Currents are very important for navigation, affecting the speed and direction of the ship. Therefore, in navigation it is very important to be able to take them into account correctly (Fig. 18.6).
To choose the most profitable and safe routes when sailing near the coast and on the high seas, it is important to know the nature, direction and speed of sea currents.
When sailing by dead reckoning, sea currents can have a significant effect on its accuracy.
Sea currents - the movement of water masses in the sea or in the ocean from one place to another. The main causes that cause sea currents are wind, atmospheric pressure, tidal phenomena.
Sea currents are divided into the following types
1. Wind and drift currents arise under the influence of wind due to the friction of moving air masses on the sea surface. Prolonged, or prevailing, winds cause the movement of not only the upper, but also deeper layers of water, and form drift currents.
Moreover, drift currents caused by trade winds (constant winds) are constant, and drift currents caused by monsoons (variable winds) change both direction and speed during the year. Temporary, short-lived winds cause wind currents that are of a variable nature.
2. Tidal currents are caused by changes in sea level due to tides. In the open sea, tidal currents constantly change their direction: in the northern hemisphere - clockwise, in the southern - counterclockwise. In straits, narrow bays and along the coast, the currents are directed in one direction at high tide, and in the opposite direction at low tide.
3. Waste currents are caused by a rise in sea level in certain areas as a result of the inflow of fresh water from rivers, large amounts of precipitation, etc.
4. Density currents arise due to uneven distribution of water density in the horizontal direction.
5. Compensatory currents arise in a particular area to make up for the loss of water caused by its runoff or surge.
Rice. 18.6. Currents of the oceans
The Gulf Stream, the most powerful warm current in the World Ocean, runs along the shores of North America in the Atlantic Ocean, and then deviates from the coast and breaks up into a number of branches. The northern branch, or North Atlantic Current, runs to the northeast. The presence of the North Atlantic warm current explains the relatively mild winters on the coast of Northern Europe, as well as the existence of a number of ice-free ports.
In the Pacific Ocean, the North Trade Wind (Equatorial) Current begins off the coast of Central America, crosses the Pacific Ocean at an average speed of about 1 knot, and splits into several branches near the Philippine Islands.
The main branch of the North Trade Wind Current runs along the Philippine Islands and follows the northeast under the name Kuroshio, which is the second most powerful warm current of the World Ocean after the Gulf Stream; its speed is from 1 to 2 knots and even at times up to 3 knots.
Near the southern tip of Kyushu, this current splits into two branches, one of which, the Tsushima Current, heads to the Korea Strait.
The other, moving to the northeast, passes into the North Pacific Current, which crosses the ocean to the east. The cold Kuril Current (Oyashio) follows Kuroshio along the Kuril Ridge and meets it approximately at the latitude of the Sangar Strait.
The current of the westerly winds off the coast of South America is divided into two branches, one of which gives rise to the cold Peruvian current.
In the Indian Ocean, the southern trade wind (equatorial) current near the island of Madagascar is divided into two branches. One branch turns to the south and forms the Mozambique current, the speed of which is from 2 to 4 knots.
At the southern tip of Africa, the Mozambique Current gives rise to a warm, powerful and stable Needle Current, with an average speed of more than 2 knots and a maximum speed of about 4.5 knots.
In the Arctic Ocean, the bulk of the surface layer of water moves clockwise from east to west.
currents of the atlantic ocean
South trade wind. It starts almost from the coast of Africa with a strip of about 10 degrees of latitude. The northern limit of the current is about 1°N at the beginning and off the coast of South America it reaches 6-7° N. It is very stable, the maximum daily speed is 55 miles. In winter, the speed is less than in summer. It reaches Cape Cabo Branco, where it divides into the Brazilian Current, which goes south, and the Guiana Current.
Guiana current. From Cape Cabo Branco it is directed to the northwest along the coast of South America, the speed is 30-60 miles per day, the temperature is 27-28 °. In summer, its speed reaches 90 miles. Entering the Caribbean Sea, it flows from the straits between the Lesser Antilles to the Yucatan Strait across the entire surface of the Caribbean Sea. Speed up to 35-50 miles. Passing the Gulf of Mexico, it mostly deviates towards the Strait of Florida. Later it merges with the northern trade wind current.
