October 15th, 2012
British photographer Michael Marten created a series of original photographs capturing the coast of Britain from the same angles, but at different times. One shot at high tide and one at low tide.
It turned out to be quite unusual, and positive reviews of the project literally forced the author to start publishing the book. The book, called "Sea Change", was published in August this year and was released in two languages. It took Michael Marten about eight years to create his impressive series of photographs. The time between high and low water averages just over six hours. Therefore, Michael has to linger in each place for longer than just the time of a few shutter clicks. The author had been nurturing the idea of creating a series of such works for a long time. He was looking for how to realize changes in nature on film, without human influence. And I found it by chance, in one of the coastal Scottish villages, where I spent the whole day and caught the time of high and low tide.
Periodic fluctuations in water levels (rises and falls) in water areas on Earth are called tides.
The highest water level observed in a day or half a day during high tide is called high water, the lowest level during low tide is called low water, and the moment of reaching these maximum level marks is called the standing (or stage) of high tide or low tide, respectively. Intermediate level sea - a conditional value, above which the level marks are located during high tides, and below - during low tides. This is the result of averaging large series of urgent observations.
Vertical fluctuations in water level during high and low tides are associated with horizontal movements of water masses in relation to the shore. These processes are complicated by wind surge, river runoff and other factors. Horizontal movements of water masses in the coastal zone are called tidal (or tidal) currents, while vertical fluctuations in water levels are called ebbs and flows. All phenomena associated with ebbs and flows are characterized by periodicity. Tidal currents periodically change direction to the opposite direction, unlike ocean currents, moving continuously and unidirectionally, are caused by the general circulation of the atmosphere and cover large areas of the open ocean.
High and low tides alternate cyclically in accordance with changing astronomical, hydrological and meteorological conditions. The sequence of tidal phases is determined by two maxima and two minima in the daily cycle.
Although the Sun plays a significant role in tidal processes, the decisive factor in their development is the force gravitational attraction Moons. The degree of influence of tidal forces on each particle of water, regardless of its location on the earth's surface, is determined by the law universal gravity Newton.
This law states that two material particles attract each other with a force directly proportional to the product of the masses of both particles and inversely proportional to the square of the distance between them. It is understood that the greater the mass of the bodies, the greater the force of mutual attraction that arises between them (with the same density, a smaller body will create less attraction than a larger one).
The law also means that the greater the distance between two bodies, the less attraction between them. Since this force is inversely proportional to the square of the distance between two bodies, the distance factor plays a much larger role in determining the magnitude of the tidal force than the masses of the bodies.
The gravitational attraction of the Earth, acting on the Moon and keeping it in near-Earth orbit, is opposite to the force of attraction of the Earth by the Moon, which tends to move the Earth towards the Moon and “lifts” all objects located on the Earth in the direction of the Moon.
The point on the earth's surface located directly below the Moon is only 6,400 km from the center of the Earth and on average 386,063 km from the center of the Moon. In addition, the mass of the Earth is 81.3 times the mass of the Moon. Thus, at this point on the earth’s surface, the Earth’s gravity acting on any object is approximately 300 thousand times greater than the Moon’s gravity.
It is a common idea that water on Earth directly below the Moon rises in the direction of the Moon, causing water to flow away from other places on the Earth's surface, but since the Moon's gravity is so small compared to the Earth's, it would not be enough to lift so much water. huge weight.
However, the oceans, seas and large lakes on Earth, being large liquid bodies, are free to move under the influence of lateral forces, and any slight tendency to move horizontally sets them in motion. All waters that are not directly under the Moon are subject to the action of the component of the Moon's gravitational force directed tangentially (tangentially) to the earth's surface, as well as its component directed outward, and are subject to horizontal displacement relative to the solid earth's crust.
As a result, water flows from adjacent areas of the earth's surface towards a place located under the Moon. The resulting accumulation of water at a point under the Moon forms a tide there. The actual tidal wave in open ocean has a height of only 30-60 cm, but it increases significantly when approaching the shores of continents or islands.
Due to the movement of water from neighboring areas towards a point under the Moon, corresponding ebbs of water occur at two other points removed from it at a distance equal to a quarter of the Earth’s circumference. It is interesting to note that the decrease in sea level at these two points is accompanied by a rise in sea level not only on the side of the Earth facing the Moon, but also on opposite side.
