Wave formation theory: learning to understand forecasts. What do we know about the waves of the sea Where do the waves on the sea come from

In this article we will talk about where the waves come from and what they are. After all, waves are a unique natural phenomenon that gives surfers a lot of emotions and sensations, forcing them to give up a lot. Surfing is waves. And good surfing is impossible without knowing how waves are born, what affects their speed, strength and shape, as well as without understanding that each wave is different from the other.

Where do ocean waves come from

It's all about the swell. If not for the swell, there would be no waves. What is a swell? Swell is the energy of the wind transferred to the waves. There are several types of swells, wind and bottom (groundswell, reel):

1. As the name suggests, a wind swell is formed due to the wind. Such a swell occurs when the wind blows right next to the coast (for example, during a storm) and creates a chop (chaotic unrest on the surface of the ocean). The wind swell is not very suitable for surfing.
2. Swell, due to which surf waves form on the ocean coast, is called bottom swell. This is exactly where the waves that interest surfers come from.

How a swell is born

Far away in the ocean, a storm is raging with strong winds. These winds start a wave on the water. The stronger the wind, the larger the wave. A certain wind speed corresponds to a very specific wave size. It works like a sail and allows the wind to disperse itself and do more.

When the waves reach their maximum possible sizes, they begin to travel to the far shores in the direction where the wind blows. After a while, the waves become similar to each other - the larger ones absorb the small ones, and the fast ones eat the slow ones. The resulting group of waves, approximately the same size and the same power, is called a swell. A swell can travel hundreds or even thousands of kilometers before it reaches the coastline.

As the swell approaches shallower depths, the lower water flows collide with the bottom, slow down and have nowhere to go but move up, pushing all the water above them. When the water can no longer support its own weight, it begins to collapse. Actually, that's where the waves come from, on which you can surf.

1. Closeouts (close-out) are closed along the entire length in whole sections. Not the best option for skiing unless you are learning to ski in foam. When the size of the waves is more than 2 meters, then such waves can be dangerous. Closeouts can be recognized by the width of the wave peak, which can reach several meters.
2. Spilling waves they slowly approach the shore and, thanks to the slight slope of the bottom, slowly begin to break, without forming a sharp wall and pipe. Such waves need to be paddled in advance, and are more suitable for beginner surfers and longboarders.
3. Plunging waves. Fast, powerful, sharp waves that form a tube. Occurs when a swell encounters an obstacle in its path. For example, it may be a protruding reef or a stone slab. We are used to seeing such waves in surf photos and surf videos. They allow you to make passages in the pipe and airs (jumps). Dangerous for beginner surfers.

Types of surf spots

The nature of the wave is determined by the place where it rises, which place is called the surf spot. Surf spots are divided into several types.

1. Beach break: the swell comes to the beach with a sandy bottom and the wave, having collided with the alluvium of sand at the bottom, begins to break. The peculiarity of beach breaks is that the peaks rise in places where sand alluvium is formed, and their shape and position can change every day, depending on the wind, underwater currents, tide movements and other factors.
   With a change in the shape and size of the alluvium, the characteristics of the waves also change, that is, the waves can be either sharp trumpeting or gentle. The sandy bottom is not particularly dangerous, so beach breaks are great for learning to surf. In Bali, beach breaks are the entire beach along Kuta, Legian and Seminyak, as well as Brava Beach, Eco Beach and others.
2. Reef break.This type of surf spot is characterized by the presence of a reef at the bottom. As a reef, both coral reefs and a stone bottom in the form of individual stones or whole slabs can act. The shape, power and wavelength depend on the shape of the reef at the bottom of the ocean. On a spot with a reef break, you can always predict where the wave will peak. Reef breaks are much more dangerous than beach breaks due to sharp reefs and rocks on the bottom.In Bali, most of the surf spots are reef breaks. Uluwatu, Balangan, Padang-Padang, Batu Bolong and many others.
3. Point break- is when the vell collides with some kind of barrier protruding from the shore. It can be a stone ridge, a cape, a small peninsula. After the collision, the waves go around this obstacle and begin to break one after another. In such places, waves of the most correct form rise, go one after another, and can give you very, very long passages.An example of a point break in Bali is the Medewi spot.

Wind and water

In addition to location and swell, where the waves come from for surfing is also affected by the wind and the height of the water (tides).