North trade wind. It starts from Cape Verde with a strip between 8 and 23 ° N. Speed up to 20 miles. Approaching the Lesser Antilles, it gradually deviates to the west-north-west, dividing into two branches. The oceanic branch gets the name of the Antilles Current, the speed of which is 10-20 miles per day. In the future, the Antilles current joins the Gulf Stream. The second branch merges with the Guiana current, entering with it into the Caribbean Sea.
Gulfstream . Starts from Florida Strait. Speed up to 120 miles per day at the beginning and 40-50 at Cape Hatteras. It flows along the coast of North America from the Florida Strait to the eastern Newfoundland bank, where the current begins to branch. With distance to the north, the speed of the current drops from 45-50 miles per day to 25-30 miles. Among the current, which widens at 50° W to 350 miles, bands appear with different speeds and temperatures. Between the Gulf Stream and the coast of the mainland there is a strip of cold water, which is a continuation of the branch of the cold Labrador current from the Gulf of St. Lawrence. The eastern limit of the Gulf Stream should be considered the region of the eastern tip of Newfoundland, approximately 40 ° W.
North Atlantic Current. This name is given to the entire complex of currents of the North Atlantic Ocean. They begin from the northeastern border of the Gulf Stream, being its continuation. Between Newfoundland and the English Channel, the average current speed is 12-15 miles per day, and the southern border runs approximately 40 ° N. Gradually, the southeastern branch is separated from its southern edge, washing Azores, this branch is called the North African, or Canary Current. According to its water temperature, the currents are 2-3 ° colder than those around them. In the future, the Canary Current, turning to the southwest, gives rise to the Northern Trade Wind Current. The Atlantic current, approaching the shores of Europe, gradually turns to the northeast. At the parallel of Ireland, a branch called the Irminger Current separates from it to the left, going to the southern tip of Greenland, and further in the middle of the Davis Strait to the Baffin Sea, forming there the warm West Greenland Current. The main part of the Atlantic current passes through the straits between Iceland and Scotland to the edge of the mainland slope of Norway and along its coast to the north. After passing through Norway, the current splits into two branches, one branch goes eastward under the name of the North Cape current into the Barents Sea, and the second one goes to Svalbard, skirting the island along its western shores and gradually disappearing.
East Greenland Currentgoes from the northeast to Cape Farewell, and from this cape to the Davis Strait between the coast of Greenland and the warm West Greenland Current. In the Danish Strait, the speed of this current reaches 24 miles per day.
Labrador Currentoriginates from the straits of the North American archipelago, flowing along the western coast of the Baffin Sea. Its speed in this sea is somewhat less than 10 miles per day, but later increases to 14 miles. The waters of this current, meeting with the Gulf Stream, go under it; they carry icebergs from Greenland to the meeting area, which pose a significant danger to ships, especially since up to 43% of foggy days a year are observed in the meeting area of the currents. The West Greenland and East Greenland currents adjoin the Labrador Current in the Davis Strait and at Cape Farewell.
brazilian current. It is the southern branch of the Southern trade wind current, its speed is 15-20 miles per day. South of the river mouth Parana gradually moves away from the coast and turns to the east from 45 ° S, merging with the current of the Western winds, directed to the Cape of Good Hope.
Falkland Currentformed by the cold waters of the current of the Western winds, its branch going to the equator along the eastern coasts of Patagonia and South America. This current, reaching up to 40 ° S, brings with it a large number of ice mountains, mainly in the summer of the southern hemisphere (October-December). In the future, it adjoins the course of the Western winds.
benguela currentarises as the northern branch of the Western Winds current, departing from it at the Cape of Good Hope to the equator along the western coast of Africa. Speed about 20 miles per day. The current reaches 10°S and, turning there to the west, gives rise to the South Trade Wind Current.