This fact is also explained by Newton's law. Two or more objects located at different distances from the same source of gravity and, therefore, subjected to the acceleration of gravity of different magnitudes, move relative to each other, since the object closest to the center of gravity is most strongly attracted to it.
Water at the sublunar point experiences a stronger pull towards the Moon than the Earth below it, but the Earth in turn has a stronger pull towards the Moon than water on the opposite side of the planet. Thus, a tidal wave arises, which on the side of the Earth facing the Moon is called direct, and on the opposite side - reverse. The first of them is only 5% higher than the second.
Due to the rotation of the Moon in its orbit around the Earth, approximately 12 hours and 25 minutes pass between two successive high tides or two low tides in a given location. The interval between the climaxes of successive high and low tides is approx. 6 hours 12 minutes The period of 24 hours 50 minutes between two successive tides is called a tidal (or lunar) day.
Tide inequalities. Tidal processes are very complex and many factors must be taken into account to understand them. In any case, the main features will be determined:
1) the stage of development of the tide relative to the passage of the Moon;
2) tidal amplitude and
3) the type of tidal fluctuations, or the shape of the water level curve.
Numerous variations in the direction and magnitude of tidal forces give rise to differences in the magnitude of morning and evening tides in a given port, as well as between the same tides in different ports. These differences are called tide inequalities.
Semi-diurnal effect. Usually within a day, due to the main tidal force - the rotation of the Earth around its axis - two complete tidal cycles are formed.
When viewed from the North Pole of the ecliptic, it is obvious that the Moon rotates around the Earth in the same direction in which the Earth rotates around its axis - counterclockwise. At each next revolution given point the earth's surface again takes a position directly under the Moon somewhat later than during the previous revolution. For this reason, both the ebb and flow of the tides are delayed by approximately 50 minutes every day. This value is called lunar delay.
Half-month inequality. This main type of variation is characterized by a periodicity of approximately 143/4 days, which is associated with the rotation of the Moon around the Earth and its passage through successive phases, in particular syzygies (new moons and full moons), i.e. moments when the Sun, Earth and Moon are located on the same straight line.
So far we have touched only on the tidal influence of the Moon. The gravitational field of the Sun also affects the tides, however, although the mass of the Sun is much greater than the mass of the Moon, the distance from the Earth to the Sun is so greater than the distance to the Moon that the tidal force of the Sun is less than half that of the Moon.
However, when the Sun and Moon are on the same straight line, either on the same side of the Earth or on opposite sides (during the new moon or full moon), their gravitational forces add up, acting along the same axis, and the solar tide overlaps with the lunar tide.
Likewise, the attraction of the Sun increases the ebb caused by the influence of the Moon. As a result, the tides become higher and the tides lower than if they were caused by the Moon's gravity alone. Such tides are called spring tides.
When the gravitational force vectors of the Sun and the Moon are mutually perpendicular (during quadratures, i.e. when the Moon is in the first or last quarter), their tidal forces oppose, since the tide caused by the attraction of the Sun is superimposed on the ebb caused by the Moon.
Under such conditions, the tides are not as high and the tides are not as low as if they were due only to the gravitational force of the Moon. Such intermediate ebbs and flows are called quadrature.
The range of high and low water marks in this case is reduced by approximately three times compared to the spring tide.
Lunar parallactic inequality. The period of fluctuations in tidal heights, which occurs due to lunar parallax, is 271/2 days. The reason for this inequality is the change in the distance of the Moon from the Earth during the latter’s rotation. Due to the elliptical shape of the lunar orbit, the tidal force of the Moon at perigee is 40% higher than at apogee.
Daily inequality. The period of this inequality is 24 hours 50 minutes. The reasons for its occurrence are the rotation of the Earth around its axis and a change in the declination of the Moon. When the Moon is near the celestial equator, the two high tides on a given day (as well as the two low tides) differ slightly, and the heights of morning and evening high and low waters are very close. However, as the Moon's north or south declination increases, morning and evening tides of the same type differ in height, and when the Moon reaches its greatest north or south declination, this difference is greatest.
Tropical tides are also known, so called because the Moon is almost above the Northern or Southern tropics.
The diurnal inequality does not significantly affect the heights of two successive low tides in the Atlantic Ocean, and even its effect on the heights of the tides is small compared to the overall amplitude of the fluctuations. However, in the Pacific Ocean, diurnal variability is three times greater in low tide levels than in high tide levels.
