Sea waves vs ocean waves - what's the difference? Sea waves are an illusion of human vision.

6. Sea waves.

The surface of the sea is always moving, even with complete calm. But then the wind blew, and ripples immediately appeared on the water, which turned into waves the faster the stronger the wind blew. But no matter how strong the wind is, it cannot cause waves larger than certain maximum sizes.

Waves generated by wind are considered short. Depending on the strength and duration of the wind, their length and height range from several millimeters to tens of meters (in a storm, the length of wind waves reaches 150-250 meters).

Observations of the sea surface show that waves become strong even at wind speeds of more than 10 m/s, while the waves rise to a height of 2.5-3.5 meters, crashing onto the shore with a roar.

But then the wind turns storm, and the waves reach enormous sizes. There are many places on the globe where very strong winds blow. For example, in the northeastern part of the Pacific Ocean east of the Kuril and Commander Islands, as well as east of the main Japanese island of Honshu in December-January maximum speeds winds are 47-48 m/s.

In the South Pacific, maximum wind speeds are observed in May in the area northeast of New Zealand (49 m/s) and near the Antarctic Circle in the area of Balleny and Scott Islands (46 m/s).

We perceive speeds expressed in kilometers per hour better. So the speed of 49 m/s is almost 180 km/h. Already at a wind speed of more than 25 m/s, waves 12-15 meters high rise. This degree of excitement is rated 9–10 points as a severe storm.

Measurements have established that the height of the storm wave in the Pacific Ocean reaches 25 meters. There are reports that waves up to 30 meters high have been observed. True, this assessment was made not on the basis of instrumental measurements, but approximately, by eye.

IN Atlantic Ocean maximum height wind waves reach 25 meters.

The length of storm waves does not exceed 250 meters.

But the storm stopped, the wind died down, but the sea still did not calm down. Like the echo of a storm on the sea arises swell. Swell waves (their length reaches 800 meters or more) move over enormous distances of 4-5 thousand km and approach the shore at a speed of 100 km/h, and sometimes higher. In the open sea, low and long swell waves are invisible. When approaching the shore, the speed of the wave decreases due to friction with the bottom, but the height increases, the front slope of the wave becomes steeper, foam appears at the top, and the crest of the wave crashes onto the shore with a roar - this is how the surf appears - a phenomenon equally colorful and majestic, as dangerous as it is. The force of the surf can be colossal.

When faced with an obstacle, the water rises to a great height and damages lighthouses, port cranes, breakwaters and other structures. Throwing stones from the bottom, the surf can damage even the highest and most distant parts of lighthouses and buildings. There was a case when the surf tore a bell from one of the English lighthouses from a height of 30.5 meters above sea level. The surf on our Lake Baikal sometimes in stormy weather throws stones weighing up to a ton at a distance of 20-25 meters from the shore.

During storms in the Gagra region, the Black Sea washed away and absorbed coastal strip 20 meters wide. When approaching the shore, the waves begin their destructive work from a depth equal to half their length in the open sea. Thus, with a storm wave length of 50 meters, characteristic of seas such as the Black or Baltic, the impact of waves on the underwater coastal slope begins at a depth of 25 m, and with a wave length of 150 m, characteristic of the open ocean, such impact begins already at a depth of 75 m.

Current directions affect the size and strength of sea waves. With counter currents, the waves are shorter but higher, and with passing currents, on the contrary, the height of the waves decreases.

Near the boundaries of sea currents, waves of unusual shapes, resembling a pyramid, and dangerous whirlpools often appear that suddenly appear and just as suddenly disappear. In such places, navigation becomes especially dangerous.

Modern ships have high seaworthiness. But it happens that, having traveled many miles across a stormy ocean, ships find themselves in even greater danger than at sea when they arrive in their home bay. The powerful surf, breaking the multi-ton reinforced concrete breakwaters of the dam, is capable of turning even a large ship into a pile of metal. In a storm, it is better to wait until entering the port.

To combat the surf, specialists in some ports tried to use air. A steel pipe with numerous small holes was laid on the seabed at the entrance to the bay. Air under high pressure was supplied into the pipe. Escaping from the holes, streams of air bubbles rose to the surface and destroyed the wave. This method has not yet found widespread use due to insufficient efficiency. Rain, hail, ice and thickets of marine plants are known to calm waves and surf.

