How are waves formed? Why do waves form in the sea? How do waves form in the sea.

How are waves formed? Surf reports and wave forecasts are compiled from scientific research and weather modeling. In order to find out what waves will form in the near future, it is important to understand how they are formed.

The main cause of wave formation is wind. The waves best suited for surfing are formed by the interaction of winds above the ocean surface, away from the shore. The action of wind is the first stage of wave formation.

Winds blowing offshore in a particular area can also cause waves, but they can also lead to deterioration in the quality of breaking waves.

It has been found that winds blowing from the sea tend to produce unstable and uneven waves as they affect the direction of wave travel. The winds blowing from the coast serve, in a certain sense, as a kind of balancing force. The wave travels many kilometers from the depths of the ocean to the shore, and the wind from land has a “braking” effect on the face of the wave, allowing it to avoid breaking longer.

Low pressure areas = good waves for surfing

In theory, areas of low pressure promote the formation of nice, powerful waves. In the depths of such areas, wind speeds are higher and wind gusts form more waves. The friction created by these winds helps create powerful waves that travel thousands of kilometers until they hit their final obstacles, the coastal areas where people live.

If winds generated in areas of low pressure continue to blow on the ocean surface for a long time, the waves become more intense as energy accumulates in all the resulting waves. In addition, if winds from areas of low pressure affect a very large area of ​​​​the ocean, then all the resulting waves concentrate even more energy and power, which leads to the formation of even larger waves.

From ocean waves to surf waves: the seabed and other obstacles

We have already analyzed how disturbances in the sea and the waves generated by them are formed, but after “birth” such waves still have to travel a huge distance to the shore. The waves that originated in the ocean have to do a long way before they reach land.

During their journey, before surfers even get on them, these waves will have to overcome other obstacles. The height of the emerging wave does not match the height of the waves the surfers are riding.

As waves move through the ocean, they are exposed to irregularities in the seabed. As gigantic moving masses of water overcome high spots on the seafloor, the total amount of energy concentrated in the waves changes.

For example, continental shelves far from the coast offer resistance to moving waves due to the force of friction, and by the time the waves reach coastal waters, where the depth is shallow, they have already lost their energy, strength and power.

When waves move through deep waters without encountering obstacles on their way, they usually hit the coastline with enormous force. The depths of the ocean floor and their changes over time are studied through bathymetric studies.

Using the depth map, it is easy to find the deepest and shallowest waters of the oceans of our planet. Studying the topography of the seabed is of great importance for preventing shipwrecks and cruise liners.

In addition, studying the structure of the bottom can provide valuable information for predicting the surf at a particular surf spot. When waves reach shallow water, their speed usually decreases. Despite this, the wavelength shortens and the crest increases, resulting in an increase in wave height.

Sandbanks and wave crest increase

Sandbanks, for example, always change the nature of beach breaks. This is why the quality of waves changes over time, for better or worse. Sandy irregularities on the ocean floor allow the formation of distinct, concentrated wave crests from which surfers can begin their slide.

When a wave encounters a new sandbar, it will typically form a new crest, since such an obstacle causes the crest to rise, that is, the formation of a wave suitable for surfing. Other obstacles to waves include groins, sunken vessels, or simply natural or artificial reefs.

Waves are generated by the wind and as they travel are influenced by the topography of the seabed, precipitation, tides, rip currents off the coast, local winds and bottom irregularities. All these weather and geological factors contribute to the formation of waves suitable for surfing, kitesurfing, windsurfing and boogie surfing.

Wave forecasting: theoretical foundations

• Long-period waves tend to be larger and more powerful.
• Waves with a short period tend to be smaller and weaker.
• The wave period is the time between the formation of two clearly defined crests.
• Wave frequency is the number of waves passing through a certain point in a certain time.
• Big waves move fast.
• Small waves move slowly.
• Intense waves form in areas of low pressure.
• Low pressure areas are characterized by rainy and cloudy weather.
• Areas of high pressure are characterized by warm weather and clear skies.
• Larger waves form in deep coastal areas.
• Tsunamis are not suitable for surfing.

The science of waves originated during the preparations for the Allied landings in Normandy in 1944. For many millennia - since our unknown prehistoric ancestor first went to sea on his fragile boat - people have suffered from the waves: they are tossed around, rocked, they die in the waves. The Argonauts, the Vikings, Columbus, the Pilgrim Fathers, millions of travelers looked at the waves with obvious hostility. They knew the effect of the waves, but did not know their nature.