Where do waves come from for riding or "gone with the wind"
The quality of the waves depends on the wind on the shore. The most correct wind for surfing is its absence. That is why surfers get up at 4 am or earlier to get to the spot before dawn, when the wind has not had time to wake up, and the water is still mirror-smooth (glassy).

If the wind is still blowing, then the waves will not be spoiled (and sometimes even better) if it is directed from the coast to the ocean. This wind is called offshore. Offshore keeps the waves from breaking, making them sharper.

The wind that blows from the ocean to the shore is called onshore. He breaks the waves, forcing them to close ahead of time, blowing off the peaks. The least preferred wind of all. A strong onshore can generally kill the entire gurney.

Also, the wind can blow along the coast, it is called crossshore. Here much depends on its strength and direction. Sometimes a crossshore can slightly spoil the waves, and sometimes it can act as negatively as an onshore.

Ebb and flow
About tides and how they affect waves, you can read in this article.

wave anatomy

In the structure of the wave, several elements are distinguished:
Wall (face/wall) The section of the wave where the surfer spends most of his time.
Lip (lip)- falling crest of a wave.
shoulder- a place where the wave gradually disappears.
Outsole (trough)- the bottom of the wave.
Pipe (tube/barrel)- a place where water surrounds the surfer from all sides.

Now you know where the waves come from, but theory is theory, and you can truly know the waves only in the process of surfing. The more you watch the waves and ride them, the better you will read the ocean, and this will allow you to catch more and more great waves. And now the board under the armpit and run to ride! 🙂

It seems to be a banal question, but there are some interesting nuances.

Waves arise for various reasons: due to the wind, the passage of a ship, the fall of an object into the water, the attraction of the moon, an earthquake, an eruption of an underwater volcano or a landslide. But if they are caused by liquid displacement from a passing ship or a falling object, the attraction of the Moon and the Sun contributes to the appearance of tidal waves, and an earthquake can cause a tsunami, it is more difficult with wind.

Here's how it goes...

Here the matter is in the movement of air - there are chaotic whirlwinds in it, small at the surface and large in the distance. When they pass over a reservoir, the pressure decreases, and a bulge forms on its surface. The wind begins to push harder on its windward slope, which leads to a pressure difference, and because of it, the air movement begins to "pump" energy into the wave. In this case, the speed of the wave is proportional to its length, that is, the longer the length, the greater the speed. Wave height and wave length are related. Therefore, when the wind accelerates the wave, its speed increases, therefore, the length and height increase. True, the closer the wave speed is to the wind speed, the less energy the wind can give to the wave. If their speeds are equal, the wind does not transfer energy to the wave at all.

Now let's look at how waves form in general. Two physical mechanisms are responsible for their formation: gravity and surface tension. When some of the water rises, gravity tries to bring it back, and when it goes down, it displaces neighboring particles, which also try to come back. The force of surface tension does not care which way the surface of the liquid is bent, it acts in any case. As a result, water particles oscillate like a pendulum. Neighboring areas are “infected” from them, and a surface traveling wave arises.

Wave energy is well transmitted only in the direction in which the particles can move freely. It is easier to do this on the surface than at depth. This is because the air does not create any restrictions, while at a depth the water particles are in very cramped conditions. The reason is poor compressibility. Because of it, the waves can travel long distances on the surface, but decay very quickly in depth.

It is important that during the wave the fluid particles almost do not move. At great depths, the trajectory of their movement has the shape of a circle, at shallow depths - an elongated horizontal ellipse. Thanks to this, ships in the harbor, birds or pieces of wood sway on the waves without actually moving on the surface.

A special type of surface waves are the so-called killer waves - giant solitary waves. Why they occur is still unknown. They are rare in nature and cannot be simulated in the laboratory. However, most scientists believe that killer waves are formed due to a sharp decrease in pressure over the surface of the sea or ocean. But a more thorough study of them lies ahead.

Here we are in detail

Initially, the 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, in connection with this, a swell begins to occur. Wind, its direction, as well as speed, all these data can be seen on weather forecast maps. The wind begins to inflate the water, and "Small" (capillary) waves will begin to appear, initially they begin to move in the direction in which the wind blows.

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

The size of the waves directly depends on the speed of the blowing wind that forms them. A 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 coast.