Sailors have long noticed that fat poured overboard smoothes the waves and reduces their height. Animal fat, such as whale blubber, works best. The effect of vegetable and mineral oils is much weaker. Experience has shown that 50 cm 3 of oil is enough to reduce disturbances over an area of 15 thousand square meters, that is, 1.5 hectares. Even a thin layer of oil film noticeably absorbs the energy of vibrational movements of water particles.

Yes, that's all true. But, God forbid, we under no circumstances recommend that captains of sea vessels stock up on fish or whale oil before a voyage in order to then pour these fats into the waves to calm the ocean. After all, things can reach such an absurdity that someone will start pouring oil, fuel oil, and diesel fuel into the sea in order to appease the waves.

It seems to us that best way combating waves consists of a well-organized weather service that notifies ships in advance about the expected place and time of the storm and its expected strength, good navigational and pilot training of sailors and coastal personnel, as well as constant improvement of the design of ships in order to improve their seaworthiness and technical reliability.

For scientific and practical purposes, it is necessary to know the full characteristics of the waves: their height and length, the speed and range of their movement, the power of an individual water shaft and the wave energy in a particular area.

The first measurements of waves were made in 1725 by the Italian scientist Luigi Marsigli. At the end of the 18th – beginning of the 19th centuries, regular observations of waves and their measurements were carried out by Russian navigators I. Kruzenshtern, O. Kotzebue and V. Golovin during their voyages across the World Ocean. The technical basis for measurements in those days was very weak; of course, there were no special instruments for measuring waves on the sailing ships of that time.

Currently, for these purposes, there are very complex and precise instruments that are equipped with research vessels that carry out not only measurements of wave parameters in the ocean, but also much more complex scientific work. The ocean still holds many secrets, the disclosure of which could bring significant benefits to all of humanity.

When they talk about the speed of movement of waves, that waves run up and roll onto the shore, you need to understand that it is not the water mass itself that moves. The water particles that make up the wave practically do not move forward. Only the waveform moves in space, and the water particles in the agitated sea make oscillatory movements in the vertical and, to a lesser extent, in the horizontal plane. The combination of both oscillatory movements leads to the fact that the water particles in the waves actually move in circular orbits, the diameter of which is equal to the height of the wave. The oscillatory movements of water particles quickly decrease with depth. Precise instruments show, for example, that with a wave height of 5 meters (storm wave) and a length of 100 meters, at a depth of 12 meters the diameter of the wave orbit of water particles is already 2.5 meters, and at a depth of 100 meters - only 2 centimeters.

Long waves, unlike short and steep ones, transmit their motion to great depths. In some photographs of the ocean floor down to a depth of 180 meters, researchers noted the presence of sand ripples formed under the influence of oscillatory movements of the bottom layer of water. This means that even at such a depth, the surface waves of the ocean make themselves felt.

Is it necessary to prove what danger a storm wave poses to ships?

In the history of navigation, there are countless tragic incidents at sea. Small longboats and fast sailing ships, along with their crews, perished. Modern ocean liners are not immune to the insidious elements.

On modern ocean-going ships, among other devices and instruments that ensure safe navigation, pitch stabilizers are used, which prevent the ship from getting an unacceptably large roll on board. In some cases, powerful gyroscopes are used for this, in others, retractable hydrofoils are used to level the position of the ship’s hull. Computer systems on ships are in constant communication with meteorological satellites and other spacecraft, which tell navigators not only the location and strength of storms, but also the most favorable course in the ocean.

In addition to surface waves, there are also internal waves in the ocean. They form at the interface between two layers of water of different densities. These waves travel slower than surface waves, but can have greater amplitude. Internal waves are detected by rhythmic changes in temperature at different depths of the ocean. The phenomenon of internal waves has not yet been sufficiently studied. It has only been established that waves arise at the boundary between layers with lower and higher densities. The situation may look like this: there is complete calm on the surface of the ocean, but at some depth a storm is raging; along the length, internal waves are divided, like ordinary surface ones, into short and long. For short waves, the length is much less than the depth, while for long waves, on the contrary, the length exceeds the depth.

There are many reasons for the appearance of internal waves in the ocean. The interface between layers with different densities can be thrown out of balance by a moving large vessel, surface waves, or sea currents.

Long internal waves manifest themselves, for example, in this way: a layer of water, which is a watershed between more dense (“heavy”) and less dense (“light”) water, first rises slowly, for hours, and then suddenly falls by almost 100 meters. This wave is very dangerous for submarines. After all, if a submarine sank to a certain depth, it means it was balanced by a layer of water of a certain density. And suddenly, unexpectedly, a layer of less dense water appears under the hull of the boat! The boat immediately falls into this layer and sinks to the depth where the less dense water can balance it. But the depth may be such that the water pressure exceeds the strength of the hull of the submarine, and it will be crushed in a matter of minutes.

