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 the 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 high 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 caused by the general circulation of the atmosphere and cover large areas of the open ocean (see also 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.
Explanation of the origin of tidal forces. Although the Sun plays a significant role in tidal processes, the decisive factor in their development is the gravitational pull of the Moon. The degree of influence of tidal forces on each particle of water, regardless of its location on earth's surface , is determined by Newton's law of universal gravitation. 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 shift 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 approximately 89 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 displacement 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 tidal wave itself in the 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 the 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 place. 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 by: 1) the stage of development of the tide relative to the passage of the Moon; 2) the amplitude of the tide 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. Seen from the outside North Pole ecliptic, it is obvious that the Moon rotates around the Earth in the same direction in which the Earth rotates around its axis - counterclockwise. With each subsequent revolution, a given point on 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 only by the Moon's gravity. 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. IN Atlantic Ocean both spring and quadrature tides are usually delayed by a day compared to the corresponding phase of the Moon. In the Pacific Ocean, such a delay is only 5 hours. In the ports of New York and San Francisco and in the Gulf of Mexico, spring tides are 40% higher than quadrature ones.
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. This calculation is valid for the Port of New York, where the effect of the Moon at apogee or perigee is usually delayed by about 11/2 days relative to the corresponding phase of the Moon. For the port of San Francisco, the difference in tidal heights due to the Moon being at perigee or apogee is only 32%, and they follow the corresponding phases of the Moon with a delay of two days.
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 revolution 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 24 hours every half month. Thus, during the equinoxes there are periods when the declinations of both the Sun and the Moon are approximately 0°. The total tidal-generating effect of the attraction of these two bodies at such moments is most noticeably manifested 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 high tides and lower tide levels. Likewise, if the passage of aphelion coincides with apogee, lower tides and shallower tides occur.
Observation methods and forecast of tide heights. Tidal levels are measured using various types of devices. A foot rod is a regular rod with a scale in centimeters printed on it, attached vertically to a pier or to a support immersed in water so that the zero mark is below the lowest low tide level. Level changes are read directly from this scale.
Float rod. Such foot rods are used where constant waves or shallow swell make it difficult to determine the level on a fixed scale. Inside a protective well (hollow chamber or pipe) mounted vertically on seabed, a float is placed, which is connected to a pointer mounted on a fixed scale, or to a recorder pen. Water enters the well through a small hole located well below the minimum sea level. Its tidal changes are transmitted through the float to measuring instruments.
Hydrostatic sea level recorder. A block of rubber bags is placed at a certain depth. As the height of the tide (layer of water) changes, the hydrostatic pressure changes, which is recorded by measuring instruments. Automatic recording devices (tide gauges) can also be used to obtain a continuous record of tidal fluctuations at any point.
Tide tables. There are two main methods used in compiling tide tables: harmonic and non-harmonic. The non-harmonic method is entirely based on observational results. In addition, the characteristics of port waters and some basic astronomical data are involved (the hour angle of the Moon, the time of its passage through the celestial meridian, phases, declination and parallax). After making adjustments for the listed factors, calculating the moment of onset and level of tide for any port is a purely mathematical procedure. The harmonic method is partly analytical and partly based on observations of tide heights carried out over at least one lunar month. To confirm this type of forecast for each port, long series of observations are required, since distortions arise due to physical phenomena such as inertia and friction, as well as the complex configuration of the shores of the water area and the features of the bottom topography. Since tidal processes are characterized by periodicity, harmonic vibration analysis is applied to them. The observed tide is considered to be the result of the addition of a series of simple component tidal waves, each of which is caused by one of the tidal forces or one of the factors. For a complete solution, 37 such simple components are used, although in some cases additional components beyond the basic 20 are negligible. Simultaneous substitution of 37 constants into the equation and its actual solution is carried out on a computer.
River tides and currents. The interaction of tides and river currents is clearly visible where large rivers flow into the ocean. Tidal heights in bays, estuaries and estuaries can increase significantly as a result of increased flows in marginal streams, especially during floods. At the same time, ocean tides penetrate far up rivers in the form of tidal currents. For example, on the Hudson River a tidal wave reaches a distance of 210 km from the mouth. Tidal currents usually travel upriver to intractable waterfalls or rapids. During high tides, river currents are faster than during low tides. Maximum speeds tidal currents reach 22 km/h.
Bor. When water moves under the influence of the tide high altitude, limited in its movement by a narrow channel, a rather steep wave is formed, which moves upstream as a single front. This phenomenon is called a tidal wave, or bore. Such waves are observed on rivers much higher than their mouths, where the combination of friction and river current most impedes the spread of the tide. The phenomenon of boron formation in the Bay of Fundy in Canada is known. Near Moncton (New Brunswick), the Pticodiac River flows into the Bay of Fundy, forming a marginal stream. At low water its width is 150 m, and it crosses the drying strip. At high tide, a wall of water 750 m long and 60-90 cm high rushes up the river in a hissing and seething vortex. The largest known pine forest, 4.5 m high, is formed on the Fuchunjiang River, which flows into Hanzhou Bay. See also BOR. A reversing waterfall (reversing direction) is another phenomenon associated with tides in rivers. A typical example is the waterfall on the Saint John River (New Brunswick, Canada). Here, through a narrow gorge, water during high tide penetrates into the basin located above the level low water, however, slightly below the full water level in the same gorge. Thus, a barrier arises, flowing through which water forms a waterfall. During low tide, the water flows downstream through a narrowed passage and, overcoming an underwater ledge, forms an ordinary waterfall. During high tide, a steep wave that penetrates the gorge falls like a waterfall into the overlying basin. The backward flow continues until the water levels on both sides of the threshold are equal and the tide begins to ebb. Then the waterfall facing downstream is restored again. The average water level difference in the gorge is approx. 2.7 m, however, at the highest tides, the height of the direct waterfall can exceed 4.8 m, and the reverse one - 3.7 m.
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.
Wind and weather. The wind is exerting significant influence to tidal phenomena. 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. Due to the increase 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 mmHg. Art., the water level drops by approximately 33 cm. The decrease in atmospheric pressure causes a corresponding increase in the water level. 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. The formation of these waves can be associated either with hurricane force winds or with underwater earthquakes (in the latter case they are called seismic sea waves, or tsunamis).
Using tidal energy. Four methods have been developed to harness tidal energy, but the most practical is to create a tidal pool system. At the same time, fluctuations in water levels associated with tidal phenomena are used in the lock system so that a level difference is constantly maintained, which allows energy to be generated. The power of tidal power plants directly depends on the area of ​​the trap pools and the potential level difference. The latter factor, in turn, is a function of the amplitude of tidal fluctuations. The achievable level difference is by far the most important for power generation, although the cost of the structures depends on the area of ​​the basins. Currently, large tidal power plants operate in Russia on the Kola Peninsula and in Primorye, in France in the Rance River estuary, in China near Shanghai, as well as in other areas of the globe.
LITERATURE
Shuleykin V.V. Physics of the sea. M., 1968 Harvey J. Atmosphere and ocean. M., 1982 Drake Ch., Imbrie J., Knaus J., Turekian K. The ocean by itself and for us. M., 1982

