Navigators learned about the presence of ocean currents almost immediately, as soon as they began to surf the waters of the oceans. True, the public paid attention to them only when, thanks to the movement of ocean waters, many great geographical discoveries, for example, Christopher Columbus sailed to America thanks to the North Equatorial Current. After that, not only sailors, but also scientists began to pay close attention to ocean currents and strive to explore them as best and as deeply as possible.
Already in the second half of the XVIII century. sailors studied the Gulf Stream quite well and successfully applied their knowledge in practice: they went with the flow from America to Great Britain, and kept a certain distance in the opposite direction. This allowed them to be two weeks ahead of ships whose captains were not familiar with the terrain.
Oceanic or sea currents are large-scale movements of the water masses of the World Ocean at a speed of 1 to 9 km / h. These streams do not move randomly, but in a certain channel and direction, which is the main reason why they are sometimes called the rivers of the oceans: the width of the largest currents can be several hundred kilometers, and the length can reach more than one thousand.
It has been established that water flows do not move straight, but deviating slightly to the side, they obey the Coriolis force. In the Northern Hemisphere they almost always move clockwise, in the Southern Hemisphere it is vice versa.. At the same time, currents located in tropical latitudes (they are called equatorial or trade winds) move mainly from east to west. The strongest currents were recorded along the eastern coasts of the continents.
Water flows do not circulate on their own, but they are set in motion by a sufficient number of factors - the wind, the rotation of the planet around its axis, the gravitational fields of the Earth and the Moon, the bottom topography, the outlines of continents and islands, the difference in temperature indicators of water, its density, depth in various places of the ocean and even its physico-chemical composition.
Of all types of water flows, the most pronounced are the surface currents of the World Ocean, the depth of which is often several hundred meters. Their occurrence was influenced by trade winds, constantly moving in tropical latitudes in a west-east direction. These trade winds form huge streams of the North and South Equatorial currents near the equator. A smaller part of these flows returns to the east, forming a countercurrent (when the movement of water occurs in the opposite direction from the movement of air masses). Most, colliding with the continents and islands, turns to the north or south.
Warm and cold water streams
It must be taken into account that the concepts of "cold" or "warm" currents are conditional definitions. So, despite the fact that the temperature indicators of the water flows of the Benguela Current, which flows along the Cape of Good Hope, are 20 ° C, it is considered cold. But the North Cape Current, which is one of the branches of the Gulf Stream, with temperatures ranging from 4 to 6 ° C, is warm.
This happens because the cold, warm and neutral currents got their names based on a comparison of the temperature of their water with the temperature indicators of the ocean surrounding them:
- If the temperature indicators of the water flow coincide with the temperature of the waters surrounding it, such a flow is called neutral;
- If the temperature of the currents is lower than the surrounding water, they are called cold. They usually flow from high latitudes to low latitudes (for example, the Labrador Current), or from areas where, due to the large flow of rivers ocean water has a low salinity of surface waters;
- If the temperature of the currents is warmer than the surrounding water, then they are called warm. They move from the tropics to subpolar latitudes, such as the Gulf Stream.
Main water flows
At the moment, scientists have recorded about fifteen major oceanic water flows in the Pacific, fourteen in the Atlantic, seven in the Indian and four in the Arctic Ocean.
It is interesting that all the currents of the Arctic Ocean move at the same speed - 50 cm / s, three of them, namely the West Greenland, West Svalbard and Norwegian, are warm, and only the East Greenland belongs to the cold current.
But almost all ocean currents indian ocean are warm or neutral, while the Monsoon, Somali, Western Australian and the Cape of Needles (cold) move at a speed of 70 cm / sec., the speed of the rest varies from 25 to 75 cm / sec. The water flows of this ocean are interesting because, along with the seasonal monsoon winds, which change their direction twice a year, ocean rivers also change their course: in winter they mainly flow west, in summer - east (a phenomenon characteristic only of the Indian Ocean). ).
Since the Atlantic Ocean stretches from north to south, its currents also have a meridional direction. Water streams located in the north move clockwise, in the south - against it.
A prime example of flow Atlantic Ocean is the Gulf Stream, which, starting in the Caribbean Sea, carries warm waters to the north, breaking up along the way into several side streams. When the waters of the Gulf Stream end up in the Barents Sea, they enter the Arctic Ocean, where they cool and turn south in the form of a cold Greenland current, after which at some stage they deviate to the west and again adjoin the Gulf Stream, forming a vicious circle.
The currents of the Pacific Ocean are mainly latitudinal and form two huge circles: northern and southern. Since the Pacific Ocean is extremely large, it is not surprising that its water flows have a significant impact on most of our planet.