According to the conclusion of American experts who investigated the causes of the death of the nuclear submarine Thresher in 1963 in the Atlantic Ocean, this submarine found itself in exactly this situation and was crushed by enormous hydrostatic pressure. Naturally, there were no witnesses to the tragedy, but the version of the cause of the disaster is confirmed by the results of observations carried out by research ships in the area where the submarine sank. And these observations showed that internal waves with a height of more than 100 meters often arise here.

A special type are the waves that arise on the sea when there is a change atmospheric pressure. They are called seiches And microseiches. Oceanology studies them.

So, we talked about both short and long waves at sea, both surface and internal. Now let us remember that long waves arise in the ocean not only from winds and cyclones, but also from processes occurring in the earth’s crust and even in the deeper regions of the “interior” of our planet. The length of such waves is many times greater than the longest ocean swell waves. These waves are called tsunami. The height of tsunami waves is not much higher than large storm waves, but their length reaches hundreds of kilometers. The Japanese word "tsunami" roughly translates to "harbour wave" or "coastal wave" . To some extent, this name conveys the essence of the phenomenon. The point is that in open ocean a tsunami poses no danger. At a sufficient distance from the coast, the tsunami does not rage, does not cause destruction, and cannot even be noticed or felt. All tsunami disasters occur on the shore, in ports and harbors.

Tsunamis occur most often from earthquakes caused by the movement of tectonic plates earth's crust, as well as from strong volcanic eruptions.

The mechanism for the formation of a tsunami is most often as follows: as a result of the displacement or rupture of a section of the earth's crust, a sudden rise or fall of a significant section of the seabed occurs. As a result, a rapid change in the volume of the water space occurs, and elastic waves appear in the water, propagating at a speed of about one and a half kilometers per second. These powerful elastic waves generate tsunamis on the ocean surface.

Having arisen on the surface, tsunami waves scatter in circles from the epicenter. At the point of origin, the height of the tsunami wave is small: from 1 centimeter to two meters (sometimes up to 4-5 meters), but more often in the range from 0.3 to 0.5 meters, and the wave length is huge: 100-200 kilometers. Invisible in the ocean, these waves, approaching the shore, like wind waves, become steeper and higher, sometimes reaching a height of 10-30 and even 40 meters. Having hit the shore, tsunamis destroy and destroy everything in their path and, worst of all, bring death to thousands, and sometimes tens and even hundreds of thousands of people.

The speed of tsunami propagation can be from 50 to 1000 kilometers per hour. Measurements show that the speed of a tsunami wave varies proportionally square root from the depths of the sea. On average, a tsunami rushes across the open ocean at a speed of 700-800 kilometers per hour.

Tsunamis are not regular events, but they are no longer rare.

In Japan, tsunami waves have been recorded for more than 1,300 years. Average per Country rising sun destructive tsunamis struck every 15 years (small tsunamis that did not have serious consequences are not taken into account).

Most tsunamis occur in the Pacific Ocean. Tsunamis raged in the Kuril, Aleutian, Hawaiian, and Philippine islands. They also attacked the coasts of India, Indonesia, Northern and South America, as well as to European countries located on Atlantic coast and in the Mediterranean.

The last most destructive tsunami attack was the terrible flood of 2004 with enormous destruction and loss of life, which had seismic causes and originated in the center Indian Ocean.

In order to have an idea of the specific manifestations of a tsunami, you can refer to numerous materials that describe this phenomenon.

We will give just a few examples. This is how the results of the earthquake that occurred in the Atlantic Ocean not far from the Iberian Peninsula on November 1, 1755 were described in the press. It caused terrible destruction in the capital of Portugal, Lisbon. The ruins of the once majestic building still tower in the city center convent Karmo that was never restored. These ruins remind the people of Lisbon of the tragedy that struck the city on November 1, 1755. Shortly after the earthquake, the sea receded, and then a wave 26 meters high hit the city. Many residents, fleeing the falling debris of buildings, left the narrow streets of the city and gathered on the wide embankment. The surging wave washed away 60 thousand people into the sea. Lisbon was not completely flooded because it is located on several high hills, but in low-lying areas the sea flooded the land up to 15 kilometers from the coast.