Collier's Encyclopedia. - Open Society. 2000 .

Seas and oceans move away from the shore twice a day (low tide) and approach it twice a day (high tide). On some bodies of water there are practically no tides, while on others the difference between low and high tide along the coastline can be up to 16 meters. Most tides are semidiurnal (twice a day), but in some places they are diurnal, that is, the water level changes only once a day (one low tide and one high tide).

The ebb and flow of the tides is most noticeable in the coastal stripes, but in fact they pass throughout 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, so its influence on the planets is stronger even though the natural satellite is much smaller, and both celestial bodies revolve around the star.

Moon's influence on tides

If continents and islands did not interfere with the influence of the Moon on water, and the entire surface of the Earth was covered by an ocean of equal depth, then the tides would look like this. Due to the force of gravity, the section of the ocean closest to the Moon would rise towards the natural satellite; due to centrifugal force, the opposite part of the reservoir would also rise, this would be a tide. The drop in 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 influence on the world's oceans. During the new moon and full moon, when the Moon and the Sun are located in a straight line with the Earth, the attractive force of both luminaries is added, thereby causing the strongest ebbs and flows. If these celestial bodies are perpendicular to each other in relation to the Earth, then the two forces of gravity will counteract each other, and the tides will be weakest, but still in favor of the Moon.