Waves have different speeds and periods. Waves with a long period move fast enough and cover greater distances than their counterparts with a lower speed. As you move away from the source of the wind, the waves combine to form a swell that 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 affect the size of waves in the open ocean:
Wind speed - The higher the speed, the larger the wave will eventually be.
Wind duration - the longer the wind blows, similarly to the previous factor, the wave will be larger.
Fetch (wind coverage area) - The larger the coverage area, the larger the wave.
When the effect of the wind on the waves stops, they begin to lose their energy. They will keep moving until they hit the ledges of the bottom near some large oceanic island and the surfer catches one of these waves in case of good luck.

There are factors that affect the size of the 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 bumps into an underwater ridge of rocks, or a reef - forms large waves with which they can twist into a pipe. Or a shallow ledge of the bottom - on the contrary, it will slow down the waves and they will spend part of their energy.
The tidal cycle - many surf spots are directly dependent on this phenomenon.

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

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

The main causes of occurrence

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 waves that break on 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 tide-forming forces of the Moon, the Sun, fluctuations in atmospheric pressure, eruptions of underwater volcanoes, underwater earthquakes, and the movement of ships.

Waves observed in other water spaces can be of two kinds:

1) wind, created by the wind, taking on the cessation of the action of the wind, a steady character and called steady waves, or swell; Wind waves are created due to the effect of wind (movement of air masses) on the surface of the water, that is, injection. The reason for the oscillatory movements of the waves becomes easily understood if one notices the effect of the same wind on the surface of a wheat field. The inconsistency of wind flows, which create waves, is clearly visible.

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

Unlike tides, tides and currents, waves do not move masses of water. The waves are coming, but the water stays where it is. A boat that rocks on the waves does not float with the wave. It will be able to move a little on an inclined, only thanks to the force of the earth's gravity. The water particles in the wave move along the rings. The farther these rings are from the surface, the smaller they become and, finally, disappear altogether. Being in a submarine at a depth of 70-80 meters, you will not feel the effect of sea waves even during the strongest storm on the surface.

Types of sea waves

Waves can travel vast distances without changing shape and losing little or no energy, long after the wind that caused them has died down. Breaking on the shore, sea waves release huge energy accumulated during the journey. The force of continuously breaking waves changes the shape of the shore in different ways. Overflowing and rolling waves wash the shore and therefore are called constructive. Waves crashing on the coast gradually destroy it and wash away the beaches that protect it. Therefore they are called destructive.

Low, wide, rounded waves away from the shore are called swell. Waves make water particles describe circles, rings. The size of the rings decreases with depth. As the wave approaches the sloping shore, the water particles in it describe more and more flattened ovals. Approaching the shore, the sea waves can no longer close their ovals, and the wave breaks. In shallow water, water particles can no longer close their ovals, and the wave breaks. Capes are formed from harder rock and are destroyed more slowly than neighboring sections of the coast. Steep, high sea waves undermine the rocky cliffs at the base, forming 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 expands the cracks in the rock, forming caves. When the waves undermine the rock from two sides until they join in a gap, arches form. When the top of the arch falls into the sea, stone pillars remain. Their bases are undermined, and the pillars collapse, forming boulders. The pebbles and sand on the beach are the result of erosion.

Destructive waves gradually wash away the coast and carry away sand and pebbles from sea beaches. Bringing down the entire weight of their water and washed-away material on the slopes and cliffs, the waves destroy their surface. They force water and air into every crack, every crevice, often with the energy of an explosion, gradually parting and weakening the rocks. Breakaway rock fragments are used for further destruction. Even the hardest rocks are gradually destroyed, and the land on the coast is changed by the action of the 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 the 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 as they approach the shore, they slow down their run and grow to 30-50 meters before collapsing, flooding the shore and sweeping away everything in their path. 90% of all recorded tsunamis occur in the Pacific Ocean.

The most common reasons.

About 80% of tsunami generations are underwater earthquakes. During an earthquake under water, a mutual displacement of the bottom occurs along the vertical: part of the bottom falls, and part rises. On the surface of the water, oscillatory movements occur along the vertical, trying to return to the initial level - the mean 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 strongest tsunamis are generated in subduction zones. Also, it is necessary that the underwater push entered into resonance with wave oscillations.

Landslides. Tsunamis of this type occur more frequently than was 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, as a result of an earthquake in Alaska, a landslide occurred in Lituya Bay. A mass of ice and terrestrial rocks collapsed from a height of 1100 m. A wave formed, reaching a height of more than 524 m on the opposite shore of the bay. Such cases are quite rare and are not considered as a standard. But much more often underwater landslides occur 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 with a height of more than 20 meters.

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

Signs of a tsunami.