At the Klebec Conference, which decided on the Normandy landings, someone asked: “How do waves work?” It was important to get an answer, because for the landing they were going to build artificial harbors and jetties, as well as lay a pipeline across the English Channel. Storm or calm, a huge expeditionary force had to be landed with precision down to the second.

No one could give an answer - not the sailors of the Allied navy, nor scientists. They, of course, knew about tidal phenomena. Newton gave a scientific explanation of the forces of the Moon, and in reference books they could find an accurate prediction of the tide level at any point on the Normandy coast. But no one thought about the nature of the waves - the sailors tolerated their evil temper without asking any questions.

Thus, scientists had to think twice. With the exception of the mechanism of wave formation, all other conditions were known: the nature of the English Channel, this peculiar “funnel”, the configuration of its coastline, which was greedily destroyed by the waves, and even the geology of the seashore. Then the long-haired English professor (even having put on a military uniform, he kept his hairstyle) remembered how, while swimming on this coast after a stormy night, he noticed peat in the surf. Did this have anything to do with the problem of wave formation? Of course, it did, and a detachment of paratroopers immediately received instructions to go on a raid to collect geological samples in the area of ​​a possible landing.

More or less detailed information was collected about the nature of the excitement in the places of the proposed landing. Subsequent events showed that this information was not entirely reliable. It was necessary scientific research waves that previously more often attracted the attention of poets and artists than scientists.

Scientists are currently trying to figure out why wind energy creates the orderly waves of a strong storm, rather than just chaos in the ocean. But further research is required here. Storm centers, or areas where “main waves” form, are known, but there are other wave systems due to secondary causes. The visible waves that we observe at any given time are the result of the superposition of several groups of waves propagating in different directions at different speeds.

They need to be “sorted”. This is done using a wave analyzer, which tells how the energy is distributed between different wavelengths. The analyzer is an electronic device that selects sea waves, just like a radio receiver selects electromagnetic waves. It "catches" waves originating in different areas, like radio waves emitted by different transmitters, and separates them.

It is known that waves of various lengths, emerging from a storm area, spread so that very long low waves, rising like hills on shallow banks, announce the approach of a shorter and steeper dead swell, which carries most of the energy. Such a level of precision has now been achieved that scientists on the coasts of Cornwall and California can measure the very low swell that brought wave energy from the roaring forties of the southern hemisphere.

Methods have been developed that can tell the difference between what sailors call “swell” and “dead swell.” It must be said that the instruments can tell the difference between waves created by local winds and waves that may originate thousands of kilometers away. Thus, oceanographers, in collaboration with meteorologists, can predict waves based on meteorological data.

Through experimental and theoretical research, scientists can produce tables and diagrams that are of extraordinary value to coastal and port engineers and naval architects. Much data has already been obtained on the impact of waves on the sea coast and shallows, which is of great importance for work to protect coastlines that have been destroyed by waves for centuries.

This is the case on the surface of the ocean, where gigantic 20-meter-high swells toss the huge liner around like a tiny skiff. But what happens in the depths? Oceans cover about three-quarters of the surface of the globe, and we know perhaps less about the geography of this flooded part of our world than about the surface of the Moon. The average depth of the ocean is about four kilometers, but there are depressions, or trenches, up to more than 10 kilometers, much “higher” than Everest. And this is not a “world of silence.” Hydrophones can detect noises, often made by creatures we have never seen. And this world, of course, is not calm, it is in continuous movement.

Seas and climate are inseparable. The oceans act like a giant accumulator, a “savings bank” for heat. Water is “stored” solar heat and releases it in cold weather, so that there is a continuous regulation of the world's oceans. To know the weather, you need to know the sea, and, conversely, to know the ocean, you need to find out the process of atmospheric circulation.

It is estimated that nine-tenths of surface currents (not just waves) are driven by wind - including the Gulf Stream, whose movement was studied by Benjamin Franklin (yes, the one depicted on the hundred dollar bill) about two centuries ago, the Humboldt Current, which carried the Kon-Tiki raft to Polynesia, and the Kuroshio current. And even deep currents are to some extent influenced by the wind, since the surface water pushed towards the shore is directed downward, creating water on the deep layers and forcing them to move in the form of a current.

The study of deep currents brings us more and more new information. It must be remembered that water in the oceans has unequal densities and that lighter water can lie on top of heavier water due to great salinity or coldness - like a layer cake. These layers can either slide over one another or move in different directions relative to each other.