On August 27, 1883, there was a powerful eruption of the Kratau volcano, located in the Sunda Strait of the Indonesian archipelago. Clouds of ash rose into the sky, a strong earthquake arose, generating a wave 30-40 meters high. In a few minutes, this wave washed away all the villages located on the low shores of western Java and southern Sumatra into the sea, killing 35 thousand people. At a speed of 560 kilometers per hour, tsunami waves swept through the Indian and Pacific oceans, reaching the shores of Africa, Australia and America. Even in the Atlantic Ocean, despite its isolation and remoteness, in some places (France, Panama) a certain rise in water was noted.

On June 15, 1896, the incoming tsunami waves destroyed the east coast Japanese island Honshu 10 thousand houses. As a result, 27 thousand inhabitants died.

It is impossible to fight a tsunami. But it is possible and necessary to minimize the damage they cause to people. Therefore, now in everyone there is a seismic active areas Where there is a threat of tsunami waves, special warning services have been created, equipped with the necessary equipment that receives signals about changes in the seismic situation from sensitive seismographs located in different places on the coast. The population of such areas is regularly instructed on the rules of behavior in the event of a threat of tsunami waves. Tsunami warning services in Japan and Hawaiian Islands More than once they have given timely warning signals about the approaching tsunami, thereby saving more than one thousand human lives.

All types of currents and waves are characterized by the fact that they carry colossal energy - thermal and mechanical. But humanity is not able to use this energy, unless, of course, we count attempts to use the energy of ebbs and flows. One of the scientists, probably a statistics buff, calculated that the power sea tides exceeds 1000000000 kilowatts, and of all the rivers of the globe - 850000000 kilowatts. The energy of one square kilometer of stormy sea is estimated at billions of kilowatts. What does this mean for us? Only that a person cannot use even a millionth part of the energy of tides and storms. To some extent, people use wind energy to generate electricity and other purposes. But that, as they say, is another story.

What does wave height depend on?? The height of the wave depends on the strength, duration and length of the wind run-up. The greater the wind spread, the higher it is. As a rule, waves do not exceed four meters. In areas where hurricanes often occur, they can reach 25 meters in height: such waves can be seen between New Zealand, Cape Horn ( extreme point South America) and Antarctica (the southern polar continent).

What happens to objects on waves? A floating object (for example, a ball) “dances” on the waves, that is, it moves up and down while remaining in place. This happens because the wave moves in a circle - up, forward, down and back again. The object performs the same movements: it remains in place, since only waves move on the surface of the water, while the water itself is motionless.

What happens when waves “meet”? The movement of waves creates rows of crests and troughs. Waves of different crests intersect. If the crest of one runs into the crest of the second, they overlap each other and the height of the wave almost doubles. If the crest runs into the bottom of the wave, then, accordingly, it decreases.

What is swell? After the storm, the wind subsides, but the raging sea does not immediately become smooth. Short and steep waves roll over long and smooth waves with round crests. Such wind waves are called swells. It can remain at sea after a storm for several days, even weeks, and spread to sea areas far from the place of origin.

How quickly does sea swell spread?? The wavelength of the sea swell is from 250 to 900 meters. In the open sea, it spreads at a speed of 70 kilometers per hour or more and can cover enormous distances without weakening. The ship's passengers are surprised by the sight of a sudden swell in windless sea areas.

What is surf? When the waves reach shallow areas, they slow down on the seabed, becoming shorter, but at the same time steeper and higher. They finally crash on the beach. This stranding of sea waves is called a surf. The breaking waves are especially powerful where storm wind waves rush ashore.

What types of surf exist?? There are two types of surf: in one case, the waves break on the beach, and in the other, on the rocks. Beach surf occurs on shallow coastlines, while rock surf occurs when waves crash on rocky shores. The waters of the beach surf wash the shores, and the rocky waves break off pieces of stones from the rocks, as a result of which caves are formed in them. They are called grottoes.

Why does coastal erosion occur?? Coastal erosion is the destruction of soil that causes the coastline to change over time. Such changes are caused primarily by the sea surf. Since steep shores consist of soft sedimentary deposits (sediments), sea waves destroy them especially strongly. Scientists call coastal erosion abrasion.

What is rough seas? The movement of waves caused by the wind is called rough seas. It's about about wind waves, swell and surf. Wind waves do not come from other parts of the seas, but arise from the direct impact of wind on the surface of the water. The roughness of the sea depends primarily on the strength of the wind.