• sudden fast withdrawal of water from the shore for a considerable distance and 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 danger, may stay out of curiosity or to collect fish and shells. In this case, it is necessary to leave the coast as soon as possible and move away from it to the maximum distance - this rule should be followed, for example, while in Japan, on the Indian Ocean coast of Indonesia, 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 none 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 a wave.
• unusual drift ice and other floating objects, the formation of cracks in the fast ice.
• Huge reverses at the edges of immovable ice and reefs, the formation of crowds, currents.

killer waves

killer waves(Wandering waves, monster waves, freak wave - an anomalous wave) - giant waves that occur in the ocean, more than 30 meters high, have behavior unusual for sea waves.

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

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 ventured to appear at a meeting of the French Geographical Society and declare that he had seen a 35-meter wave with his own eyes. storm, and their steepness resembled sheer walls of water, it became more and more.

Historical evidence of "killer waves"

So, in 1933, the USS Ramapo was caught in a storm in the Pacific Ocean. For seven days the ship was thrown over the waves. And on the morning of February 7, a shaft of incredible height suddenly crept up from behind. At 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. She moved at a speed of 23 m / s, or 85 km / h. So far, this is considered the highest rogue wave ever measured.

During the Second World War, in 1942, the Queen Mary liner carried 16,000 American troops from New York to Great Britain (by the way, a record for the number of people transported on one ship). Suddenly there was a 28-meter wave. "The upper deck was at its usual height, and suddenly - once! - she abruptly went down," recalled Dr. Norval Carter, who was on board the ill-fated ship. The ship banked at an angle of 53 degrees - if the angle had been at least 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, a wave 25.6 meters high, called the Dropner wave, was first recorded on the Dropner oil platform in the North Sea off the coast of Norway. The "Maximum Wave" project made it possible to take a fresh look at the causes of the death of dry cargo ships that carried containers and other important cargo. Further research recorded more than 10 single giant waves around the globe in three weeks, the height of which exceeded 20 meters. The new project was called Wave Atlas (Atlas of waves), which provides for the compilation of a world 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. The simplest explanations are based on the analysis of a simple superposition of waves of different lengths. Estimates, however, show that the probability of extreme waves in such a scheme turns out to be too small. Another noteworthy hypothesis suggests the possibility of wave energy focusing in some structures of surface currents. These structures, however, are too specific for the mechanism of energy focusing 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 significant changes in their structure. Similar packages have also been repeatedly observed in practice. The characteristic features of such groups of waves, confirming this theory, is that they move independently of other waves and have a small width (less than 1 km), with heights dropping sharply at the edges.

However, it has not yet been possible to fully elucidate the nature of anomalous waves.

The wind itself can be seen on weather forecast maps: these are low pressure zones. The greater their concentration, the stronger the wind will be. Small (capillary) waves initially move in the direction the wind is blowing.

The stronger and longer the wind blows, the greater its effect on the surface of the water. Over time, the waves begin to increase in size.

The wind has a greater effect on small waves than on a calm surface of the water.

The size of a wave depends on the speed of the wind that forms it. Wind blowing at some constant speed will be able to generate a wave of comparable size. And once a wave reaches the size that the wind can put into it, it becomes "fully formed."

The generated waves have different wave speeds and periods. (More details in the article) Waves with a long period move faster and cover greater distances than their slower counterparts. As they move away from the wind source (propagation), the waves form lines of swells, which inevitably roll onto the shore. Most likely, you are familiar with the concept of a set of waves!

Waves that are no longer affected by the wind are called ground waves (ground swell)? This is exactly what surfers are looking for!

What affects the size of a swell?

There are three main factors that affect the size of waves on the high seas.
Wind speed The larger it is, the larger the wave will be.
wind duration- similar to the previous one.
Fetch(wind coverage area) - again, the larger the coverage area, the larger the wave is formed.

As soon as the influence of the wind on them stops, the waves begin to lose their energy. They will move until the moment when the protrusions of the seabed or other obstacles in their path (a large island for example) absorb all the energy.

There are several factors that affect the size of a wave at a particular location. Among them:

Swell direction- will it allow the swell to get to the place we need?
ocean floor- Swell, moving from the depths of the ocean to the underwater ridge of rocks, forms large waves with barrels inside. A shallow ledge opposite will slow down the waves and cause them to lose energy.
Tidal cycle- some sports are completely dependent on it.

Find out how the best waves come about.