The presence of different islands brings great variety to the movement of water during ebb and flow. On some reservoirs, the channel and natural obstacles in the form of land (islands) play an important role, so the 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.

Let's continue the conversation about the forces acting on celestial bodies and the effects caused by this. Today I will talk about tides and non-gravitational disturbances.

What does this mean – “non-gravitational disturbances”? Perturbations are usually called small corrections to a large, main force. That is, we will talk about some forces, the influence of which on an object is much less than gravitational ones

What other forces exist in nature besides gravity? Let us leave aside strong and weak nuclear interactions; they are local in nature (act at extremely short distances). But electromagnetism, as we know, is much stronger than gravity and extends just as far - infinitely. But since electric charges of opposite signs are usually balanced, and the gravitational “charge” (the role of which is played by mass) is always of the same sign, then with sufficiently large masses, of course, gravity comes to the fore. So in reality we will be talking about disturbances in the movement of celestial bodies under the influence of an electromagnetic field. There are no more options, although there is still dark energy, but we will talk about it later, when we talk about cosmology.

As I explained on , Newton's simple law of gravity F = G∙M∙m/R² is very convenient to use in astronomy, because most bodies have a close to spherical shape and are sufficiently distant from each other, so that when calculating they can be replaced by points - point objects containing their entire mass. But a body of finite size, comparable to the distance between neighboring bodies, nevertheless experiences different force influences in its different parts, because these parts are located differently from the sources of gravity, and this must be taken into account.

Attraction crushes and tears apart

To feel the tidal effect, let's do a thought experiment popular among physicists: imagine ourselves in a freely falling elevator. We cut off the rope holding the cabin and begin to fall. Before we fall, we can watch what is happening around us. We hang free masses and observe how they behave. At first they fall synchronously, and we say this is weightlessness, because all the objects in this cabin and it itself feel approximately the same acceleration of free fall.

But over time, our material points will begin to change their configuration. Why? Because the lower one at the beginning was a little closer to the center of attraction than the upper one, so the lower one, being attracted stronger, begins to outstrip the upper one. And the side points always remain at the same distance from the center of gravity, but as they approach it they begin to approach each other, because accelerations of equal magnitude are not parallel. As a result, the system of unconnected objects is deformed. This is called the tidal effect.

From the point of view of an observer who has scattered grain around himself and watches how individual grains move while the whole system falls on massive object, we can introduce such a concept as a tidal force field. Let us define these forces at each point as the vector difference between the gravitational acceleration at this point and the acceleration of the observer or the center of mass, and if we take only the first term of the expansion in the Taylor series for relative distance, we will get a symmetrical picture: the nearest grains will be ahead of the observer, the distant ones will lag behind him, i.e. the system will stretch along the axis directed towards the gravitating object, and along directions perpendicular to it the particles will be pressed towards the observer.

What do you think will happen when a planet is pulled into a black hole? Those who have not listened to lectures on astronomy usually think that black hole Only from the surface facing itself will the substance be torn off. They do not know that an almost equally strong effect occurs on back side freely falling body. Those. it is torn in two diametrically opposite directions, not in one at all.

The Dangers of Outer Space

To show how important it is to take into account the tidal effect, take the International space station. It, like all Earth satellites, falls freely in a gravitational field (if the engines are not turned on). And the field of tidal forces around it is a quite tangible thing, so the astronaut, when working on the outside of the station, must tie himself to it, and, as a rule, with two cables - just in case, you never know what might happen. And if he finds himself untethered in those conditions where tidal forces pull him away from the center of the station, he can easily lose contact with it. This often happens with tools, because you can’t link them all. If something falls out of an astronaut’s hands, then this object goes into the distance and becomes an independent satellite of the Earth.

The work plan for the ISS includes tests in outer space of a personal jetpack. And when his engine fails, tidal forces carry the astronaut away, and we lose him. The names of the missing are classified.

This is, of course, a joke: fortunately, such an incident has not happened yet. But this could very well happen! And maybe someday it will happen.