Various instruments have been created to study the nature and movement of these deep currents. In some respects they are similar to the instruments used by meteorologists. When meteorologists want to probe the upper atmosphere and study air currents high above the ground, they launch balloons - called "radiosondes" - with transmitting equipment that transmits information by radio. Oceanographers who want to study currents at great depths use something similar.

They use two long aluminum tubes that contain batteries and simple electronic circuitry. The circuit has a sound source similar to that used in echo sounding. This device can be immersed to a certain specified depth. If you load it at the surface so that it floats at a depth of 2500 meters, then only one gram of additional weight will be required to sink the device to exactly a depth of 2530 meters. At a certain depth, it drifts with the current and sends signals upward. These signals can be received by the ship on the surface. Such methods were used by the joint Anglo-American expedition to study the Gulf Stream.

The northerly direction of the Gulf Stream has been shown to be very strong at the surface. However, in the layer of water between depths of 1350 and 1800 meters, movement is either very weak or completely absent. The floats, immersed to even greater depths - 2460 and 2760 meters - drifted south, in the direction opposite to the surface current. The speed of this countercurrent was about 0.6 kilometers per hour.

Currently, there are more attempts to penetrate the “secrets of the sea”: researchers have already visited the “world of silence”, a bathyscaphe has descended to the bottom of one of the Pacific depressions, ships on the surface are conducting regular observations. And gradually we begin to learn about phenomena hitherto unknown.

P.S. And finally, it is worth noting that even if you have purchased the best fins for swimming, we still recommend that you refrain from swimming in a strong storm, when the waves are especially high.

Initially, a wave appears due to the wind. A storm formed in the open ocean, far from the coast, will create winds that will begin to affect the surface of the water and therefore a swell will begin to appear. The wind, its direction, as well as speed, all this data can be seen on weather forecast maps. The wind begins to blow up the water, and “Small” (capillary) waves will begin to appear, initially they begin to move in the direction in which the wind is blowing.

The wind blows on a flat surface of water, the longer and stronger the wind begins to blow, the greater the impact on the surface of the water. Over time, the waves connect and the size of the wave begins to increase. The constant wind begins to form a large swell. The wind has a much greater impact on already created waves, although not large ones, much more than on the calm surface of the water.

The size of the waves directly depends on the speed of the blowing wind that forms them. Wind blowing at a constant speed can generate a wave of comparable size. And as soon as the wave acquires the size that the wind put into it, it becomes a fully formed wave that goes towards the shore.

Waves have different speeds and periods. Waves with a long period move quite quickly and cover greater distances than their counterparts with a lower speed. As they move away from the source of the wind, the waves combine to form a swell, which goes towards the coast. Waves that are no longer affected by the wind are called “Bottom waves.” These are the waves that all surfers hunt for.

What affects the size of a swell? There are three factors that influence the size of waves in the open ocean:
Wind speed – The higher the speed, the larger the resulting wave will be.
Duration of the wind - the longer the wind blows, similar to the previous factor - the wave will be larger.
Fetch (wind coverage area) – The larger the coverage area, the larger the wave produced.
When the wind stops influencing the waves, they begin to lose their energy. They will continue to move until they hit the protrusions of the bottom near some large oceanic island and the surfer will catch one of these waves in case of successful coincidences.

There are factors that influence the size of waves in a particular location. Among them:
The direction of the swell is what will allow the waves to come to the place we need.
Ocean floor - A swell moving from the open ocean encounters an underwater ridge of rocks, or a reef - forms large waves that can curl into a pipe. Or a shallow protrusion of the bottom will, on the contrary, slow down the waves and they will waste some of their energy.
Tidal cycle - many surf spots are directly affected by this phenomenon.

Sea waves mean a form of periodic, continuously changing movement in which water particles oscillate around their equilibrium position.

Sea waves are classified according to various criteria:

By origin The following types of waves are distinguished:

Wind, formed under the influence of wind,

Tidal waves, which arise under the influence of the attraction of the Moon and the Sun,

Anemobaric, formed when the sea surface level deviates from the equilibrium position, occurring under the influence of wind and changes in atmospheric pressure,

Seismic (tsunamis) resulting from underwater earthquakes and eruptions of underwater or coastal volcanoes,

Ship damage, formed during the movement of the vessel.