For example, trade winds move warm water from the western tropical coasts to the eastern ones, which is why the western part of the Pacific Ocean in the tropical zone is much warmer than the opposite side. But in the temperate latitudes of the Pacific Ocean, on the contrary, the temperature is higher in the east.
deep currents
Enough long time scientists believed that deep ocean waters almost motionless. But soon, special underwater vehicles discovered both slow and fast-flowing water flows at great depths.
For example, under the Equatorial Pacific Ocean at a depth of about one hundred meters, scientists have identified the Cromwell underwater stream, moving eastward at a speed of 112 km / day.
A similar movement of water flows, but already in the Atlantic Ocean, was found by Soviet scientists: the width of the Lomonosov current is about 322 km, and the maximum speed of 90 km / day was recorded at a depth of about one hundred meters. After that, another underwater stream was discovered in the Indian Ocean, however, its speed turned out to be much lower - about 45 km / day.
The discovery of these currents in the ocean gave rise to new theories and mysteries, the main of which is the question of why they appeared, how they formed, and whether the entire ocean area is covered by currents or there is a point where the water is still.
The influence of the ocean on the life of the planet
The role of ocean currents in the life of our planet cannot be overestimated, since the movement of water flows directly affects the planet's climate, weather, and marine organisms. Many compare the ocean to a huge heat engine powered by solar energy. This machine creates a continuous water exchange between the surface and deep layers of the ocean, providing it with oxygen dissolved in water and affecting the life of marine life.
This process can be traced, for example, by considering the Peruvian current, which is located in pacific ocean. Thanks to the rise of deep waters, which lift phosphorus and nitrogen upward, animal and plant plankton successfully develop on the ocean surface, as a result of which the food chain is organized. Plankton is eaten by small fish, which, in turn, becomes a victim of larger fish, birds, marine mammals, which, with such food abundance, settle here, making the region one of the most highly productive areas of the World Ocean.
It also happens that a cold current becomes warm: the average temperature environment rises by several degrees, causing warm tropical showers to fall on the ground, which, once in the ocean, kill fish accustomed to cold temperatures. The result is deplorable - a huge amount of dead small fish ends up in the ocean, large fish leave, fishing stops, birds leave their nests. As a result, the local population is deprived of fish, crops that were beaten by downpours, and profits from the sale of guano (bird droppings) as fertilizer. It can often take several years to restore the former ecosystem.
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 runoff river waters in 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 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 have special meaning for navigation, since they carry ice to lower latitudes and cause in some areas a greater frequency of fogs 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.
currents of surface waters of oceans and seas, resulting from the action of wind on the water surface. Wind flow develops under the combined influence of friction forces, turbulent viscosity, pressure gradient, deflecting forces of the Earth's rotation, and so on. The wind component of these currents, without taking into account the pressure gradient, is called the drift current. Under conditions of winds that are stable in direction, powerful wind currents develop, such as the North and South Trade-wind currents, the course of westerly winds, and others. N. S. Lineikin, American G. Stoml.
- - see Air currents ...
Dictionary of winds
- - waves raised by the wind on the surface of a reservoir or sea: ripples, two-dimensional waves, crowding, swell, dead swell, etc. The ratio of the speed of the waves to the speed of the wind that caused them is about 0.8, the period of the waves is up to 10 -16 s, ...
Dictionary of winds
- - air flows, atmospheric flows - wind systems over a significant area and in a significant thickness of the atmosphere, which have a certain stability in time and space ...
Dictionary of winds
- - wind currents, temporary, periodic or permanent, arising on the surface of the water under the influence of wind. They deviate from the direction of the wind in the northern hemisphere to the right by an angle of 30-45 ° ...
Dictionary of winds
- - connections located at the level of the upper and lower chords of the main trusses of the superstructure ...
Construction dictionary
- - deep currents is a generalized name for currents that develop in the ocean below a layer of water that is under the direct influence of the wind ...
Geographic Encyclopedia
- - see Eolian signs of ripples ...
Geological Encyclopedia
- - asymmetric ripple marks with a steep lee slope. The ridges are usually arcuately curved, their arrangement in plan is close to parallel...
Geological Encyclopedia
- - associated with the parallel arrangement of elongated m-fishing. Occurs in the process of plastic flow and recrystallization; its surfaces are usually oriented ┴ compressive forces. Syn.: cleavage expiration...
Geological Encyclopedia
- - see Currents...
Marine vocabulary
- - currents arising in the seas and oceans as a result of the formation of a pressure difference in the water column in them. The pressure difference is created under the influence of surges and surges of water by winds, uneven distribution ...