What is wind power? The winds have strong impact the sea, its waves and currents. Great value At the same time, the force of the wind is the name given to its speed, which is determined using the Beaufort scale. This twelve-point scale was created in 1806 by British Admiral Francis Beaufort (1774-1854). According to it, 0 means calm, 12 means hurricane.

What is sea foam? Sea foam occurs when a wave breaks. The spray that a strong wind blows from the crest of a wave is also called sea foam. Foam also occurs when waves fall and water dissipates.

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

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

Rice. 1. Main parts of the wave

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

Rice. 1. Main characteristics of the wave

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

Under the influence of the Coriolis force, a water swell appears on the right side of the current, away from the mainland, and a depression is created near the land.

By origin waves are divided as follows:

friction waves;
pressure waves;
seismic waves or tsunamis;
seiches;
tidal waves.

Friction waves

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

Rice. 2. Wind waves and surf waves

Pyramidal, high and steep wind waves are called crowding. These waves are inherent in the central regions of cyclones. When the wind subsides, the excitement takes on a character swell, i.e., disturbances due to inertia.

The primary form of wind waves is ripple It occurs at a wind speed of less than 1 m/s, and at a speed greater than 1 m/s, first small and then larger waves are formed.

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

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

Pressure wave

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

Tsunami

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

Rice. 3. Tsunami transformation

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

The seismic belt of the Pacific Ocean is the main area for tsunami generation.

Seiches

Seiches are standing waves that arise in bays and inland seas. They occur by inertia after the cessation of external forces - wind, seismic shocks, sudden changes, intense precipitation, etc. In this case, in one place the water rises and in another it falls.

Tidal wave

Tidal waves- these are movements made under the influence of the tidal forces of the Moon and the Sun. Backlash sea water at high tide - low tide. The strip that drains during low tide is called drying.

There is a close connection between the height of the tides and the phases of the moon. New and full moons have the highest tides and lowest tides. They are called Syzygy. At this time, the lunar and solar tides, occurring simultaneously, overlap each other. In the intervals between them, on the first and last Thursdays of the Moon phases, the lowest, quadrature tides.

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

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

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

Sea currents

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

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

permanent, which pass in the same areas of the ocean, have the same general direction, more or less constant speed and stable physical and chemical properties transportable water masses (Northern and Southern trade winds, Gulf Stream, etc.);
periodic, in which direction, speed, temperature are subject to periodic patterns. They occur at regular intervals in a certain sequence (summer and winter monsoon currents in the northern Indian Ocean, tidal currents);
temporary, most often caused by winds.

By temperature sign sea currents are:

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

Based on the depth of their location in the water column, currents are distinguished:

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

By origin The following currents are distinguished:

friction, which may be drift or wind. Drift ones arise under the influence constant winds, and wind ones are created by seasonal winds;
gradient-gravitational, among which are stock, formed as a result of the tilting of the surface caused by excess water due to its influx from the ocean and heavy rainfall, and compensatory, which arise due to the outflow of water, scanty precipitation;
inert, which are observed after the cessation of the action of the factors that excite them (for example, tidal currents).

The ocean current system is determined by general circulation atmosphere.

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

Rice. 4. Cycles of sea currents

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

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

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

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

The most powerful and deepest surface currents play a critical role in the global circulation of the World Ocean. The most stable surface currents are the North and South Trade Winds of the Pacific and Atlantic Oceans and the South Trade Winds of the Indian Ocean. They have a direction from east to west. Tropical latitudes are characterized by warm waste currents, for example the Gulf Stream, Kuroshio, Brazilian, etc.

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

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

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

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

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

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

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

Wave(Wave, surge, sea) - formed due to the adhesion of particles of liquid and air; sliding along the smooth surface of the water, at first the air creates ripples, and only then, acting on its inclined surfaces, it gradually develops excitement water mass. Experience has shown that water particles do not have forward motion; moves only vertically. Sea waves are the movement of water on the sea surface that occurs at certain intervals.

The highest point of the wave is called comb or the top of the wave, and the lowest point is sole. Height of a wave is the distance from the crest to its base, and length this is the distance between two ridges or soles. The time between two crests or troughs is called period waves.

Main causes

On average, the height of a wave during a storm in the ocean reaches 7-8 meters, usually it can stretch in length - up to 150 meters and up to 250 meters during a storm.

