What controls the ebb and flow. The largest amplitudes of tides. The influence of the moon on tide
What is ebb and flow
On many sea coasts, you can observe how the water level evenly drops at regular intervals and only sticky soil remains. This process is called ebb. However, after a few hours the water level rises again and the soil on the shore is again covered with water. This process is called tide. The water level changes regularly twice a day.
When the ebb tide gives way
Ebb and flow regularly replace each other: ebb tide is followed by ebb tide, followed by the next ebb tide. Highest level water in the sea or ocean at high tide is called full water, and the minimum at low tide is called low water, respectively. The cycle "high water - low tide - low water - high tide - high water" is 12 hours 25 minutes. This means that the ebb and flow can be observed twice a day.
How does the ebb and flow occur
The gravitational force of the Moon determines the formation of the first tidal ridge in the sea on the side of the Earth facing it. Due to the laws of physics associated with the rotation of the Earth and the emergence of centrifugal force, a second tidal ridge is formed on the opposite side of the Earth, even more powerful than the first. Therefore, the water level rises here too.
Between these two ridges, it descends, and there is an ebb tide! And the Sun, by the force of its attraction, affects the Earth, as well as the ebb and flow. But the force of the influence of the Sun is much less than that of the Moon, although the mass of the Sun is 30 million times the mass of the Moon. The reason for this lies in the fact that the Sun is 390 times farther from the Earth than the Moon is from the Earth.
First tidal hydroelectric power plant
The ebb and flow, that is, the rise and fall of the sea level, generates a lot of energy. It can be used to generate electricity. The first and largest currently tidal hydroelectric power plant in the world was built in the estuary (narrow bay of the mouth) of the Ranet River (Saint-Malo, France) and was commissioned in 1966. There the difference between ebb and flow is very large (amplitude 8.5 meters).
What other factors affect the ebb and flow
In addition to the forces of gravity, cosmic bodies, the Moon and the Sun, other factors affect the ebb and flow: the rotation of the Earth slows down the tides, the shores do not allow water to rise. In addition, the ebb and flow of the tide is affected by severe storms, which hinder the outflow of seawater from the coast. Therefore, its level in such places is much higher than at a normal tide. The ebb and flow of the tide is also affected by the force of the wind: if it blows from the shore, the water level drops significantly below normal.
Is the ebb and flow always visible
They say that in some seas, for example in the Mediterranean or Baltic, there is no ebb and flow. Of course, this is not the case, because they are found in all seas. However, in the Mediterranean and Baltic Seas, the difference between full and low water (the amplitude of high and low tide) is so insignificant that it is practically invisible. In the North Sea, on the other hand, the ebb and flow are very clearly distinguished.
Tidal waves arise in the oceans and pass into the marginal seas. If the marginal sea is connected to the ocean only by a narrow strait, such as the Mediterranean Sea, the tidal waves either do not reach it or are very weak. The North Sea is connected with the Atlantic Ocean by a wide strait, so the tidal waves easily reach the coast and the tide in this place is perfectly visible.
What is syzygy tide
Particularly strong ebb and flow can be observed during 14 days, when the Moon and the Sun during the full moon and new moon (syzygy) are in line with the Earth. At this time, the tidal forces of both celestial bodies, acting in the same direction, add up and intensify the tide. The so-called syzygy tide begins when the high water rises most high. Accordingly, at low tide, the water drops to the lowest level.
What is the amplitude of ebb and flow
The difference between high and low tide during high tide and low tide is called the amplitude. In this case, the forces of attraction of the Sun and the Moon play a role: when they strengthen each other, the amplitude increases (syzygy tide), and when the forces of attraction weaken, the amplitude, on the contrary, decreases (quadrature tide). In the open sea, the amplitude of the tide does not exceed 50 centimeters. On the banks, on the other hand, it is much larger.
So, on the coast of the North Sea of Germany, for example, it is 2-3 meters, on the English coast of the North Sea - up to 8 meters, and in the Bay of Saint-Malo (France) in the English Channel - up to 11 meters. This can be explained by the fact that in shallow waters, tidal waves, like all others, lose speed and slow down, as a result of which the water level rises.
What is Quadrature Tide
For seven days after the full moon and new moon, the Sun, Earth and Moon are no longer on the same straight line. When the tidal forces of the Moon and the Sun interact at right angles to each other, a quadrature tide begins: the full water rises slightly, and the low water level practically does not fall.
What are tidal currents
Tides not only cause water levels to rise and fall. As the sea rises and falls, the water moves back and forth. In the open sea, this is hardly noticeable, but in straits and bays, where the movement of water is limited, tidal currents can be observed. In the first case (tidal current) it is directed towards the coast, in the second (ebb current) - in the opposite direction. Specialists usually call the change of tidal currents a turn. At the moment of turning, the water is in a calm state, and this phenomenon is called the "blind spot" of the tide.