According to the forces tending to return the water particle to the equilibrium position:

Capillary waves (ripples),

Gravitational.

According to the action of force after the formation of a wave:

Free (the force has ceased),

Forced (the action of force has not stopped.

According to the variability of elements over time:

Steady (do not change their elements),

Unsteady, developing, fading, (changing their elements over time).

By location in the water column:

Superficial, arising on the surface of the sea ,

Internal, arising at depth.

By form:

Two-dimensional, representing long parallel shafts following each other,

Three-dimensional, not forming parallel shafts. The length of the crest is commensurate with the wavelength (wind waves),

Solitary (single), having only a dome-shaped crest without a wave base.

According to the ratio of wavelength and sea depth:

Short (wavelength is significantly less than the depth of the sea),

Long (the wavelength is much greater than the depth of the sea).

By moving the waveform:

Translational, characterized by visible movement of the wave profile. Water particles move in circular orbits.

Standing (seiche), do not move in space. Water particles move only in the vertical direction. Seiches occur when the water level rises at one edge of a reservoir and simultaneously falls at the other, usually after the wind stops.

In small basins (harbours, bays, etc.), a seiche can occur when ships pass.

Most often in the seas and oceans, navigators have to encounter wind waves, which cause the ship to rock, flood the deck, reduce the speed, and in a strong storm cause damage that leads to the death of the ship.

Wind waves are divided into three main types:

Vetrovoe - this is the excitement that is formed by the wind blowing in this place At the moment. When the wind weakens or completely stops, the waves turn into swells.

Swell is a wave that propagates by inertia in the form of free waves after the wind weakens or stops. A swell that spreads during calm conditions is called dead. Swell waves are usually longer than wind waves, flatter and have an almost symmetrical shape. The direction of the swell may differ from the direction of the wind and often the swell propagates towards the wind or at right angles to it.

Surf - These are waves formed by wind waves or swells near the coast. Propagating from the deep water of the open sea towards the shore in shallow water, the waves are transformed. Three-dimensional waves turn into two-dimensional ones, having the form of long crests parallel to each other. Their height, steepness and destructive force increase. The impact force of a breaking wave can reach 90 t/m2. In the surf zone, capsizing and turning over moments occur, which are dangerous for watercraft.

Therefore, swimming in the shallow coastal zone and landing on the shore here is very difficult, dangerous, and sometimes impossible.

Warnings about underwater obstacles can be breakers.

A breaker is a phenomenon where waves overturn and break over shoals, banks, reefs and other rises in the bottom.

One type of wave is crowd - This is the meeting of waves from different directions, as a result of which they lose a certain direction of movement and represent random standing waves.

Oscillations that propagate through space over time are called waves. The wave process is not accompanied by mass transfer, but only by energy transfer. That is, water particles oscillating vertically do not move horizontally, only their energy changes

Waves can be different - on the surface of a liquid, sound, electromagnetic. But now we will focus on the waves that arise in the sea. As is clear from the definition, waves arise when certain generated vibrations begin to propagate in space. And for these same vibrations to occur, the action of an external force is necessary. Depending on what external force causes the occurrence of oscillations (and therefore waves), friction waves, pressure waves, seismic, standing and tidal waves are distinguished.

Friction waves include wind waves and internal ones. Wind waves arise at the air-water interface. When the wind blows, layers of air periodically impact the surface of the water and cause it to oscillate. The vibrations spread in space and waves travel across the sea. Usually their height is no more than four meters, but in the case of stormy winds it increases to fifteen meters and higher. Greatest height waves can reach up to 25 meters in the westerly wind zone of the Southern Hemisphere.

The appearance of waves on the surface of the sea is preceded by ripples. It occurs when the wind speed is less than one meter per second. As speed increases, the size of the waves increases. High and steep wind waves have the figurative name of crush. When the wind subsides, the waves continue for some time due to inertia, in this case they say that there is a swell in the sea. A wave traveling through shallow water to the shore is called a surf. Significant masses of water are involved in this process, even when the wave height is not very high. When it reaches shallow coastal waters, water particles due to of great importance energy, begin to move horizontally, back and forth, carrying stones and sand with them. Anyone who has swum in the sea knows how these pebbles hit your feet. The surf is strong enough to drag huge boulders.