In most cases, sea waves are formed by the wind. The strength and size of such waves depend on the strength of the wind, as well as its duration and “acceleration” - the length of the path along which the wind acts on the water surface. Sometimes the waves that hit the coast can originate thousands of kilometers from the coast. But there are many other factors in the occurrence of sea waves: these are the tidal forces of the Moon and the Sun, fluctuations in atmospheric pressure, eruptions of underwater volcanoes, underwater earthquakes, and the movement of sea vessels.

Waves observed in other water bodies can be of two types:

1) Wind created by the wind, taking on a steady character after the wind ceases to act and called established waves, or swell; Wind waves are created due to the influence of wind (movement air masses) to the surface of the water, that is, injection. The reason for the oscillatory movements of the waves becomes easy to understand if you notice the effect of the same wind on the surface of a wheat field. The inconstancy of wind flows, which create waves, is clearly visible.

2) Waves of movement, or standing waves, are formed as a result of strong tremors at the bottom during earthquakes or excited, for example, by a sharp change in atmospheric pressure. These waves are also called single waves.

Unlike tides and currents, waves do not move masses of water. The waves move, but the water remains in place. A boat that rocks on the waves does not float away with the wave. She will be able to move slightly along an inclined slope only thanks to the force of earth's gravity. Water particles in a wave move along rings. The further these rings are from the surface, the smaller they become and, finally, disappear completely. Being in a submarine at a depth of 70-80 meters, you will not feel the effect of sea waves even with the most strong storm on the surface.

Types of sea waves

Waves can travel great distances without changing shape and losing virtually no energy, long after the wind that caused them has died down. Breaking on the shore, sea waves release enormous energy accumulated during the journey. The force of continuously breaking waves changes the shape of the shore in different ways. The spreading and rolling waves wash the shore and are therefore called constructive. Waves crashing onto the shore gradually destroy it and wash away the beaches that protect it. That's why they are called destructive.

Low, wide, rounded waves away from the shore are called swells. Waves cause water particles to describe circles and rings. The size of the rings decreases with depth. As the wave approaches the sloping shore, the water particles in it describe increasingly flattened ovals. Approaching the shore, the sea waves can no longer close their ovals, and the wave breaks. In shallow water, the water particles can no longer close their ovals, and the wave breaks. Headlands are formed from harder rock and erode more slowly than adjacent sections of the coast. Steep, high sea waves undermine the rocky cliffs at the base, creating niches. Cliffs sometimes collapse. The terrace, smoothed by the waves, is all that remains of the rocks destroyed by the sea. Sometimes water rises along vertical cracks in the rock to the top and breaks out to the surface, forming a funnel. The destructive force of the waves widens the cracks in the rock, forming caves. When the waves wear away at the rock on both sides until they meet at a break, arches are formed. When the top of the arch falls into the sea, stone pillars remain. Their foundations are undermined and the pillars collapse, forming boulders. The pebbles and sand on the beach are the result of erosion.

Destructive waves gradually erode the coast and carry away sand and pebbles from sea beaches. Bringing the full weight of their water and washed-away material onto slopes and cliffs, the waves destroy their surface. They squeeze water and air into every crack, every crevice, often with explosive energy, gradually separating and weakening the rocks. The broken rock fragments are used for further destruction. Even the hardest rocks are gradually destroyed, and the land on the shore changes under the influence of waves. Waves can destroy the seashore with amazing speed. In Lincolnshire, England, erosion (destruction) is advancing at a rate of 2 m per year. Since 1870, when the largest lighthouse in the United States was built at Cape Hatteras, the sea has washed away beaches 426 m inland.

Tsunami

Tsunami These are waves of enormous destructive power. They are caused by underwater earthquakes or volcanic eruptions and can cross oceans faster than a jet plane: 1000 km/h. IN deep waters they can be less than one meter, but, approaching the shore, they slow down and grow to 30-50 meters before collapsing, flooding the shore and sweeping away everything in their path. 90% of all recorded tsunamis occurred in the Pacific Ocean.

The most common reasons.

About 80% of tsunami generation cases are underwater earthquakes. During an earthquake under water, a mutual vertical displacement of the bottom occurs: part of the bottom sinks, and part rises. Vertical oscillatory movements occur on the surface of the water, tending to return to the original level - the average sea level - and generates a series of waves. Not every underwater earthquake is accompanied by a tsunami. Tsunamigenic (that is, generating a tsunami wave) is usually an earthquake with a shallow source. The problem of recognizing the tsunamigenicity of an earthquake has not yet been solved, and warning services are guided by the magnitude of the earthquake. The most powerful tsunamis are generated in subduction zones. Also, it is necessary for the underwater shock to resonate with the wave oscillations.