Semiannual inequality. Its cause is the rotation of the Earth around the Sun and the corresponding change in the declination of the Sun. Twice a year for several days during the equinoxes, the Sun is near the celestial equator, i.e. its declination is close to 0. The Moon is also located near the celestial equator for approximately one day every half month. Thus, during the equinoxes, there are periods when the declinations of both the Sun and the Moon are approximately equal to 0. The total tidal effect of the attraction of these two bodies at such moments is most noticeable in areas located near the earth's equator. If at the same time the Moon is in the new moon or full moon phase, the so-called. equinoctial spring tides.
Solar parallax inequality. The period of manifestation of this inequality is one year. Its cause is the change in the distance from the Earth to the Sun during the orbital movement of the Earth. Once for each revolution around the Earth, the Moon is at its shortest distance from it at perigee. Once a year, around January 2, the Earth, moving in its orbit, also reaches the point of closest approach to the Sun (perihelion). When these two moments of closest approach coincide, causing the greatest total tidal force, we can expect more high levels tides and more low levels low tides Likewise, if the passage of aphelion coincides with apogee, lower tides and shallower tides occur.
Greatest tidal amplitudes. The world's highest tide is generated by strong currents in Minas Bay in the Bay of Fundy. Tidal fluctuations here are characterized by a normal course with a semi-diurnal period. The water level at high tide often rises by more than 12 m in six hours, and then drops by the same amount over the next six hours. When the effect of spring tide, the position of the Moon at perigee and the maximum declination of the Moon occur on the same day, the tide level can reach 15 m. This exceptionally large amplitude of tidal fluctuations is partly due to the funnel-shaped shape of the Bay of Fundy, where the depths decrease and the shores move closer together towards top of the bay. The causes of tides, which have been the subject of constant study for many centuries, are among those problems that have given rise to many controversial theories even in relatively recent times
Charles Darwin wrote in 1911: “There is no need to look for ancient literature for the sake of grotesque theories of tides.” However, sailors manage to measure their height and take advantage of the tides without having any idea of the actual causes of their occurrence.
I think that we don’t have to worry too much about the causes of the tides. Based on long-term observations for any point in the land's water area, special tables which indicate the times of high and low water for each day. I’m planning my trip, for example, to Egypt, which is famous for its shallow lagoons, but try to plan in advance so that the full water falls in the first half of the day, which will allow you to fully ride during most of the daylight hours.
Another question related to tides that is interesting for kiters is the relationship between wind and water level fluctuations.
A folk superstition states that at high tide the wind intensifies, but at low tide it turns sour.
The influence of wind on tidal phenomena is more understandable. The wind from the sea pushes the water towards the coast, the height of the tide increases above normal, and at low tide the water level also exceeds the average. On the contrary, when the wind blows from land, water is driven away from the coast, and sea level drops.
The second mechanism operates by increasing atmospheric pressure over a vast area of water; the water level decreases as the superimposed weight of the atmosphere is added. When atmospheric pressure increases by 25 mm Hg. Art., the water level drops by approximately 33 cm. Zone high pressure or anticyclone is usually called good weather, but not for kiters. There is calm in the center of the anticyclone. A decrease in atmospheric pressure causes a corresponding increase in water levels. Consequently, a sharp drop in atmospheric pressure combined with hurricane-force winds can cause a noticeable rise in water levels. Such waves, although called tidal, are in fact not associated with the influence of tidal forces and do not have the periodicity characteristic of tidal phenomena.
But it is quite possible that low tides can also influence the wind, for example, a decrease in the water level in coastal lagoons leads to greater warming of the water, and as a consequence to a decrease in the temperature difference between the cold sea and the heated land, which weakens the breeze effect.
Photo by Michael Marten
Student of group N-30
Tsvetkov E.N.
Checked:
Petrova I.F.
Moscow, 2003
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Definition.
Ebbs and flows, periodic fluctuations in water levels (rises and falls) in water areas on Earth, which are caused by the gravitational attraction of the Moon and Sun acting on the rotating Earth. All large water areas, including oceans, seas and lakes, are subject to tides to one degree or another, although in lakes they are small.