Planet-ocean

Let's return to Earth. This is the most interesting object for us, and the tidal forces acting on it are felt quite noticeably. From which celestial bodies do they act? The main one is the Moon, because it is close. The next largest impact is the Sun, because it is massive. The other planets also have some influence on the Earth, but it is barely noticeable.

To analyze external gravitational influences on the Earth, it is usually represented as a solid ball covered with a liquid shell. This is a good model, since our planet actually has a mobile shell in the form of ocean and atmosphere, and everything else is quite solid. Although the Earth's crust and inner layers have limited rigidity and are slightly susceptible to tidal influence, their elastic deformation can be neglected when calculating the effect on the ocean.

If we draw tidal force vectors in the Earth’s center of mass system, we get the following picture: the field of tidal forces pulls the ocean along the Earth-Moon axis, and in a plane perpendicular to it presses it to the center of the Earth. Thus, the planet (at least its moving shell) tends to take the shape of an ellipsoid. In this case, two bulges appear (they are called tidal humps) on opposite sides of the globe: one faces the Moon, the other faces away from the Moon, and in the strip between them, a corresponding “bulge” appears (more precisely, the surface of the ocean there has less curvature).

A more interesting thing happens in the gap - where the tidal force vector tries to move the liquid shell along the earth's surface. And this is natural: if you want to raise the sea in one place, and lower it in another place, then you need to move the water from there to here. And between them, tidal forces drive water to the “sublunar point” and to the “anti-lunar point.”

Quantifying the tidal effect is very simple. The Earth's gravity tries to make the ocean spherical, and the tidal part of the lunar and solar influence– pull it along the axis. If we left the Earth alone and allowed it to fall freely onto the Moon, the height of the bulge would reach about half a meter, i.e. The ocean rises only 50 cm above its average level. If you are traveling by boat on open sea or the ocean, half a meter is not noticeable. This is called static tide.

But in order to create a half-meter bulge at the sublunar point, you need to distill a large amount of water here. But the surface of the Earth does not remain motionless, it rotates quickly in relation to the direction of the Moon and the Sun, making a full revolution in a day (and the Moon moves slowly in orbit - one revolution around the Earth in almost a month). Therefore, the tidal hump constantly runs along the surface of the ocean, so that the solid surface of the Earth is under the tidal hump 2 times per day and 2 times under the tidal drop in ocean level. Let's estimate: 40 thousand kilometers (the length of the earth's equator) per day, that's 463 meters per second. This means that this half-meter wave, like a mini-tsunami, hits the eastern coasts of the continents in the equator region at supersonic speed. At our latitudes, the speed reaches 250-300 m/s - also quite a lot: although the wave is not very high, due to inertia it can create a great effect.

The second object in terms of influence on the Earth is the Sun. It is 400 times farther from us than the Moon, but 27 million times more massive. Therefore, the effects from the Moon and from the Sun are comparable in magnitude, although the Moon still acts a little stronger: the gravitational tidal effect from the Sun is about half as weak as from the Moon. Sometimes their influence is combined: this happens on a new moon, when the Moon passes against the background of the Sun, and on a full moon, when the Moon is on the opposite side from the Sun. On these days - when the Earth, Moon and Sun line up, and this happens every two weeks - the total tidal effect is one and a half times greater than from the Moon alone. And after a week, the Moon passes a quarter of its orbit and finds itself in quadrature with the Sun (a right angle between the directions on them), and then their influence weakens each other. On average, the height of tides in the open sea varies from a quarter of a meter to 75 centimeters.

Sailors have known tides for a long time. What does the captain do when the ship runs aground? If you have read sea adventure novels, then you know that he immediately looks at what phase the Moon is in and waits for the next full moon or new moon. Then the maximum tide can lift the ship and refloat it.

Coastal problems and features

Tides are especially important for port workers and for sailors who are about to bring their ship into or out of port. As a rule, the problem of shallow water arises near the coast, and to prevent it from interfering with the movement of ships, underwater channels - artificial fairways - are dug to enter the bay. Their depth should take into account the height of the maximum low tide.