Where are the greatest amplitudes of ebb and flow
The Bay of Fundy, on the east coast of Canada, is home to some of the largest high and low tide amplitudes on the planet. This means that the difference between high and low water at high and low tide is here the maximum. With a syzygy tide, it reaches 21 meters. Previously, fishermen installed nets in high water, and collected fish from them during low water: unusual way fishing!
How a storm tide occurs
A stormy tide is called a tide when the water rolls onto the coast especially high. It arises from strong winds that blow towards land and come with the syzygy tide. Let us remind you: during it, full water rises especially high, and low water drops especially low. This occurs during the full moon and new moon periods.
The strength of the winds and their duration lead to a storm tide when the water rises more than a meter above the mid-tide point. Distinguish between a strong storm tide, in which the water rises by 2.5 meters, and super strong - when the water rises by more than 3 meters.
What speed can tidal currents reach?
Deep in the oceans, tidal currents reach speeds of about a kilometer per hour. In narrow straits, it can be 15 to 20 kilometers per hour.
The oceans live by their own rules, which are harmoniously combined with the laws of the universe. For a long time, people noticed that they were actively moving, but they could not understand in any way what these fluctuations in sea level were connected with. Let's find out what is high tide, low tide?
Ebb and flow: mysteries of the ocean
The sailors knew very well that the ebb and flow is a daily occurrence. But the nature of these changes could not be understood either by ordinary residents or by scientists. As early as the fifth century BC, philosophers tried to describe and characterize how the oceans moved. seemed to be something fantastic and extraordinary. Even respected scientists considered the tides to be the breath of the planet. This version has existed for several millennia. Only at the end of the seventeenth century, the meaning of the word "tide" was associated with the movement of the moon. But it was not possible to explain this process from a scientific point of view. Hundreds of years later, scientists figured out this riddle and gave precise definition daily changes in water level. The science of oceanology, which appeared in the twentieth century, established that the tide is the rise and fall of the water level of the World Ocean in connection with the gravitational influence of the Moon.
Are the tides the same everywhere?
The influence of the moon on the earth's crust is not the same, so it cannot be said that the tides around the world are identical. In some parts of the world, daily sea level drops reach sixteen meters. And the inhabitants of the Black Sea coast practically do not notice the ebb and flow, since they are the smallest in the world.
Usually the change occurs twice a day - in the morning and in the evening. But in the South China Sea, the tide is the movement of water masses that occurs only once every twenty-four hours. Most of all, sea level changes are noticeable in straits or other narrow places. If you observe, then with the naked eye it will be noticeable how quickly the water leaves or comes. Sometimes it rises five meters in a few minutes.
As we have already found out, the change in sea level is caused by the impact on the earth's crust of its permanent satellite, the Moon. But how does this process take place? To understand what a tide is, it is necessary to understand in detail the interaction of all the planets in the solar system.
The moon and the earth are in constant dependence on each other. The Earth attracts its satellite, and that, in turn, seeks to attract our planet. This endless rivalry allows you to maintain the required distance between two space bodies. The moon and the earth move in their orbits, then moving away, then approaching each other.
At that moment, when the Moon comes closer to our planet, the earth's crust bends towards it. This causes the excitement of the water on the surface of the earth's crust, as if it seeks to rise higher. The receding of the earth's satellite causes a decline in the level of the World Ocean.
The interval of ebb and flow on Earth
Since the tide is a regular phenomenon, it must have its own certain interval of movement. Oceanologists were able to calculate exact time lunar days... It is customary to call this term the rotation of the Moon around our planet, it is slightly longer than the twenty-four hours we are accustomed to. Every day the ebb and flow of the tide is shifted by fifty minutes. This time interval is necessary for the wave to "catch up" with the Moon, which moves thirteen degrees over the earth's day.
Impact of ocean tides on rivers
We have already figured out what a tide is, but few people know about the influence of these oceanic fluctuations on our planet. Surprisingly, even rivers are affected by ocean tides, and sometimes the result of this intervention is incredibly frightening.
During heavy tides, a wave entering the mouth of a river meets a stream of fresh water. As a result of mixing water masses of different densities, a powerful shaft is formed, which begins to move at a tremendous speed against the flow of the river. This stream is called boron, and it is capable of destroying almost all living things on its way. A similar phenomenon in a matter of minutes, it washes away coastal settlements and erodes the coastline. Bohr stops as suddenly as it started.
Scientists have recorded cases when a powerful forest turned rivers back or completely stopped them. It is not hard to imagine how disastrous these phenomenal tidal events have become for all the inhabitants of the river.
How do tides affect marine life?