Landslides. Tsunamis of this type occur more frequently than estimated in the 20th century (about 7% of all tsunamis). Often an earthquake causes a landslide and it also generates a wave. On July 9, 1958, an earthquake in Alaska caused a landslide in Lituya Bay. A mass of ice and earth rocks collapsed from a height of 1100 m. A wave was formed that reached a height of more than 524 m on the opposite shore of the bay. Cases of this kind are quite rare and are not considered as a standard. But underwater landslides occur much more often in river deltas, which are no less dangerous. An earthquake can cause a landslide and, for example, in Indonesia, where shelf sedimentation is very large, landslide tsunamis are especially dangerous, as they occur regularly, causing local waves more than 20 meters high.

Volcanic eruptions account for approximately 5% of all tsunami events. Large underwater eruptions have the same effect as earthquakes. In large volcanic explosions, not only are waves generated from the explosion, but water also fills the cavities of the erupted material or even the caldera, resulting in a long wave. A classic example is the tsunami generated after the eruption of Krakatoa in 1883. Huge tsunamis from the Krakatoa volcano were observed in harbors around the world and destroyed a total of more than 5,000 ships and killed about 36,000 people.

Signs of a tsunami.

Sudden fast the withdrawal of water from the shore over a considerable distance and the drying of the bottom. The further the sea recedes, the higher the tsunami waves can be. People who are on the shore and do not know about dangers, may stay out of curiosity or to collect fish and shells. In this case, it is necessary to leave the shore as soon as possible and move as far away from it as possible - this rule should be followed when, for example, in Japan, on the Indian Ocean coast of Indonesia, or Kamchatka. In the case of a teletsunami, the wave usually approaches without the water receding.
Earthquake. The epicenter of an earthquake is usually in the ocean. On the coast, the earthquake is usually much weaker, and often there is no earthquake at all. In tsunami-prone regions, there is a rule that if an earthquake is felt, it is better to move further from the coast and at the same time climb a hill, thus preparing in advance for the arrival of the wave.
Unusual drift ice and other floating objects, formation of cracks in fast ice.
Huge reverse faults at the edges of stationary ice and reefs, the formation of crowds and currents.

rogue waves

rogue waves(Roaming waves, monster waves, freak waves - anomalous waves) - giant waves that arise in the ocean, more than 30 meters high, have behavior unusual for sea waves.

Just 10-15 years ago, scientists considered sailors’ stories about gigantic killer waves that appear out of nowhere and sink ships as just maritime folklore. For a long time wandering waves were considered fiction, since they did not fit into any existing at that time mathematical models calculations of the occurrence and their behavior, because waves higher than 21 meters cannot exist in the oceans of planet Earth.

One of the first descriptions of a monster wave dates back to 1826. Its height was more than 25 meters and it was noticed in the Atlantic Ocean near the Bay of Biscay. Nobody believed this message. And in 1840, the navigator Dumont d'Urville risked appearing at a meeting of the French Geographical Society and declare that he saw a 35-meter wave with his own eyes. Those present laughed at him. But there were more and more stories about huge ghost waves that suddenly appeared in the middle of the ocean even during a small storm, and with their steepness resembled sheer walls of water.

Historical evidence of rogue waves

So, in 1933, the US Navy ship Ramapo was caught in a storm in the Pacific Ocean. For seven days the ship was tossed about by the waves. And on the morning of February 7, a shaft of incredible height suddenly crept up from behind. First, the ship was thrown into a deep abyss, and then lifted almost vertically onto a mountain of foaming water. The crew, who were lucky enough to survive, recorded a wave height of 34 meters. It moved at a speed of 23 m/sec, or 85 km/h. So far, this is considered the highest rogue wave ever measured.

During World War II, in 1942, the Queen Mary liner carried 16 thousand American military personnel from New York to the UK (by the way, a record for the number of people transported on one ship). Suddenly a 28-meter wave appeared. “The upper deck was at its usual height, and suddenly - suddenly! - it suddenly went down,” recalled Dr. Norval Carter, who was on board the ill-fated ship. The ship tilted at an angle of 53 degrees - if the angle had been even three degrees more, death would have been inevitable. The story of "Queen Mary" formed the basis of the Hollywood film "Poseidon".