Currents of the Indian Ocean
In the northern part of the ocean, drift currents are established under the influence of monsoon winds ranging from 10°S to the mainland of Asia. Since November, in the southern part of the Bay of Bengal, from the Strait of Malacca to Ceylon and south of it, the Monsoon current has been moving westward at a speed of 50-70 miles per day. The same picture is in the Arabian Sea, but the speed of the current does not exceed 10-20 miles. Approaching the coast of Africa, the current turns to the southwest, increasing the daily speed to 50-70 miles, here it is called Somali. Having crossed the equator and meeting with a branch of the Southern trade wind current, it turns to the east, forming the Equatorial Countercurrent, which crosses the ocean between 0-10 ° S at a speed of about. Sumatra up to 40-60 miles per day. In this region, the current partly goes north, but mostly turns south and joins the South Trade Wind Current. From May to October, the monsoon current stops. The southern trade wind current is divided into two branches. The northern branch runs along the coast of Somalia, somewhat intensifying after crossing the equator and reaching speeds from 40 to 120 miles per day. Then this branch turns to the east, reducing the speed to 25-50 miles, off the coast of Ceylon the speed increases to 70-80 miles. Approaching about. Sumatra turns south and joins the South Trade Winds. The currents of the Indian Ocean of the southern hemisphere form a constant circulation of water throughout the year.
South trade wind. Northern boundary -10°S, southern boundary poorly defined. In winter, the speed of the northern hemisphere is greater than in summer. Average speed 35 miles, maximum 50-60 miles. Occurs off the coast of Australia, and reaching about. Madagascar, is divided into two branches. The northern branch, reaching the northern tip of Madagascar, in turn is divided into two branches, one of which turns north, and in our winter, not reaching the equator and merging with the Monsoon current, forms the Equatorial countercurrent, and the second branch runs along the coast of Africa by the Mozambique the strait, forming a strong Mozambique current with an average speed of up to 40 miles and a maximum of 100 miles per day. Further, this current passes into the Igolnoye Current, which, south of 30 degrees S, has a flow up to 50 miles wide at a speed of up to 50 miles per day.
The course of the West winds. It is formed by cold waters flowing from the Atlantic Ocean at their confluence with the Needle Current, and the second main branch of the South Trade Wind Current, called the Madagascar Current. The speed of the Western winds is 15-25 miles per day. In Australia, a branch to the equator separates from it, called the West Australian Current, its speed is 15-30 miles, it is not very stable. At the tropic, the West Australian Current turns into the South Trade Wind.
Currents of the Pacific Ocean
North trade wind. Noticeable from the southern tip of California. Boundaries between 10 and 22° N. In northern hemisphere winter, the southern boundary is closer to the equator, and further away from it in summer. To the Philippine Islands, the average speed is 12-24 miles, in summer the speed is higher. From the Philippine Islands, it mainly deviates to about. Taiwan and, starting from here, gets the name of the Japanese current, or Kuro-Shiwo (blue current).
Kuro - Sivo . Off the island of Taiwan, it is about 100 miles wide, deviates to the right from the island, passes west of the Liu Kiu Islands to the Japanese Islands. At first, the speed of the current is 35-40 miles per day, near the Ryukyu Islands up to 70-80 miles, and in summer even up to 100 miles. Off the coast of Japan, the width of the current reaches 300 miles and the speed decreases. The Kuro-Sivo proper has its northern boundary at 35° N. The Kuro-Sivo current system includes the continuation of the Kuro-Sivo proper from 35° N. to the east, the western drift of the Kuro-Sivo, passing between 40 and 50° N at a speed of 10-20 miles to 160 ° E and its further continuation to the shores of North America - the North Pacific Current. The same system includes the southern branch of the North Trade Wind Current, passing from the Philippine Islands along the island of Mindanao, and the Tsushima Current, the Kuro-Sivo branch, passing in the Sea of Japan off the coast of the Japanese Islands to the north. The North Pacific Current reaches 170°W at a speed of 10-20 miles per day, where one branch deviates to the north, with some of the water even entering the Bering Sea, and the second branch, called the California Current, deviates to the south, where it has a speed of about 15 miles. Later, the California Current joins the North Trade Wind Current.
Kuril Current- a cold current flowing from the Kuril Islands along the western coast of Japan before meeting with the Kuro-Sivo going east.
equatorial countercurrent. In summer, the width is from 5 to 10 ° N, in winter 5-7 ° N. The speed in summer is about 30 miles, but sometimes it reaches 50-60 miles, in winter the speed is 10-12 miles. Approaching the shores of Central America, in winter this current divides into two branches, each adjoining the corresponding Equatorial Current, in summer it turns mainly to the north.
