmic bodies, etc. A striking example is the tides.

2. Wind exposure. The circulation of water depends on the strength and direction of air masses. In rare cases, we can talk about deep currents.

3. Density difference. Streams are formed due to uneven distribution of salinity and temperature of water masses.

atmospheric effect

In the world's waters, this kind of influence is caused by the pressure of heterogeneous masses. Coupled with cosmic anomalies, water flows in the oceans and smaller basins change not only their direction, but also their power. This is especially noticeable in the seas and straits. A prime example is the Gulf Stream. At the beginning of his journey, he is characterized by increased speed.

During the Gulf Stream, it is accelerated simultaneously by opposite and fair winds. This phenomenon forms a cyclic pressure on the layers of the pool, accelerating the flow. From here, in a certain period of time, there is a significant outflow and inflow of a large amount of water. The lower the atmospheric pressure, the higher the tide.

When the water level drops, the slope of the Florida Strait becomes less. Because of this, the flow rate is significantly reduced. Thus, it can be concluded that increased pressure reduces the force of the flow.

wind impact

The connection between the flows of air and water is so strong and at the same time simple that it is hard not to notice even with the naked eye. Since ancient times, navigators have been able to calculate the appropriate ocean current. This became possible thanks to the work of the scientist W. Franklin on the Gulf Stream, dating back to the 18th century. A few decades later, A. Humboldt indicated precisely the wind in the list of the main extraneous forces affecting the water masses.

From a mathematical point of view, the theory was substantiated by the physicist Zeppritz in 1878. He proved that in the World Ocean there is a constant transfer of the surface layer of water to deeper levels. In this case, the wind becomes the main influencing force on the movement. The current velocity in this case decreases in proportion to the depth. The determining condition for the constant circulation of waters is an infinitely long time of action of the wind. The only exceptions are the trade winds of air, which cause the movement of water masses in the equatorial strip of the World Ocean seasonally.

Density difference

The impact of this factor on water circulation is the most important cause of currents in the World Ocean. Large-scale studies of the theory were carried out by the international expedition Challenger. Subsequently, the work of scientists was confirmed by Scandinavian physicists.

The heterogeneity of the densities of water masses is the result of several factors at once. They have always existed in nature, representing a continuous hydrological system of the planet. Any deviation in water temperature entails a change in its density. In this case, an inversely proportional relationship is always observed. The higher the temperature, the lower the density.

Also, the state of aggregation of water affects the difference in physical indicators. Freezing or evaporation increases density, precipitation decreases it. Affects the strength of the current and salinity of water masses. It depends on the melting of ice, precipitation and the level of evaporation. In terms of density, the World Ocean is quite uneven. This applies to both surface and deep layers of the water area.

Currents of the Pacific Ocean

The general scheme of flows is determined by the circulation of the atmosphere. Thus, the east trade wind contributes to the formation of the North Current. It crosses the waters from the Philippine Islands to the coast of Central America. It has two branches that feed the Indonesian Basin and the Equatorial Ocean Current of the Pacific Ocean.

The largest currents in the water area are the Kuroshio, Alaska and California currents. The first two are warm. The third stream is the cold ocean current of the Pacific Ocean. The basin of the Southern Hemisphere is formed by the Australian and Tradewind currents. A little to the east of the center of the water area, the Equatorial countercurrent is observed. Off the coast of South America, there is a branch of the cold Peruvian current.

During the summer, the El Niño ocean current operates near the equator. It pushes back the cold masses of water of the Peruvian Stream, forming a favorable climate.

Indian Ocean and its currents

The northern part of the basin is characterized by a seasonal change of warm and cold flows. This constant dynamics is caused by the action of the monsoon circulation.

In winter, the Southwest Current dominates, which originates in the Bay of Bengal. A little further south is Western. This ocean current of the Indian Ocean crosses the water area from the coast of Africa to the Nicobar Islands.

In summer, the east monsoon contributes to a significant change in surface waters. The equatorial countercurrent shifts to a depth and noticeably loses its strength. As a result, its place is occupied by powerful warm Somali and Madagascar currents.

Arctic ocean circulation

The main reason for the development of the undercurrent in this part of the World Ocean is a powerful influx of water masses from the Atlantic. The fact is that the centuries-old ice cover does not allow the atmosphere and cosmic bodies to influence the internal circulation.

The most important course of the Arctic Ocean is the North Atlantic. It drives huge volumes of warm masses, preventing the water temperature from dropping to critical levels.

The Transarctic current is responsible for the direction of ice drift. Other major streams include the Yamal, Svalbard, North Cape and Norwegian currents, as well as a branch of the Gulf Stream.

currents of the atlantic basin

The salinity of the ocean is extremely high. The zonality of water circulation is the weakest among other basins.

Here the main ocean current is the Gulf Stream. Thanks to him, the average water temperature is kept at around +17 degrees. This warm ocean warms both hemispheres.

Also the most important streams of the basin are the Canary, Brazilian, Benguela and Tradewind currents.