- - currents in water bodies caused by the action of wind. See wind currents...
Great Soviet Encyclopedia
- - horizontal movements of water masses, replenishing the loss of water in any part of the ocean, sea, lake. They can develop both in the surface and deep layers ...
Great Soviet Encyclopedia
- - October. pioneer. pioneer leader. be ready! always ready! Timurovets. Komsomol. Komsomol member. scout. scouting. scout. girl scout. hippie. hipster...
Ideographic dictionary Russian language
- - influences of time, prevailing views Cf. To carry out legislative work does not mean sometimes to carry it out in practice, especially if unfavorable for it...
Explanatory-phraseological dictionary of Michelson
- - Currents of the influence of time, prevailing views. Wed To carry out legislative work does not mean sometimes to carry it out in practice, especially if there are trends that are unfavorable for it. A. th...
Michelson Explanatory Phraseological Dictionary (original orph.)
"Wind currents" in books
Against the stream
From the book Comandante Reflections author Castro FidelAgainst the Current on May 23 of this year, Obama spoke at the Cuban American National Foundation, created by Ronald Reagan, and I expressed my impressions of this on May 25 in a reflection entitled "The Cynical Politics of Empire." In them, I quoted his words to
Against the stream
From the book Priceless Gift author Konchalovskaya NatalyaAgainst the current, Pyotr Petrovich Sr. was preoccupied and dejected. He sat in the bedroom, sunk deep into an easy chair. Viktoria Timofeyevna was ill, and, reclining on the couch, wrapped in a blanket, she slowly drank a hot lime blossom decoction from an old silver mug.
Against the stream
From the book of Einstein. His life and his universe author Isaacson WalterAgainst the Current Was Infeld Right? Was tenacity Einstein's trait? To some extent, this happy property has always been inherent in him. It manifested itself most fully during his long solitary attempts to generalize the theory of relativity. Since the days of school in it
Against the stream
From the book Tatyana Doronina. Once again about love author Goreslavskaya Nelli BorisovnaAgainst the tide For Doronina, from that moment on, her Golgotha began, lasting almost a decade and a half. Not only that, on her shoulders was the heaviest load of new duties, so unfamiliar, to which she did not aspire. On her, until recently everyone's favorite famous
AGAINST THE STREAM
From the book With Your Eyes author Adelheim PavelAGAINST THE CURRENT 1. Marriage Should the wretched Galileans go Against the current! AK Tolstoy Those who graduated from theological schools face two problems: family and ordination. Finding a believing girl is not difficult. Find a girlfriend for life, ready to share with you both beliefs and adversity
"AGAINST THE STREAM"
From the book Unknown Lenin author Loginov Vladlen Terentyevich"AGAINST THE CURRENT" When the political struggle becomes especially acute, a certain "regularity" often manifests itself: political leaders, opposing each other, not only stop understanding, but also stop listening to the enemy. They simply do not perceive any ideas, not
AGAINST THE STREAM
From the book Made in America [How I Created Wal-Mart] by Walton SamAGAINST THE CURRENT “From the very first day of Wal-Mart, Mr. Walton made it clear that these stores were not Ben Franklin with low prices on some items. He wanted this network to actually operate on the principle of discount trading, and said: “We
catch currents
From the book Leadership Based on Principles by Covey Steven RCatch the currents Many people know the saying: “Give a man a fish and you feed him for a day. Teach him how to fish and you will feed him for a lifetime.” This is an old axiom, but today it is more timely than ever. In fact, this is the main principle of our trainings. Them
World Currents
From the book Confidence [Skill System for Further Energy-Informational Development. V stage, first stage] author Verishchagin Dmitry Sergeevichcurrent movement
From the book About a tasty and healthy life author Koblin SeymourThe movement of the current The movement of the current corresponds to the winter season and the night time of the day (associated with lower temperatures). Its imbalance often manifests itself in a feeling of coldness, as well as difficulty in adapting to surrounding circumstances (on the physical,
Undercurrents
From the book The Third Wave author Toffler AlvinUndercurrents Multi-purpose corporations, among other things, must have very energetic executive structures. This implies the ability of directors to recognize goals, weigh them, find their interrelationships, and implement policies that will
AGAINST THE STREAM
From the book Where the river of time flows author Novikov Igor DmitrievichAGAINST THE CURRENT The general theory of relativity was created by A. Einstein on the basis of the minimum number of experimental data on gravitation, selected by him with ingenious intuition. For many decades that have passed since then, all the predictions of this theory that could be
VII. COUNTERCURRENTS
From the book The Thirteenth Tribe. The collapse of the Khazar empire and its legacy. author Koestler ArthurVII. COUNTERCURRENTS 1Given the evidence presented in previous chapters, it is easy to see why Polish historians—who are, after all, closest to the core of the problem—agree that “in the early period, the core of the Jewish population emerged from
4. "Currents"
From the author's book4. "Trends" Rejecting direct decisions, ignoring the will of the workers, the "S.-D. faction" extends in detail about the usefulness of all "trends of Marxism". All over the world, Marxists start from workers' organizations, in our country they want to start from elusive "trends". In Germany, and throughout the world, the Social-Democrats
wind currents
From the book Big Soviet Encyclopedia(BE) author TSB
The direction of the currents is influenced by the force of the Earth's rotation: in the Northern Hemisphere, the currents move to the right, in the Southern - to the left.