If we look at the height of the tides at some point in time and draw lines of equal heights of water on the map, we will get concentric circles with centers at two points (sublunar and anti-lunar), in which the tide is maximum. If the orbital plane of the Moon coincided with the plane of the Earth’s equator, then these points would always move along the equator and would make a full revolution per day (more precisely, in 24ʰ 50ᵐ 28ˢ). However, the Moon does not move in this plane, but near the ecliptic plane, in relation to which the equator is inclined by 23.5 degrees. Therefore, the sublunar point also “walks” along latitude. Thus, in the same port (i.e., at the same latitude), the height of the maximum tide, which repeats every 12.5 hours, changes during the day depending on the orientation of the Moon relative to the Earth's equator.

This “trifle” is important for the theory of tides. Let's look again: the Earth rotates around its axis, and the plane of the lunar orbit is inclined towards it. Therefore, each seaport “runs” around the Earth’s pole during the day, once falling into the region of the highest tide, and after 12.5 hours - again into the region of the tide, but less high. Those. two tides during the day are not equal in height. One is always larger than the other, because the plane of the lunar orbit does not lie in the plane of the earth's equator.

For coastal residents, the tidal effect is vital. For example, in France there is one that is connected to the mainland by an asphalt road laid along the bottom of the strait. There are many people living on the island, but they cannot use this road while the sea level is high. This road can only be driven twice a day. People drive up and wait for low tide, when the water level drops and the road becomes accessible. People travel to and from work on the coast using a special tide table that is published for each coastal settlement. If this phenomenon is not taken into account, water may overwhelm a pedestrian along the way. Tourists simply come there and walk around to look at the bottom of the sea when there is no water. And local residents collect something from the bottom, sometimes even for food, i.e. in essence, this effect feeds people.

Life came out of the ocean thanks to the ebb and flow of the tides. As a result of the low tide, some coastal animals found themselves on the sand and were forced to learn to breathe oxygen directly from the atmosphere. If there were no Moon, then life might not have come out of the ocean so actively, because it is good there in all respects - a thermostatic environment, weightlessness. But if you suddenly found yourself on the shore, you had to somehow survive.

The coast, especially if it is flat, is greatly exposed at low tide. And for some time people lose the opportunity to use their watercraft, lying helplessly like whales on the shore. But there is something useful in this, because the low tide period can be used to repair ships, especially in some bay: the ships sailed, then the water went away, and they can be repaired at this time.

For example, there is the Bay of Fundy on the east coast of Canada, which is said to have the highest tides in the world: the water level drop can reach 16 meters, which is considered a record for a sea tide on Earth. Sailors have adapted to this property: during high tide they bring the ship to the shore, strengthen it, and when the water goes away, the ship hangs, and the bottom can be caulked.

People have long begun to monitor and regularly record the moments and characteristics of high tides in order to learn how to predict this phenomenon. Soon invented tide gauge- a device in which a float moves up and down depending on sea level, and the readings are automatically drawn on paper in the form of a graph. By the way, the means of measurement have hardly changed since the first observations to the present day.

Based on a large number of hydrograph records, mathematicians are trying to create a theory of tides. If you have a long-term record of a periodic process, you can decompose it into elementary harmonics - sinusoids of different amplitudes with multiple periods. And then, having determined the parameters of the harmonics, extend the total curve into the future and make tide tables on this basis. Nowadays such tables are published for every port on Earth, and any captain about to enter a port takes a table for him and sees when there will be sufficient water level for his ship.

The most famous story related to predictive calculations occurred during the Second World War. world war: in 1944, our allies - the British and Americans - were going to open a second front against Hitler's Germany, for this it was necessary to land on the French coast. The northern coast of France is very unpleasant in this regard: the coast is steep, 25-30 meters high, and the ocean bottom is quite shallow, so ships can only approach the coast at times of maximum tide. If they ran aground, they would simply be shot from cannons. To avoid this, a special mechanical (there were no electronic ones yet) computer was created. She performed Fourier analysis of sea-level time series using drums rotating at their own speed, through which a metal cable passed, which summed up all the terms of the Fourier series, and a feather connected to the cable plotted a graph of tide height versus time. This was top secret work that greatly advanced the theory of tides because it was possible to predict with sufficient accuracy the moment of the highest tide, thanks to which heavy military transport ships swam across the English Channel and landed troops ashore. This is how mathematicians and geophysicists saved the lives of many people.