South trade wind goes west from the Galapagos Islands to the shores of Australia and New Guinea. In summer its northern border is 1 degree N, in winter -3°N. The speed of the current in its eastern half is at least 24 miles, and sometimes reaches 50-80 miles per day. North of New Guinea, part of the current turns east, joining the Equatorial Countercurrent. The second part from the coast of Australia turns to the south, forming the East Australian Current.
East Australian Currentstarts from the island of New Caledonia, goes south to the island of Tasmania, turns east there and washes the coast of New Zealand, forming a counterclockwise circulation of waters in the Tasman Sea. Current speed up to 24 miles per day. Part of the East Australian Current runs between Tasmania and the southern tip of New Zealand and then joins the West Wind Current from the Indian Ocean south of Australia.
The course of the West windsThe Pacific Ocean has a northern boundary of 40°S and flows east to Cape Horn at a speed of about 15 miles. Along the way, cold Antarctic waters join the current, carrying ice mountains and warm waters branching off from the South Trade Wind Current. Off the coast of South America, part of the current of the West Winds deviates to the south and passes further into the Atlantic Ocean, and the second part deviates to the equator along the western coasts of South America under the name of the Peruvian current.
Peruvian Currenthas a speed of 12-15 miles per day and goes up to 5 ° S, where, deviating to the east, washes the Galapagos Islands and then flows into the South trade wind current. Current width up to 500 miles.
Currents of the Arctic Ocean
The main mass of surface water, starting approximately from Prince Patrick Island (120 ° W), moves east to west along the northern coast of Alaska in a clockwise direction, dragging the surface fresh water of the marginal seas with it. Between 90 and 120 ° W, this current ceases to be continuous, approaching about. Ellesmere, it partly curves along the coast of Greenland into the Greenland Sea. Also, the current, directed from east to west and going north of the island of Svalbard, carries surface cold polar waters. Merging together in the north of the Greenland Sea, these currents form the cold East Greenland Current.
surface currentsthe central part of the Arctic arise mainly under the influence of air currents. The speed of the currents is insignificant - from 0.5 to 1 mile per day. At the pole, the current speed is somewhat higher, up to 1.4 miles, and at the outlet to the Greenland Sea it reaches 3.4 miles per day. From the south, along the shores of the Scandinavian Peninsula, the warm North Cape Current moves into the Arctic Ocean, enveloping about. Svalbard one branch and the second, passing to about. New Earth. Both branches of the current gradually fade and go to the depth.
tidal currentsare characterized by their periodicity in the change of speed and direction for a semi-diurnal or diurnal period. Characteristics of tidal currents are given in the relevant navigation manuals.
drift currentsin shallow seas they are established a few days after the beginning of the wind, in the open ocean after 3-1 months and in the area of constant winds they reach high power. In the open ocean, surface currents deviate approximately 45° from the direction of the wind, to the right of the wind in the northern hemisphere and to the left in the southern. In shallow water and near the coast, the deviation is very small, more often the direction of the wind coincides with the direction of the current.
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 direction of propagation by 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 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.
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.
The issues of flow typification were considered by many authors (B. D. Zaikov (1955), A. V. Karaushev (1969), B. B. Bogoslovsky (1960), D. Hutchinson (Hutchinson, 1957), B. Dussard (Dussart, 1954 , 1966). Most fully take into account the features of currents in an open reservoir and in the coastal zone of the typifications of B. D. Zaikov and A. V. Karausheva. However, these typifications do not reflect the specifics of their development in artificial reservoirs. According to the hydrologists of Perm State University, it is more acceptable for reservoirs typified by T. N. Filatova (1972).In accordance with this typification, the currents of inland water bodies are divided into two groups: currents observed throughout the water area (including in the coastal zone) and currents developing only in the coastal zone. first group include runoff, flow, wind, wave, density, barogradient, seiche, intrawave and inertial currents. To second group include alongshore wind, compensatory currents (Matarzin, Bogoslovsky, Matskevich, 1977).
stock currents arise as a result of the inclination of the water surface when the ratio of the main elements of the water balance changes - inflow into the reservoir and outflow from it.
wind currents caused by the shear stress of the wind. The types of wind currents are drift currents that have arisen directly as a result of the action of the wind on the surface of the water and the capture of water masses of the near-surface layer. wind gradient and secondary wind currents are observed at some depth and in the surface layer.