4. Ocean currents.

The constant and continuous movement of water masses is the eternal dynamic state of the ocean. If the rivers on Earth flow towards the sea along their inclined channels under the influence of the force of gravity, then the currents in the ocean are caused by various reasons. The main causes of sea currents are: wind (drift currents), unevenness or changes in atmospheric pressure (barogradient), attraction of water masses by the Sun and Moon (tidal), difference in water density (due to the difference in salinity and temperature), level difference created by inflow of river water from the continents (stock).

Not every movement of ocean water can be called a current. Sea currents in oceanography are the translational movement of water masses in the oceans and seas..

Two physical forces cause currents - friction and gravity. Excited by these forces currents called frictional and gravitational.

The current in the World Ocean is usually caused by several reasons at once. For example, the mighty Gulf Stream is formed by the confluence of density, wind and runoff currents.

The initial direction of any current soon changes under the influence of the Earth's rotation, frictional forces, the configuration of the coastline and the bottom.

According to the degree of stability, currents are distinguished sustainable(for example, the North and South trade winds), temporary(surface currents of the northern Indian Ocean caused by monsoons) and periodical(tidal).

According to the position in the thickness of the ocean waters, the currents can be surface, subsurface, intermediate, deep and bottom. In this case, the definition of "surface current" sometimes refers to a sufficiently powerful layer of water. For example, the thickness of the trade wind countercurrents in the equatorial latitudes of the oceans can be 300 m, and the thickness of the Somali current in the northwestern part of the Indian Ocean reaches 1000 meters. It is noted that deep currents are most often directed in the opposite direction compared to surface waters moving above them.

Currents are also divided into warm and cold. warm currents move water masses from low latitudes to higher latitudes, and cold- in the opposite direction. This division of currents is relative: it characterizes only the surface temperature of moving waters in comparison with the surrounding water masses. For example, in the warm North Cape Current (Barents Sea), the temperature of the surface layers is 2–5 °С in winter and 5–8 °С in summer, and in the cold Peruvian Current (Pacific Ocean) it is 15 to 20 °С all year round, in the cold Canary (Atlantic) - from 12 to 26 ° С.

The main data source is ARGO buoys. The fields are obtained using optimal analysis.

Some currents in the oceans are connected with other currents, forming a basin-wide circulation.

In general, the constant movement of water masses in the oceans is a complex system of cold and warm currents and countercurrents, both surface and deep.

The most famous for the inhabitants of America and Europe is, of course, the Gulf Stream. Translated from English, this name means Current from the Gulf. Previously, it was believed that this current begins in the Gulf of Mexico, from where it rushes through the Strait of Florida to the Atlantic. Then it turned out that the Gulf Stream takes out only a small fraction of its flow from this bay. Having reached the latitude of Cape Hatteras on the Atlantic coast of the United States, the current receives a powerful influx of water from the Sargasso Sea. This is where the actual Gulf Stream begins. A feature of the Gulf Stream is that when it enters the ocean, this current deviates to the left, while under the influence of the Earth's rotation it should deviate to the right.

The parameters of this mighty current are very impressive. The surface speed of water in the Gulf Stream reaches 2.0–2.6 meters per second. Even at a depth of up to 2 km, the speed of water layers is 10–20 cm/s. When leaving the Strait of Florida, the current carries 25 million cubic meters of water per second, which is 20 times more than the total flow of all the rivers of our planet. But after joining the flow of water from the Sargasso Sea (Antilles current), the capacity of the Gulf Stream already reaches 106 million cubic meters of water per second. This powerful stream moves northeast to the Great Newfoundland Bank, and from here it turns south and, together with the Slope Current separated from it, is included in the North Atlantic water cycle. The depth of the Gulf Stream is 700–800 meters, and the width reaches 110–120 km. The average temperature of the surface layers of the current is 25–26 °С, and at depths of about 400 m it is only 10–12 °С. Therefore, the idea of the Gulf Stream as a warm current is created precisely by the surface layers of this stream.

Note another current in the Atlantic - the North Atlantic. It runs across the ocean to the east, towards Europe. The North Atlantic Current is less powerful than the Gulf Stream. The water flow here is from 20 to 40 million cubic meters per second, and the speed is from 0.5 to 1.8 km/h, depending on the location. However, the influence of the North Atlantic Current on the climate of Europe is very noticeable. Together with the Gulf Stream and other currents (Norwegian, North Cape, Murmansk), the North Atlantic Current softens the climate of Europe and the temperature regime of the seas washing it. Only one warm current, the Gulf Stream, cannot have such an impact on the climate of Europe: after all, the existence of this current ends thousands of kilometers from the coast of Europe.

Now back to the equatorial zone. Here the air heats up much stronger than in other parts of the world. The heated air rises, reaches the upper layers of the troposphere and begins to spread towards the poles. Approximately in the region of 28-30 ° northern and southern latitudes, having cooled, the air begins to descend. Increasingly new air masses flowing in from the equator create excess pressure in subtropical latitudes, while over the equator itself, due to the outflow of heated air masses, the pressure is constantly lowered. From areas of high pressure, air rushes to areas of low pressure, that is, to the equator. The rotation of the Earth around its axis deflects the air from the direct meridional direction to the west. So there are two powerful streams of warm air, called trade winds. In the tropics of the Northern Hemisphere, the trade winds blow from the northeast, and in the tropics of the Southern Hemisphere, from the southeast.