The highest water level observed in a day or half a day during high tide is called high water, the lowest level during low tide is called low water, and the moment of reaching these maximum level marks is called the standing (or stage) of high tide or low tide, respectively. Average sea level is a conditional value, above which the level marks are located during high tides, and below which during low tides. This is the result of averaging large series of urgent observations. The average height of the tide (or low tide) is an average value calculated from a large series of data on high or low water levels. Both of these middle levels are tied to the local foot rod.
Vertical fluctuations in water level during high and low tides are associated with horizontal movements of water masses in relation to the shore. These processes are complicated by wind surge, river runoff and other factors. Horizontal movements of water masses in the coastal zone are called tidal (or tidal) currents, while vertical fluctuations in water levels are called ebbs and flows. All phenomena associated with ebbs and flows are characterized by periodicity. Tidal currents periodically reverse direction, while ocean currents, moving continuously and unidirectionally, are determined by the general circulation of the atmosphere and cover large areas of the open ocean.
During transition intervals from high tide to low tide and vice versa, it is difficult to establish the trend of the tidal current. At this time (not always coinciding with the high or low tide) the water is said to “stagnate”.
High and low tides alternate cyclically in accordance with changing astronomical, hydrological and meteorological conditions. The sequence of tidal phases is determined by two maxima and two minima in the daily cycle.
Most of the volume outer space- this is emptiness. But here and there spherical clumps of matter - planets, moons, stars - rush past each other in a gigantic dance.
While performing their cosmic movements, they act on each other with the force of gravity, causing swelling of ocean waters on the surfaces of the planets. Gravity is the force of gravity that acts between all material objects without exception.
What are tides?
Ocean tides are the regular rise and fall of the water level of the World Ocean in response to gravitational influences, that is, to the forces of attraction. When the ocean waters rise to their highest level, which happens every 13 hours, it is called high tide. When the water reaches its lowest point, it is called low tide. If you come to relax on a sea beach at high tide, you observe the effect of worlds rushing past the Earth in the eternal darkness of space.
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The Sun, Moon and other bodies of the solar system influence the water and land of the Earth by the force of their gravity. But only the Moon and the Sun have a practical influence. The Sun, although very far away (149 million kilometers), is so massive that its gravitational force is strong.
The Moon is very small (its mass is 1/81 of the mass of the Earth), but it has a pronounced gravitational effect on the Earth due to its close distance from it (380,000 kilometers).
Interesting fact: When the Sun, Moon and Earth are on the same line, that is, on a new moon, the tides are especially strong.
Despite the strong gravity of the huge Sun, the small Moon, due to its proximity to the Earth, has a much greater influence on the tides. In addition, the gravitational force of the Moon varies noticeably from area to area of the earth's surface. These changes are due to the different distances of different parts of the earth's surface from the Moon at any given time.
Our planet is constantly in the gravitational field created by the Moon and the Sun. This causes a unique phenomenon expressed in the ebb and flow of tides on Earth. Let's try to figure out whether these processes affect environment and human life.
The mechanism of the phenomenon of "ebb and flow"
The nature of the formation of ebbs and flows has already been sufficiently studied. Over the years, scientists have studied the causes and results of this phenomenon.
Similar fluctuations in the level of earthly waters can be shown in the following system:
- The water level gradually rises, reaching its highest point. This phenomenon is called full water.
- After a certain period of time, the water begins to subside. Scientists gave this process the definition of “ebb.”
- For about six hours, the water continues to drain to its minimum point. This change was named in the form of the term “low water”.
You can notice a certain pattern if you observe the tide process in the same place for a month. The results of the analysis are interesting: every day low and high water changes its location. With such a natural factor as the formation of a new moon and a full moon, the levels of the objects being studied move away from each other.
Consequently, this makes the tide amplitude twice a month at its maximum. The occurrence of the smallest amplitude also occurs periodically, when, after the characteristic influence of the Moon, the levels of low and high waters gradually approach each other.
Causes of ebbs and flows on Earth
There are two factors that influence the formation of ebbs and flows. You should carefully consider both objects that affect changes in the Earth's water space.
The effect of lunar energy on the ebb and flow of tides
Although the influence of the Sun on the cause of ebb and flow is undeniable, it is still highest value in this matter belongs to the influence of lunar activity. In order to feel the significant impact of the satellite’s gravity on our planet, it is necessary to monitor the difference in the gravity of the Moon in different regions of the Earth.
The results of the experiment will show that the difference in their parameters is quite small. The thing is that the point on the earth's surface closest to the Moon is subject to external influence literally 6% more than the most distant one. It is safe to say that this disengagement of forces is pushing the Earth apart in the direction of the Moon-Earth trajectory.