Wave (Stokes) flows- an integral part of the drift current - are determined by the translational movement of water that occurs during waves (simultaneously with the movement of particles in orbits). In its pure form, it is observed in swell waves.
Density(convective) currents arise as a result of an uneven distribution of water density, which is mainly due to a spatial change in its temperature and salinity. The uneven distribution of the water mass with density currents is restored compensatory flows.
Barogradient currents arise as a result of the skew of the water surface under the influence of sharp changes in atmospheric pressure and are of a compensatory nature. Barogradient currents are a type of seiche currents.
Seiche currents develop during seiche oscillations of the surface of reservoirs, which occur during the periodic effects of meteorological elements on the water surface of reservoirs (wind, pressure, as well as surge phenomena, with intense precipitation). During seiches, oscillatory movements of the entire water mass occur with a periodic change in slope.
intrawave currents develop during the formation of internal waves and are observed at the interface between waters of different densities.
Inertial currents take place after the termination of the force that caused the movement of the water mass. A special case of inertial flows are inertial spiral currents. Their direction is largely determined by the action of the Coriolis force.
The first group of flows also includes wave - sewer currents, the emergence and development of which is due to the uneven operation of hydraulic structures (hydroelectric power plants, locks, water intakes). These currents have a local development and are observed only in artificial reservoirs in the areas of operation of these hydraulic structures.
Among the currents of the first group, runoff (flowing) and wind currents have the greatest frequency and importance. On this basis, T.N. Filatova (1969) defines them as first order currents, and combines all other types of flows as flows second order.
currents second group develop exclusively in the coastal zone. They are characterized by a complex structure and their development is greatly influenced by the configuration of the coast and the bottom topography. Of greatest practical importance are coastal wind currents. They represent a kind of wind currents observed in open water. As a result of the transformation of wave energy with an oblique approach of waves to the shore, alongshore wave-surf currents are formed, which belong to the category of energy ones. A special case of wave-cutting are rip currents. Unlike the first ones, they occur during the normal approach of waves to the shore, as a result of the accumulation of water masses in the coastal zone. They compensate in the form of separate concentrated jets the inflow of water into the wave-surf zone and are always directed from the shore to the open part of the reservoir, often in the form of “tongues” saturated with sediment.
Some of the types of flows considered can be considered as compensatory currents. In essence, compensatory currents represent the movement of water that occurs at different hydrostatic pressures in certain parts of the reservoir and tends to restore its disturbed state.
In practice, currents of only one kind are rarely observed. As a rule, several types of currents develop and act simultaneously. As a result, in certain situations, systems of surface and deep currents are formed. In observational practice, such currents are called summary. Usually, in certain seasons, there is a predominance of certain types of total currents, which operate for a long period forming circulation schemes. With the simultaneous action of two main currents, they are called their combination (runoff-wind, density-wind, runoff-wave, etc.).
Total currents are currents with a complex structure. However, in reservoirs there is a different form of movement of water masses: rectilinear, reverse, circulation, circular, etc.
According to the stability or variability of the flow of artificial reservoirs are divided into permanent and temporary. Constant currents are observed throughout the reservoir or in its individual sections. In the case of stable maintenance of the general direction of the flow, it is referred to quasi-permanent, or quasi-stationary.
Most of the currents observed in reservoirs are temporary. In accordance with the variability of the main characteristics (direction and speed), all temporary currents are divided into non-periodic, periodic and flows with periodic change in one of the characteristics.
Non-periodic flows include currents that arise and change in the course of development, without a certain periodicity. This type of currents is observed mainly as a result of direct wind action. Non-periodic currents are those whose speed and direction change regularly after a certain period of time. The frequency of current changes can range from several hours and minutes to a season or a year.
An example of intermittent factors can be a regular decrease in discharge through a hydroelectric station at night and weekends, or annual spring floods. Periodic flows can also be formed by the non-periodic action of a force. Such currents include the movement of the water mass observed during seiches and internal waves.
In cases where the changes observed in the characteristics of the currents are short-term and do not have a definite regularity, they should be called quasi-periodic. Filatova T. N. (1970) classifies inertial spiral flows as temporal flows characterized by quasi-periodicity in direction.