Not surprisingly, tides have a huge impact on all organisms that live in the depths of the ocean. The hardest part is for small animals living in coastal zones... They are forced to constantly adapt to changing water levels. For many of them, tides are a way to change their habitat. During high tides, small crustaceans move closer to the coast and find food for themselves, the tidal wave pulls them deeper into the ocean.
Oceanologists have proven that many marine life are closely associated with tidal waves. For example, in some species of whales, their metabolism slows down during low tides. In other deep-sea inhabitants, reproductive activity depends on the wave height and its amplitude.
Most scientists believe that the disappearance of such phenomena as fluctuations in the level of the World Ocean will lead to the extinction of many living things. Indeed, in this case, they will lose their power source and will not be able to adjust their biological clock to a certain rhythm.
The Earth's Rotation Speed: Is the Influence of the Tides Great?
For many decades, scientists have been studying everything related to the term "tide". This is a process that brings more and more riddles every year. Many experts associate the speed of the Earth's rotation with the action of tidal waves. According to this theory, under the influence of tides are formed On their way, they constantly overcome the resistance of the earth's crust. As a result, almost imperceptibly for humans, the planet's rotation speed slows down.
By studying sea corals, oceanologists have found that a few billion years ago, the earth's day was twenty-two hours. In the future, the Earth's rotation will slow down even more, and at some point it will simply equal the amplitude of the lunar day. In this case, as scientists predict, the ebb and flow will simply disappear.
Human life activity and the amplitude of oscillations of the World Ocean
It is not surprising that a person is also susceptible to the action of hot flashes. After all, it is 80% liquid and cannot but respond to the influence of the moon. But man would not have been the crown of nature's creation if he had not learned to use practically everything for himself. natural phenomena.
The energy of the tidal wave is incredibly high, so they have been creating for many years various projects for the construction of power plants in areas with large amplitude movement of water masses. There are already several such power plants in Russia. The first was built in the White Sea and was an experimental version. The power of this station did not exceed eight hundred kilowatts. Now this figure seems ridiculous, and new power plants using the tidal wave are generating energy that powers many cities.
Scientists see these projects as the future of the Russian energy industry, because they allow them to treat nature more carefully and cooperate with it.
The ebb and flow are natural phenomena that not so long ago were completely unexplored. Each new discovery by oceanologists leads to even greater questions in this area. But perhaps someday scientists will be able to unravel all the secrets that the ocean tide presents to mankind every day.
The surface level of the oceans and seas changes periodically, approximately twice a day. These fluctuations are called ebb and flow. During high tide, the ocean level gradually rises and reaches its highest position. At low tide, the level gradually drops to the lowest. At high tide, water flows to the coast, at low tide - from the coast.
The ebb and flow is standing. They are formed due to the influence of such cosmic bodies as the Sun. According to the laws of interaction of cosmic bodies, our planet and the Moon mutually attract each other. The lunar attraction is so great that the surface of the ocean, as it were, bends towards it. The moon moves around the Earth, and a tidal wave "runs" along the ocean after it. When the wave reaches the shore, the tide is coming. A little time will pass, the water after the Moon will move away from the coast - that is the low tide. According to the same universal cosmic laws, ebb and flow are formed from the attraction of the Sun. However, the tidal force of the Sun, due to its remoteness, is much less than the lunar one, and if there was no Moon, then the tides on Earth would be 2.17 times less. The explanation of tidal forces was first given by Newton.
Tides vary in duration and magnitude. Most often, there are two high tides and two low tides during the day. On the arcs and coasts of East and Central America, there is one high tide and one low tide during the day.
The magnitude of the tides is even more varied than their period. Theoretically, one lunar tide is 0.53 m, solar - 0.24 m.Thus, the largest tide should have a height of 0.77 m.In the open ocean and near the islands, the tide value is quite close to the theoretical one: in the Hawaiian Islands - 1 m , on the island of Saint Helena - 1.1 m; on the islands - 1.7 m.On the continents, the value of tides ranges from 1.5 to 2 m.In the inland seas, the tides are very insignificant: - 13 cm, - 4.8 cm.It is considered tide-free, but around Venice the tides are up to 1 m. The largest can be noted the following tides registered in:
In the Bay of Fundy (), the tide has reached a height of 16-17 m. This is the highest tide in the entire globe.
In the north, in the Penzhinskaya Bay, the tide height reached 12-14 m. This is the highest tide off the coast of Russia. However, the above tide rates are the exception rather than the rule. In the overwhelming majority of tide measurement points, they are small and rarely exceed 2 m.
The importance of tides is very great for maritime navigation and the construction of ports. Each tidal wave carries a huge amount of energy.