However, on January 1, 1995, oil platform"Dropner" in the North Sea off the coast of Norway, a wave of 25.6 meters high, called the Dropner wave, was first recorded by instruments. The Maximum Wave project allowed us to take a fresh look at the causes of the death of dry cargo ships that transported containers and other important cargo. Further research recorded over three weeks around the globe more than 10 single giant waves, the height of which exceeded 20 meters. New project received the name Wave Atlas, which provides for the compilation of a worldwide map of observed monster waves and its subsequent processing and addition.

Causes

There are several hypotheses about the causes of extreme waves. Many of them lack common sense. Most simple explanations based on the analysis of a simple superposition of waves different lengths. Estimates, however, show that the probability of extreme waves in such a scheme is too small. Another noteworthy hypothesis suggests the possibility of focusing wave energy in some surface current structures. These structures, however, are too specific for an energy focusing mechanism to explain the systematic occurrence of extreme waves. The most reliable explanation for the occurrence of extreme waves should be based on the internal mechanisms of nonlinear surface waves without involving external factors.

Interestingly, such waves can be both crests and troughs, which is confirmed by eyewitnesses. Further research involves the effects of nonlinearity in wind waves, which can lead to the formation of small groups of waves (packets) or individual waves (solitons) that can travel long distances without significantly changing their structure. Similar packages have also been observed many times in practice. Characteristic Features Such groups of waves, confirming this theory, are that they move independently of other waves and have a small width (less than 1 km), and the heights drop off sharply at the edges.

However, it has not yet been possible to completely clarify the nature of the anomalous waves.

The formation of waves on the surface of water is called disturbance.

Waves observed on the surface of water are divided into:

Friction waves:
- wind, formed as a result of the action of wind
- deep

Tidal waves.

Gravitational waves:
- gravitational waves in shallow water
- gravitational waves in deep water
- seismic waves (tsunamis) that arise in the oceans as a result of an earthquake (or volcanic activity) and reach a height of 10-30 m off the coast.
- ship waves

Waves consist of alternating swells and troughs. The top of the wave is called the crest, and the base of the wave is called the trough.
In coastal areas of the sea, only wind waves (friction waves) are significant.

Wind waves arise with the wind; when the wind stops, these waves in the form of a dead swell, gradually fading, continue to move in the same direction. Wind waves depend on the size of the water space open for wave acceleration, wind speed and time of action in one direction, as well as depth. As the depth decreases, the wave becomes steeper.
Wind waves are asymmetrical, their windward slope is gentle, their leeward slope is steep. Since the wind acts more strongly on the upper part of the wave than on the lower part, the wave crest crumbles, forming “lambs”. In the open sea, "lamblets" are formed in a wind that is called "fresh" (wind force 5 and a speed of 8.0-10.7 m/s, or 33 km/h).
Swell- excitement that continues after the wind has already died down, weakened or changed direction. A disturbance that spreads by inertia in complete calm is called a dead swell.
When waves from different directions meet in a certain area, a crush. The chaotic accumulation of waves formed when direct waves meet reflected ones is also crush.
When waves pass over banks, reefs and rocks, breakers.
The approach of waves onto the shore with an increase in height and steepness and subsequent capsizing is called surf.

The surf gets different character depending on which shore: shallow (having small angles of inclination and a large width of the underwater slope) or deep (having significant slopes of the underwater slope).

The overturning of the crest of a moving wave onto a steep bank forms reverse faults having great destructive power.

© Yuri Danilevsky: November storm. Sevastopol

When the surf occurs near a deep shore that rises steeply from the water, the wave breaks up only when it hits the shore. In this case, a reverse wave is formed, meeting the next one and reducing its impact force, and then a new wave comes in and hits the shore again.
Such wave impacts in case of large swell or strong excitement are often accompanied by surges of waves to a considerable height.

© Storm in Sevastopol, November 11, 2007

On the shores of the Black Sea, the wave impact force can reach 25 tons per 1 m 2.
When upturning, the wave gains enormous force. On the Shetland Islands, north of Scotland, there are fragments of gneiss rocks weighing up to 6-13 tons, thrown by the surf to a height of 20 m above sea level.

The rapid movement of waves and swell onto the shore is called roll forward.

Waves are regular when their crests are clearly visible, and irregular when the waves do not have clearly defined crests and are formed without any visible pattern.
Wave crests perpendicular to the wind direction in the open sea, lake, reservoir, but near the shore they take a position parallel to the coastline, running onto the banks.
The direction of wave propagation in the open sea is indicated on the surface of the water by a family of parallel stripes of foam - the traces of collapsing wave crests.