By position (localization) currents are separated depending on their development in the water area of the reservoir (throughout the entire reservoir or only in the coastal zone) and in depth. The flows propagating on the surface with the capture of a small layer in depth are tosuperficial. Currents observed in the deep layers and not expressed on the surface are called g bast. Currents noted only in the immediate vicinity of the bottom of the reservoir are called bottom.
According to the nature and form of movement currents are divided into rectilinear and circulating, In the latter case, the movement of water masses occurs along closed circular or elliptical trajectories. Depending on the direction, there are cyclonic(counterclockwise movement) and anticyclonic circulation.-Depending on the plane of development of circulation, there are horizontal and vertical circulation.
According to the physicochemical properties, cold and warm currents are distinguished.
Among the considered types of currents, the most common are runoff and wind currents, or total, i.e. derivatives from them.
Sea currents - about the main thing. The headlines of newspapers and magazines, and sometimes even the plots of television programs, are full of and flicker with loud words that humanity has once again doomed itself to death, since one of the key ocean currents has made one of the key ocean currents disappear with its actions.
Despite the fact that many such statements have been made over the past decades, dramatic changes in climate for some reason are not observed.
There are people who believe that within a few months or years there will be an ice age. There are those who do not believe. But what if, before immediately drawing a conclusion about the justification of such bold statements, to understand the very phenomenon of ocean currents?
It may seem strange to some that the very fact that water on our planet does not stand still, but constantly travels. However, everything is quite simple here: in this way it is forced to behave by its own composition.
As a simple example, salt water is heavier than fresh water and the density varies with temperature. Add to this the fact that in different oceans the salinity of the liquid varies, and in different climatic zones the sun heats it up to varying degrees and at different rates.
The combination of all these factors form such phenomenal phenomena as sea currents.
The currents arising from the temperature and chemical characteristics of the World Ocean are called thermohaline. There are also those who owe their appearance to the geographical features of the seabed: in one place the depth is greater, in another less. However, the most significant factors influencing the appearance of currents are the Coriolis force and the wind.
Sea Currents Gulf Stream and the Coriolis Force
One of the currents that can be attributed to wind currents is the circulation of water, which is quite decent in terms of scale, occurring in the northern part of the Atlantic. There, on the surface of the ocean, all the water moves extremely slowly - only a few centimeters per second.
At first glance, nothing special: on the one hand (east) the water moves to the south, and on the other (west) to the north. But something else plays a key role here.
The Coriolis force is the inertial force resulting from the rotation of the Earth. It seems to “press” the current to the mainland, where a large amount of water moving at a low speed suddenly accelerates to 2 meters per second.
This current is called the western boundary current, and arises from a sharp collision with the mainland. Since the water has nowhere else to go, its pressure increases and, pushing itself out, it follows along the coast, after which it turns into the Gulf Stream.
Of course, despite the enormous energy that this ocean current carries, over time its strength weakens. From it in the process of movement are separated the so-called rings, similar to branches near rivers.
Their diameter is approximately 200 kilometers, and although they show dynamics in the North Atlantic, their number is always more than ten.
I must say, they also play a role in creating climatic conditions.
For example, if one of these rings goes to the south side of the ocean, then it brings cold water to the relatively warm part of the Atlantic. If the ring goes north, it carries warm water to colder regions of the ocean.
Sea currents and eddies
Whirlwinds have been and remain the constant companion of sea currents. The current itself is a front, in other words, a liquid that has characteristics different from other parts of the ocean. This front is constantly changing its position in the ocean, and eddies are formed next to it, sometimes reaching hundreds of kilometers in diameter.
An example is the Strait of Gibraltar. Of course, the water does not stand in it, as many might think, but is constantly moving. Moreover, it moves in two directions - from above, the liquid enters the Mediterranean Sea, and from below, on the contrary, it leaves a huge body of water.
Why exactly? The answer is quite simple: the water in the ocean is less salty than in the Mediterranean Sea. The saltier the water, the heavier it is, and the heavier it is, the lower it sinks.
And in this situation, a vortex appears, despite the fact that there are all the necessary conditions for the occurrence of a flow along the pressure gradient.