The current is called warm if its temperature is warmer than the temperature of the surrounding waters, otherwise, the current is called cold.
Density currents are caused by pressure differences, which are caused by an uneven distribution of density sea water. Density currents are formed in the deep layers of the seas and oceans. A striking example of density currents is the warm Gulf Stream.
Wind currents are formed under the action of winds, as a result of the friction forces of water and air, turbulent viscosity, pressure gradient, deflecting forces of the Earth's rotation, and some other factors. Wind currents are always superficial. Northern and South Trade winds, the current of the West Winds, Intertrade Pacific and Atlantic.
1) Gulf Stream - a warm sea current in the Atlantic Ocean. In a broad sense, the Gulf Stream is a system of warm currents in the North Atlantic Ocean from Florida to the Scandinavian Peninsula, Svalbard, the Barents Sea and the Arctic Ocean.
Thanks to the Gulf Stream, the countries of Europe adjacent to the Atlantic Ocean have a milder climate than other regions at the same geographical latitude: masses of warm water heat the air above them, which is transferred to Europe by westerly winds. Deviations of air temperature from average latitude values in January reach 15–20 °C in Norway, and more than 11 °C in Murmansk.
2) The Peruvian current is a cold surface current in the Pacific Ocean. Moves from south to north between 4° and 45° south latitude along the western coasts of Peru and Chile.
3) The Canary Current is a cold and, subsequently, moderately warm sea current in the northeastern part of the Atlantic Ocean. Directed from north to south along the Iberian Peninsula and Northwest Africa as a branch of the North Atlantic Current.
4) The Labrador Current is a cold sea current in the Atlantic Ocean, flowing between the coast of Canada and Greenland and rushing south from the Baffin Sea to the Newfoundland Bank. There it meets the Gulf Stream.
5) The North Atlantic Current is a powerful warm ocean current that is the northeastern continuation of the Gulf Stream. Starts at the Great Newfoundland Bank. West of Ireland, the current is divided into two parts. One branch (the Canary Current) runs south and the other north along the coast of northwestern Europe. The current is believed to have a significant influence on the climate in Europe.
6) The cold California Current emerges from the North Pacific Current, moves along the coast of California from the northwest to the southeast, merges in the south with the North Tradewind Current.
7) Kuroshio, sometimes the Japan Current - a warm current off the southern and eastern coasts of Japan in the Pacific Ocean.
8) The Kuril current or Oyashio is a cold current in the northwest Pacific Ocean, which originates in the waters of the Arctic Ocean. In the south, near the Japanese Islands, it merges with Kuroshio. It flows along Kamchatka, the Kuriles and the Japanese islands.
9) The North Pacific Current is a warm ocean current in the North Pacific Ocean. It is formed as a result of the confluence of the Kuril Current and Kuroshio. Moves from the Japanese islands to the shores of North America.
10) Brazilian current - a warm current of the Atlantic Ocean off the eastern coast South America, directed to the southwest.
P.S. To understand where the various currents are, study the set of maps. It will also be useful to read this article
Any theory of flows is based on systems of hydrodynamic equations for the components of the velocity vector, which are simplified in each specific case in accordance with the problem. W. Ekman used two equations for the components of the velocity vector u and v- flow projections on the axis X and at, which takes into account only two forces that balance one another: the friction force caused by the wind on the surface, and the Coriolis force.
The task was set by F. Nansen, who during the expedition on the Fram (1893 - 1896) noticed the deviation of the ice drift to the right from the wind, explained it by the influence of the Coriolis force and asked to check this with a mathematical solution. The first solution was carried out by V. Ekman in 1902 and corresponded to the most simple and at the same time general conditions: the ocean is homogeneous in level, density and viscosity, infinitely deep, boundless and subject to the action of a constant wind (taken along the y axis). The wind is also unlimited and constant, the movement is steady (stationary). Under these conditions, the solution looked like:
where V o is the current velocity on the ocean surface; µ - dynamic coefficient of viscosity; with- density of water; sch- angular velocity of the Earth's rotation; c- location latitude, axis z pointing down.