Taking into account the fact that our planet constantly rotates around its axis during the day, a double tidal wave passes twice along the perimeter of the created stretch. This is accompanied by the creation of so-called double “valleys”, the height of which, in principle, does not exceed 2 meters in the World Ocean.
On the territory of the earth's land, such fluctuations reach a maximum of 40-43 centimeters, which in most cases goes unnoticed by the inhabitants of our planet.
All this leads to the fact that we do not feel the force of the ebb and flow of the tides either on land or in the water element. You can observe a similar phenomenon on a narrow strip of coastline, because the waters of the ocean or sea sometimes gain impressive heights by inertia.
From all that has been said, we can conclude that the ebb and flow of tides are most closely related to the Moon. This makes research in this area the most interesting and relevant.
The influence of solar activity on the ebb and flow of tides
The significant distance of the main star of the solar system from our planet means that its gravitational influence is less noticeable. As an energy source, the Sun is certainly much more massive than the Moon, but still makes itself felt by the impressive distance between the two celestial objects. Amplitude solar tides almost half as much as the tidal processes of the Earth's satellite.
It is a known fact that during the full moon and the waxing of the moon, all three celestial bodies a - the Earth, the Moon and the Sun - are located on the same straight line. This leads to the addition of lunar and solar tides.
During the period of direction from our planet to its satellite and main star Solar system, which differs from each other by 90 degrees, there is some influence of the Sun on the process being studied. There is an increase in the level of ebb and a decrease in the level of tide of earth's waters.
Everything indicates that solar activity also affects the energy of the tides on the surface of our planet.
Main types of tides
This concept can be classified according to the duration of the tide cycle. The demarcation will be recorded using the following points:
- Semi-diurnal changes in the water surface. Such transformations consist of two full and the same amount of incomplete water. The parameters of alternating amplitudes are almost equal to each other and look like a sinusoidal curve. They are most localized in waters Barents Sea, on the vast coastal line of the White Sea and on the territory of almost the entire Atlantic Ocean.
- Daily fluctuations in water level. Their process consists of one full and incomplete water for a period calculated within a day. A similar phenomenon has been observed in the area Pacific Ocean, and its formation is extremely rare. During the passage of the Earth's satellite through the equatorial zone, the effect of standing water is possible. If the Moon is inclined at its lowest rate, small tides of an equatorial nature occur. At the highest numbers, the process of formation of tropical tides occurs, accompanied by the greatest power of water influx.
- Mixed tides. This concept includes the presence of semidiurnal and diurnal tides of irregular configuration. Semi-diurnal changes in the level of the earth's water shell, which have an irregular configuration, are in many ways similar to semi-diurnal tides. In altered daily tides, one can observe a tendency towards daily fluctuations depending on the degree of declination of the Moon. The waters of the Pacific Ocean are most susceptible to mixed tides.
- Abnormal tides. These rises and falls of water do not fit the description of some of the signs listed above. This anomaly is associated with the concept of “shallow water,” which changes the cycle of rise and fall of water levels. The influence of this process is especially noticeable in river mouths, where high tides are shorter than low tides. A similar cataclysm can be observed in some parts of the English Channel and in the currents of the White Sea.
Earth's tide chart
There is a so-called tide table. It is necessary for people who, by the nature of their activities, depend on changes in the earth’s water level. To have accurate information on this phenomenon, you need to pay attention to:
- Designation of an area where it is important to know tide data. It is worth remembering that even closely located objects will have different characteristics of the phenomenon of interest.
- Finding the necessary information using Internet resources. For more accurate information, you can visit the port of the region being studied.
- Specification of the time of need for accurate data. This aspect depends on whether the information is needed on a specific day or the research schedule is more flexible.
- Working with the table in the mode of emerging needs. It will display all information about the tides.
- The columns at the top of the table indicate the days and dates of the alleged phenomenon. This point will make it possible to clarify the point at which the time frame of what is being studied is determined.
- Below the temporary accounting line there are numbers placed in two rows. In the format of the day, a decoding of the phases of moonrise and sunrise is placed here.
- Below is a wave-shaped chart. These indicators record the peaks (high tides) and troughs (low tides) of the waters of the study area.