But the Coriolis force does not allow this to happen, and, compensating for the difference in hydrostatic pressures, makes the water, due to the prevailing conditions, break out of the depths in a direction perpendicular to the bottom. Thus, a monstrous vortex arises, reaching a diameter of about 100 kilometers.
Another interesting example, which for a long time could not be explained to scientists, is the Agulhas current. It moves along the eastern coast of Africa to the south, and, reaching the end of the mainland, turns back into the Indian Ocean.
In the place where the water changes its direction, eddies form near the current, directed to the Atlantic Ocean. For three years, each of these eddies travels across the ocean, after which, once off the coast of South America, it is lost in powerful coastal currents.
By themselves, these vortices are an amazing phenomenon. Their diameter is much greater than their thickness, and in essence they are formations that look like water disks rotating on the surface of the ocean.
For a long time, scientists could not solve this riddle, because according to the laws of physics, these disks should have disintegrated when they collided with a less mobile liquid.
But, as it turned out, while still in the Agulhas current, these eddies rotate like solid bodies. Only due to the fact that the characteristics of the water in the Indian Ocean are different from those of the water in the Atlantic, these unique formations successfully travel from one end of the world to another.
Maybe or maybe not
What happens to the water in the ocean, in particular, the behavior of eddies, is a living confirmation of the words that the World Ocean with its “tricks” can surprise almost any person. Equatorial currents deserve special attention, where the Coriolis force has almost no effect.
However, the Antarctic Circular Current plays an incredibly important role. This is the only current on our planet that passes through all the meridians and the only current that can be called absolutely closed. It is also called the "current of the West Winds".
The most powerful sea currents, however, are located in the west of the Atlantic Ocean. The Gulf Stream in the Atlantic, together with Kuroshio in the Pacific, literally decide where it will be cold and where it will be warm.
The continents owe favorable climatic conditions in one region and unfavorable in another to them. And it is extremely difficult to talk about the disappearance of the Gulf Stream, given the location of the land relative to the oceans.
If we imagine that the Gulf Stream will change and lengthen closer to Europe, then it will become warmer there, while Russia risks a little “freezing” to the Arctic. Otherwise, it's hard to say exactly what will happen.
Most likely, the UK will experience a serious cooling, but there will be no more ice in the Arctic Ocean, after which it will be included in the overall energy exchange system between the oceans and the atmosphere.
Subsequently, new air currents will arise, and these, in turn, will create new Iorian currents. And what will happen to the climate on Earth in the end is impossible to say for sure.
However, returning to the main question of whether this is possible at all, one can only proceed from the fact that the only danger at the moment is the ice around Greenland.
Slowly but surely, the glaciers of Greenland continue to melt, gradually raising the level of the oceans. However, there is still no reason to believe that a catastrophe is to be expected in the near future.
What will happen next? As already noted, it is impossible to say for sure. Many, however, are trying. And, based on the calculations that were provided, according to one version, the ocean on Earth will evaporate from the incredible heat, according to another, the equator will be covered with a meter-long crust of ice.
Therefore, such scenarios should not be taken seriously. The Earth is a self-regulating system that is capable of supporting life for millions of years, which is what it has been doing all this time.
If we talk about what official science thinks about the disappearance of the Gulf Stream or any other fundamental change in the World Ocean, then all modern publications and the facts cited in them indicate that this will not happen. The system that was formed on Earth has acquired too much stability to change beyond recognition in the blink of an eye.
How to study sea currents
To study ocean currents, at the end of the last century, devices were developed that are buoys called ARGO. They are located along all major boundaries of the oceans.
The distance between each buoy is approximately 300 kilometers. At first it was planned that their total number would be equal to three thousand, but this mark was reached back in 2007, and their number is still increasing. ARGO buoys measure the electrical conductivity of water, its optical characteristics and density.
The main functional purpose of these "floats" is to dive to different depths to collect data on water and sea currents. This is possible due to the change in the volume of the buoy. Inside it is a flexible reservoir in the form of a rubber bag, where water is pumped for diving, and the buoy is hidden in the depths of the ocean.
Most of the time the apparatus is underwater, working in cycles of 10 days. Surfing at the end of this period for only one day to send all the collected information to the satellite, he immediately begins a new cycle, studying the sea currents.
That's all, good luck to you!
Sea currents video