Internal waves

Internal waves (underwater) arise under the surface of the sea, at the boundary of two layers of water with different properties. Captain Nemo was not entirely accurate and overly idealized the ocean when he claimed that peace reigns within it. The water column of the ocean is heterogeneous; it consists of different layers. Their physical characteristics (temperature, salinity, density) change unevenly from layer to layer, and internal waves are formed at the boundary between them. They were first discovered by the Norwegian polar explorer, doctor of zoology, founder of physical oceanography Fridtjof Wedel-Jarlsberg Nansen (1861 - 1930). While sailing on the ship "Fram" on North Pole, Nansen observed periodic changes in the temperature and salinity of sea water at the same depth in the Arctic Ocean.

Such waves can occur near river mouths, in straits with two-layer currents, and at the edge of melting ice. The height of internal waves can be tens of times higher than the height of waves on the surface, but they are inferior in speed to surface waves. These waves pose a danger to submarines, erode port structures (breakwaters, landing stages, piers), and are capable of dispersing sound waves. Such waves are clearly visible from a satellite (pictured). They are usually small, but in the Luzon Strait, between the Philippines and Taiwan, they reach a height of 170 meters. This is explained by the characteristics of water flows and bottom topography.

Pressure waves arise due to rapid changes in atmospheric pressure in places where cyclones pass. These are single waves that can travel hundreds, or even thousands of kilometers from their point of origin and suddenly rush ashore, washing away everything in their path. So in September 1935, a pressure wave nine meters high hit the coast of Florida and carried away 400 human lives. The formation of such waves is not uncommon on the coasts of India, China, and Japan.

Seismic waves arise as a result of active processes in the bowels of the Earth - earthquakes, eruptions of underwater volcanoes, the formation of cracks and faults in earth's crust on the ocean floor. As a result, specific waves are formed, low in the open ocean and growing to colossal sizes when approaching the shore - tsunami. Typically, the harbinger of the appearance of such an anomalous wave is a sharp retreat of the sea several kilometers from the coast. This is a danger signal - the sea will return in the form of a maddening foaming monster, bringing death and destruction. However, there is a separate article about tsunami on our website and we will be glad if you refer to it.

Tidal waves

As a result of the action of gravitational forces on the water shell of the Earth from the Sun and Moon, tidal waves are formed. These waves are most often small, in the open ocean their height is up to two meters. It increases near the coast. The maximum tide height reaches on the Atlantic coast of North America - up to 18 meters. In our Sea of ​​Okhotsk - almost 13 meters. The strongest impact is observed during the new moon and full moon, when the gravitational attractions of the Sun and Moon add up. At this time, the tides are at their highest and the tides are at their lowest.

In inland seas, the tidal wave is completely insignificant; in the Baltic Sea near St. Petersburg its height is five centimeters. But in some rivers its movement presents a wonderful picture. For example, in the Amazon (pictured), when a tidal wave moves against the current and its height reaches five meters. This phenomenon is felt at a distance of 1,400 kilometers from the mouth.

Standing waves (seiches) appear as a result of the interference (addition) of waves arising under the influence of external forces (wind, pressure) and waves reflected from shore ledges or underwater obstacles of sufficient length.

Seiches

Such waves grow in height, alternating between crests and troughs, and remain in place, rising and falling. They can be easily simulated in a bathtub if you perform vertical oscillatory movements on the surface of the water, for example, periodically lowering the cover from the bathtub drain hole into the water. After some time, pointed shafts correctly distributed in time and space will be established, standing in one place. This is the object of our research.

Seiches appear in unexpected places, where there seem to be no reflected waves, since the obstacles are not visible, they are located under the surface of the water. They can cause the death of sea vessels. In particular, such a version exists for the mysterious and terrible region Bermuda Triangle, as one of the possible explanations for the disappearance of the ships. This place is generally considered difficult for navigation due to various factors - the presence of shallow ledges, the confluence of several sea currents with different water temperatures, and complex bottom topography. Here the continental shelf first gradually deepens, and then suddenly goes to a decent depth. The underwater topography of the region influences the formation of a standing wave. It occurs in clear, windless weather and is therefore doubly insidious. A modern multi-ton ship lifted by such a wave will split into pieces under the influence of its own gravity and disappear from the surface in a matter of minutes.

Sea waves are one of the most fascinating natural phenomena. Their endless variety and eternal movement calms and energizes. It is not for nothing that the peoples of ancient civilizations were aware of the healing properties of thalassotherapy (sea healing). The salt composition of human blood is close to the composition of sea water, this element is related to us, and in the rustling of the surf on the shore one can feel the beating of a large and kind heart.

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