The equations show that the surface current deviates from the wind direction by 45° to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. Under the surface, the current decreases with depth in absolute value according to an exponential law and continues to deviate to the right in the Northern Hemisphere, to the left - in the Southern. The projection onto the ocean surface of a spatial curve passing through the ends of the velocity vectors (envelope) will be expressed as a logarithmic spiral - the Ekman spiral (Fig. 1).
Rice. one.
On the horizon, the current has a direction opposite to the surface one, and the speed is equal (about 4%) to the surface one, i.e., the speed practically decays (we should recall the same regularity during waves). This horizon is called friction depth, was determined by Ekman using the formula
and the whole layer is called Ekmanovsky, or friction layer.
The depth of friction thus depends on the latitude of the place. This depth varies from a minimum value at the pole to a maximum (infinity) at the equator, where the sine of latitude is zero. This means that, according to the theory, the wind current at the equator should spread to the bottom, which is not the case in nature. The thickness of the wind current layer is practically limited to several tens of meters.
It remains to determine where the water of the entire layer is transferred, if the currents at different horizons have different directions. The answer can be found by integrating the components of the current velocity along the vertical. It turned out that the transfer of water in a wind current, according to Ekman, occurs not along the wind, but perpendicular to it, along the x-axis. This is easy to understand, since the theory is based on the assumption of equilibrium between the friction force (it is directed along the ordinate axis in a positive direction) and the Coriolis force. This means that the latter must be directed along the ordinate axis in the direction of negative values, and for this, the mass transfer must be directed along the abscissa axis in the positive direction (for northern hemisphere right).
Ekman's theory also makes it possible to obtain a formula for the relationship between wind speeds W and surface currents V 0:
In formula (3), the coefficient of proportionality at wind speed W(0.0127) is called wind coefficient.
Then Ekman (1905) applied his theory to a sea of finite depth. It turned out that the solution depends on the main argument - the ratio of the depth of space to the depth of friction. The speed of the wind current, the angle of deviation of the current from the wind, and the shape of the curve enveloping the current vectors depend on it. When the angle of flow deviation on the surface is equal to 21.5°, when the angle is less than 5°, the direction changes little deeper from the surface, and when the direction of the flow is the same in the entire layer. The value of the velocity at the bottom turns to zero.
Near the coast, the structure of the wind current becomes more complicated. In the ideal case, when the coast is a vertical wall with a depth of more than 2 D and the bottom approaches this wall perpendicularly, a three-layer system of currents is formed. Top layer depth D has a normally developed structure of the Ekman spiral, under it lies a layer with a vertically constant current velocity directed along the coast - this gradient flow. In the layer located upward from the bottom at a distance D (lower friction layer), the flow velocity decreases and changes direction along the same spiral from the value of the intermediate layer velocity to zero near the bottom. A diagram of such a structure of the coastal current is shown in Fig. 2. It illustrates the coastal circulation of waters with a negative wind, when the resulting water flow is directed away from the coast. At the same time, the wind is directed so that the coast lies on the left side (the diagram is given for the Northern Hemisphere). With the opposite wind, a similar pattern is obtained for the surge case, and the wind perpendicular to the coast will not give either a surge or a surge. This is a neutral wind. Such a scheme does not occur in its pure form, although near the deep coasts (for example, near the Caucasian and Crimean coasts of the Black Sea), a similar situation can be observed, leading to upwelling in the case of surge (see 10.5.2).
Rice. 2. Scheme of the flow structure near the deep coast in the section ( a) and plan ( b) (according to Ekman)
Near shallow coasts, where the greatest surge effect is created by winds in the direction perpendicular to the coastline (for example, in the Gulf of Finland and Taganrog), and its direction, parallel to the coastline, will be neutral.
On the basis of Ekman's theory, studies of wind currents have developed and continue to develop. For example, theories of wind currents have been developed for shallow seas of various forms. The role of wind level changes in the formation of the flow pattern of the World Ocean waters is determined. It turned out that under the influence of uneven wind, slopes occur water surface, which at first little change the density field. If the wind blows for a long time, then the density field is rebuilt. Less dense water upper layers moves aside under the influence of the Coriolis force and wind surge high level(the right side of the current in the Northern Hemisphere), while denser water at depth flows towards a lower level and pressure (the left side of the current).