- After calculating the amplitude of the waves, the data of the setting of celestial bodies are located, which affect changes in the water shell of the Earth. This aspect will allow you to observe the activity of the Moon and the Sun.
- On both sides of the table you can see numbers with plus and minus indicators. This analysis is important for determining the level of rise or fall of water, calculated in meters.
All these indicators cannot guarantee one hundred percent information, because nature itself dictates to us the parameters according to which its structural changes occur.
The influence of tides on the environment and humans
There are many factors influencing the ebb and flow of tides on human life and the environment. Among them there are discoveries of a phenomenal nature that require careful study.
Rogue waves: hypotheses and consequences of the phenomenon
This phenomenon causes a lot of controversy among people who trust only unconditional facts. The fact is that traveling waves do not fit into any system for the occurrence of this phenomenon.
The study of this object became possible with the help of radar satellites. These structures made it possible to record a dozen waves of ultra-large amplitude over a period of a couple of weeks. The size of such a rise of a body of water is about 25 meters, which indicates the enormity of the phenomenon being studied.
Rogue waves directly affect human life because last decades Such anomalies carried huge vessels such as supertankers and container ships into the ocean depths. The nature of the formation of this stunning paradox is unknown: giant waves form instantly and disappear just as quickly.
There are many hypotheses regarding the reason for the formation of such a whim of nature, but the occurrence of whirlpools (single waves due to the collision of two solitons) is possible with the intervention of the activity of the Sun and the Moon. This issue is still becoming a source of debate among scientists specializing in this topic.
The influence of tides on the organisms inhabiting the Earth
The ebb and flow of the ocean and sea especially affects marine life. This phenomenon puts the greatest pressure on residents of coastal waters. Thanks to this change in the level of earth's water, organisms leading a sedentary lifestyle develop.
These include mollusks that are perfectly adapted to vibrations liquid shell Earth. At the highest tides, oysters begin to actively reproduce, which indicates that they respond favorably to such changes in the structure of the water element.
But not all organisms react so favorably to external changes. Many species of living beings suffer from periodic fluctuations in water levels.
Although nature takes its toll and coordinates changes in the overall balance of the planet, biological substances adapt to the conditions presented to them by the activity of the Moon and the Sun.
The impact of ebbs and flows on human life
This phenomenon affects the general condition of a person more than the phases of the moon, to which the human body may be immune. However, the ebb and flow of the tides most influence the production activities of the inhabitants of our planet. It is unrealistic to influence the structure and energy of the tides of the sea, as well as the oceanic sphere, because their nature depends on the gravity of the Sun and Moon.
Basically, this cyclical phenomenon brings only destruction and trouble. Modern technologies allow this negative factor to be channeled into a positive direction.
An example of such innovative solutions would be pools designed to trap such fluctuations in water balance. They must be built taking into account that the project is cost-effective and practical.
To do this, it is necessary to create such pools of quite significant size and volume. Power plants to retain the effect of the tidal force of the Earth's water resources are new, but quite promising.
Watch a video about the ebb and flow of the tides:
The study of the concept of tides on Earth, their influence on the life cycle of the planet, the mystery of the origin of rogue waves - all these remain the main questions for scientists specializing in this field. The solution to these aspects is also interesting to ordinary people who are interested in the problems of the influence of foreign factors on planet Earth.
There is a rise and fall of water. This is the phenomenon of sea ebbs and flows. Already in ancient times, observers noticed that the tide comes some time after the culmination of the Moon at the place of observation. Moreover, the tides are strongest on new and full moon days, when the centers of the Moon and the Sun are located approximately on the same straight line.
Taking this into account, I. Newton explained the tides by the action of gravity from the Moon and the Sun, namely by the fact that different parts of the Earth are attracted by the Moon in different ways.
The Earth rotates around its axis much faster than the Moon rotates around the Earth. As a result, the tidal hump (the relative position of the Earth and the Moon is shown in Figure 38) moves, a tidal wave runs across the Earth, and tidal currents arise. As the wave approaches the shore, the height of the wave increases as the bottom rises. In inland seas, the height of a tidal wave is only a few centimeters, but in the open ocean it reaches about one meter. In favorably located narrow bays, the height of the tide increases several times more.