For simplicity of presentation, we do not mention the influence of cyclones and anticyclones in the temperate latitudes of both hemispheres. It is important to emphasize that the trade winds are the most stable winds on Earth, they blow constantly and cause warm equatorial currents that move huge masses of ocean water from east to west.

Equatorial currents are useful in navigation, helping ships to quickly cross the ocean from east to west. At one time, H. Columbus, not knowing anything in advance about the trade winds and equatorial currents, felt their powerful effect during his sea voyages.

Based on the constancy of equatorial currents, the Norwegian ethnographer and archaeologist Thor Heyerdahl put forward a theory about the initial settlement of the islands of Polynesia by the ancient inhabitants of South America. To prove the possibility of sailing on primitive ships, he built a raft, which, in his opinion, was similar to those that the ancient inhabitants of South America could use when crossing the Pacific Ocean. On this raft, called "Kon-tiki", Heyerdahl, along with five other daredevils, made a dangerous voyage from the coast of Peru to the Tuamotu archipelago in Polynesia in 1947. For 101 days, he swam a distance of about 8 thousand kilometers along one of the branches of the southern equatorial current. The daredevils underestimated the power of the wind and waves and almost paid for it with their lives. Nearby, the warm equatorial current, driven by the trade winds, is not at all gentle, as one might think.

Let us briefly dwell on the characteristics of other currents in the Pacific Ocean. Part of the waters of the northern equatorial current in the Philippine Islands turns north, forming the warm current Kuroshio (Japanese for "Dark Water"), which is directed by a powerful stream past Taiwan and the southern Japanese islands to the northeast. The width of Kuroshio is about 170 km, and the depth of penetration reaches 700 m, but in general, this current is inferior to the Gulf Stream in fashion. About 36°N Kuroshio turns into the ocean, moving into the warm North Pacific Current. Its waters flow east, cross the ocean at about the 40th parallel, and warm the coast of North America all the way to Alaska.

The lapel of Kuroshio from the coast was noticeably affected by the influence of the cold Kuril current, approaching from the north. This current is called Oyashio (Blue Water) in Japanese.

Another remarkable current in the Pacific Ocean is El Niño (Spanish for "Baby"). This name is given because the El Niño current approaches the shores of Ecuador and Peru before Christmas, when the arrival of the baby Christ into the world is celebrated. This current does not occur every year, but when it nevertheless approaches the shores of the countries mentioned, it is not perceived otherwise than as a natural disaster. The fact is that too warm El Niño waters have a detrimental effect on plankton and fish fry. As a result, the catches of local fishermen are reduced tenfold.

Scientists believe that this treacherous current can also cause hurricanes, rainstorms and other natural disasters.

In the Indian Ocean, waters move along an equally complex system of warm currents, which are constantly influenced by monsoons - winds that blow from the ocean to the continent in summer, and in the opposite direction in winter.

In the band of the fortieth latitudes of the Southern Hemisphere in the World Ocean, winds constantly blow in the direction from west to east, which generates cold surface currents. The largest of these currents, where the waves are almost constantly raging, is the current of the West Winds, which circulates in the direction from west to east. The band of these latitudes from 40° to 50° on both sides of the equator is not accidentally called by sailors the “Roaring Forties”.

The Arctic Ocean is mostly covered in ice, but this did not make its waters at all motionless. The currents here are directly observed by scientists and specialists from drifting polar stations. For several months of drifting, the ice floe, on which the polar station is located, sometimes travels many hundreds of kilometers.

The largest cold current in the Arctic is the East Greenland Current, which carries the waters of the Arctic Ocean into the Atlantic.

In areas where warm and cold currents meet, phenomenon of deep water rise (upwelling), in which vertical flows of water carry deep water to the surface of the ocean. Together with them, nutrients rise, which are contained in the lower horizons of the water.

In the open ocean, upwelling occurs in areas where currents diverge. In such places, the ocean level drops and deep water inflow occurs. This process develops slowly - a few millimeters per minute. The most intense rise in deep waters is observed in coastal areas (10-30 km from the coastline). In the World Ocean, there are several permanent upwelling areas that affect the overall dynamics of the oceans and affect fishing conditions, for example: the Canary and Guinean upwellings in the Atlantic, the Peruvian and Californian upwellings in the Pacific Ocean, and the Beaufort Sea upwelling in the Arctic Ocean.

Deep currents and rises of deep waters are reflected in the nature of surface currents. Even such mighty currents as the Gulf Stream and Kuroshio, from time to time, either intensify or weaken. In them, the temperature of the water changes and deviations from the constant direction and huge swirls are formed. Such changes in sea currents affect the climate of the respective land regions, as well as the direction and distance of migration of some species of fish and other animal organisms.

Despite the apparent randomness and fragmentation of sea currents, in fact they represent a certain system. The currents provide them with the same salt composition and unite all the waters into a single World Ocean.