The seas and oceans leave the coast twice a day (low tide) and approach it twice (high tide). In some bodies of water, there are practically no tides, while in others the difference between ebb and flow along the coastline can be up to 16 meters. Basically, the tides are semi-daily (twice a day), but in some places they are daily, that is, the water level changes only once a day (one low tide and one tide).
The ebb and flow are most noticeable in the coastal strips, but in fact they pass through the entire thickness of the oceans and other bodies of water. In straits and other narrow places, low tides can reach very high speeds - up to 15 km / h. Basically, the phenomenon of ebb and flow is influenced by the Moon, but to some extent the Sun is also involved in this. The Moon is much closer to the Earth than the Sun, therefore its influence on the planets is stronger even though the natural satellite is much smaller, and both celestial bodies revolve around the star.
The influence of the moon on tides
If the continents and islands did not interfere with the influence of the Moon on the water, and the entire surface of the Earth was covered by an ocean of equal depth, then the tides would look like this. The area of the ocean, closest to the Moon, due to the force of gravity, would rise towards the natural satellite, due to the centrifugal force, the opposite part of the reservoir would also rise, it would be a tide. A drop in the water level would occur in a line that is perpendicular to the strip of influence of the Moon, in that part there would be an ebb.
The sun can also have some effect on the world's oceans. On a new moon and a full moon, when the Moon and the Sun are in a straight line with the Earth, the attractive force of both luminaries adds up, thereby causing the strongest ebb and flow. If these celestial bodies are perpendicular to each other with respect to the Earth, then the two forces of attraction will oppose each other, and the tides will be the weakest, but still in favor of the Moon.
The presence of different islands brings great variety to the movement of waters at ebb and flow. In some reservoirs, the channel and natural obstacles in the form of land (islands) play an important role, therefore water flows in and out unevenly. The waters change their position not only in accordance with the gravity of the moon, but also depending on the terrain. In this case, when the water level changes, it will flow along the path of least resistance, but in accordance with the influence of the night star.
The phases of the moon are different and not quite so it is all connected. The ebb and flow of the phenomenon of daily frequency. The phases of the moon are a phenomenon with a frequency of 29.5 days in the lunar month.
The phases of the moon are how the Earth, illuminated by the Sun, casts a shadow onto the Moon. The moon revolves around the Earth, the relative position of the Moon, Earth and the Sun changes, and the shadow on the Moon from the Earth also changes.
Imagine two balls. They are connected by a barbell. The large ball rotates on its axis. And that little ball on the other end of the bar rotates around the big ball. The barbell is an image of the force of gravity between the Earth and the Moon. In the place where the bar is fixed, tidal disturbances are obtained.
If the Earth did NOT rotate around its axis, then the hump of the tide would go along the Earth's surface behind the Moon, which revolves around the Earth with a period of ~ 27 days (why not 29.5 - a separate question - google the difference between the sidereal and synodic months).
But we also have the rotation of the Earth around its axis.
That is, returning to the image of the connecting rod. In the case of the Earth and the Moon, the bar is rigidly fixed on the Moon, that is, the Moon is facing the Earth with one side (only slightly "sways"), but on the Earth the bar is not fixed, but moves along the surface. The earth rotates on its axis with a period of 24 hours.
Those. the tidal hump runs no longer with a period of ~ 27 days, but with a period of 24 hours.
But we need to clarify. In fact, the ebb and flow, just for simplicity, are explained by the Moon alone, but in fact:
Also, one of the reasons for the occurrence of ebb and flow is the daily (proper) rotation of the Earth. The masses of water in the world ocean, which have the shape of an ellipsoid, the major axis of which does not coincide with the axis of rotation of the Earth, participate in its rotation around this axis. This leads to the fact that in the frame of reference associated with the earth's surface, the ocean runs along the reciprocal opposite sides the globe, two waves, leading at each point of the ocean coast to periodic, twice a day, recurring low tide phenomena, alternating with high tides.
The most interesting thing, notice (last sentence), is the tide in one hemisphere and the tide in the opposite one. Those. the watery shell is like an ellipsoid, not like a pear.
Over time, we formed a double question and in it you can read more about how an ellipsoid is obtained instead of a pear. See comments on the answer.
It is also important to say about the influence of the sun on tides using the example of syzygy and quadrature tides. Sometimes the sun, moon and earth line up (earth<--луна<--солнце) и силы притяжения солнца и луны - складываются, соответственно самые сильные приливы - сизигийные. Они происходят во время новолуния и полнолуния. Квадратурные приливы - самые слабые,когда силы тяготения луны и солнца находятся под прямым углом и частично нейтрализуют друг друга. Они происходят, когда луна находится в фазе первой четверти и последней четверти. Также можно почитать о приливах здесь astro-site.narod.ru/zemlimsiz.html
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