The friction of water against the bottom, as well as deformation of the Earth’s solid shell, are accompanied by the release of heat, which leads to the dissipation of energy from the Earth-Moon system. Since the tidal hump is to the east, the maximum tide occurs after the climax of the Moon, the attraction of the hump causes the Moon to accelerate and the Earth's rotation to slow down. The Moon is gradually moving away from the Earth. Indeed, geological data show that in the Jurassic period (190-130 million years ago) the tides were much higher and the days were shorter. It should be noted that when the distance to the Moon decreases by 2 times, the height of the tide increases 8 times. Currently, the day is increasing by 0.00017 s per year. So in about 1.5 billion years their length will increase to 40 modern days. A month will be the same length. As a result, the Earth and the Moon will always face each other with the same side. After this, the Moon will begin to gradually approach the Earth and in another 2-3 billion years it will be torn apart by tidal forces (if, of course, by that time the Solar system still exists).
Moon's influence on tide
Let us consider, following Newton, in more detail the tides caused by the attraction of the Moon, since the influence of the Sun is significantly (2.2 times) less.
Let us write down expressions for the accelerations caused by the attraction of the Moon for different points of the Earth, taking into account that for all bodies at a given point in space these accelerations are the same. In the inertial reference system associated with the center of mass of the system, the acceleration values will be:
A A = -GM / (R - r) 2 , a B = GM / (R + r) 2 , a O = -GM / R 2 ,
Where a A, a O, a B— accelerations caused by the attraction of the Moon at points A, O, B(Fig. 37); M— mass of the Moon; r— radius of the Earth; R- the distance between the centers of the Earth and the Moon (for calculations it can be taken equal to 60 r); G— gravitational constant.
But we live on Earth and carry out all observations in a reference system associated with the center of the Earth, and not with the center of mass of the Earth - Moon. To go to this system, it is necessary to subtract the acceleration of the center of the Earth from all accelerations. Then
A’ A = -GM ☾ / (R - r) 2 + GM ☾ / R 2 , a’ B = -GM ☾ / (R + r) 2 + GM / R 2 .
Let's carry out the actions in brackets and take into account that r little compared to R and in sums and differences it can be neglected. Then
A’ A = -GM / (R - r) 2 + GM ☾ / R 2 = GM ☾ (-2Rr + r 2) / R 2 (R - r) 2 = -2GM ☾ r / R 3 .
Acceleration a’A And a’B identical in magnitude, opposite in direction, each directed from the center of the Earth. They are called tidal accelerations. At points C And D tidal accelerations are smaller in magnitude and directed towards the center of the Earth.
Tidal accelerations are called accelerations that arise in a reference frame associated with a body due to the fact that, due to the finite dimensions of this body, its different parts are attracted differently by the disturbing body. At points A And B the acceleration of gravity turns out to be less than at points C And D(Fig. 37). Consequently, in order for the pressure at the same depth to be the same (as in communicating vessels) at these points, the water must rise, forming a so-called tidal hump. Calculations show that the rise of water or tide in the open ocean is about 40 cm. In coastal waters it is much greater, and the record is about 18 m. Newton's theory cannot explain this.
On the coasts of many outer seas you can see an interesting picture: fishing nets are stretched along the shore not far from the water. Moreover, these nets were not installed for drying, but for catching fish. If you stay on the shore and watch the sea, everything will become clear. Now the water begins to rise, and where just a few hours ago there was a sandbank, waves splashed. When the water receded, nets appeared, in which tangled fish sparkled with scales. The fishermen went around the nets and removed their catch. Material from the site
This is how an eyewitness describes the onset of the tide: “We reached the sea,” a fellow traveler told me. I looked around in bewilderment. In front of me there really was a shore: a trail of ripples, the half-buried carcass of a seal, rare pieces of driftwood, fragments of shells. And then there was a flat expanse... and no sea. But after about three hours, the motionless line of the horizon began to breathe and became agitated. And now the sea swell began to sparkle behind her. The tide rolled uncontrollably forward along the gray surface. Overtaking each other, the waves ran onto the shore. One after another, the distant rocks sank - and only water is visible all around. She throws salty spray in my face. Instead of a dead plain, the expanse of water lives and breathes in front of me.”
When a tidal wave enters the bay, which has a funnel-shaped plan, the shores of the bay seem to compress it, causing the height of the tide to increase several times. So, in the Bay of Fundy off the eastern shore North America the tide height reaches 18 m. In Europe, the highest tides (up to 13.5 meters) occur in Brittany near the city of Saint-Malo.
Very often a tidal wave enters the mouth