Some mathematicians are trying to generalize the data on a planetary scale, trying to create a unified theory of tides, but comparing records made in different places is difficult because the Earth is so irregular. It is only in the zero approximation that a single ocean covers the entire surface of the planet, but in reality there are continents and several weakly connected oceans, and each ocean has its own frequency of natural oscillations.

Previous discussions about sea level fluctuations under the influence of the Moon and the Sun concerned open ocean spaces, where tidal acceleration varies greatly from one coast to another. And in local bodies of water - for example, lakes - can the tide create a noticeable effect?

It would seem that it should not be, because at all points of the lake the tidal acceleration is approximately the same, the difference is small. For example, in the center of Europe there is Lake Geneva, it is only about 70 km long and is in no way connected with the oceans, but people have long noticed that there are significant daily fluctuations in water there. Why do they arise?

Yes, the tidal force is extremely small. But the main thing is that it is regular, i.e. operates periodically. All physicists know the effect that, when a force is applied periodically, sometimes causes an increased amplitude of oscillations. For example, you take a bowl of soup from the cafeteria and... This means that the frequency of your steps is in resonance with the natural vibrations of the liquid in the plate. Noticing this, we sharply change the pace of walking - and the soup “calms down.” Each body of water has its own basic resonant frequency. And what larger size reservoir, the lower the frequency of natural vibrations of the liquid in it. So, Lake Geneva’s own resonant frequency turned out to be a multiple of the frequency of the tides, and a small tidal influence “looses” Lake Geneva so that the level on its shores changes quite noticeably. These long-period standing waves that occur in closed bodies of water are called seiches.

Tidal Energy

Nowadays, they are trying to connect one of the alternative energy sources with the tidal effect. As I said, the main effect of tides is not that the water rises and falls. The main effect is a tidal current that moves water around the entire planet in a day.

In shallow places this effect is very important. In the New Zealand area, captains do not even risk guiding ships through some straits. Sailboats have never been able to get through there, and even modern ships have difficulty getting through there, because the bottom is shallow and tidal currents have enormous speed.

But since the water is flowing, this kinetic energy can be used. And power plants have already been built, in which turbines rotate back and forth due to tidal currents. They are quite functional. The first tidal power plant (TPP) was made in France, it is still the largest in the world, with a capacity of 240 MW. Compared to a hydroelectric power station, it’s not so great, of course, but it serves the nearest rural areas.

The closer to the pole, the lower the speed of the tidal wave, therefore in Russia there are no coasts that would have very powerful tides. In general, we have few outlets to the sea, and the coast of the Arctic Ocean is not particularly profitable for using tidal energy, also because the tide drives water from east to west. But there are still places suitable for PES, for example, Kislaya Bay.

The fact is that in bays the tide always creates a greater effect: the wave runs up, rushes into the bay, and it narrows, narrows - and the amplitude increases. A similar process occurs as if a whip was cracked: at first the long wave travels slowly along the whip, but then the mass of the part of the whip involved in the movement decreases, so the speed increases (impulse mv is preserved!) and reaches supersonic at the narrow end, as a result of which we hear a click.

By creating the experimental Kislogubskaya TPP of low power, power engineers tried to understand how effectively tides at circumpolar latitudes can be used to produce electricity. It doesn't make much economic sense. However, now there is a project for a very powerful Russian TPP (Mezenskaya) - for 8 gigawatts. In order to achieve this colossal power, it is necessary to block off a large bay, separating the White Sea from the Barents Sea with a dam. True, it is highly doubtful that this will be done as long as we have oil and gas.

The past and future of tides

By the way, where does tidal energy come from? The turbine spins, electricity is generated, and what object loses energy?

Since the source of tidal energy is the rotation of the Earth, if we draw from it, it means that the rotation must slow down. It would seem that the Earth has internal sources of energy (heat from the depths comes from geochemical processes and the decay of radioactive elements), and there is something to compensate for the loss of kinetic energy. This is true, but the energy flow, spreading on average almost evenly in all directions, can hardly significantly affect the angular momentum and change the rotation.

If the Earth did not rotate, the tidal humps would point exactly in the direction of the Moon and the opposite direction. But, as it rotates, the Earth’s body carries them forward in the direction of its rotation - and a constant divergence of the tidal peak and the sublunar point of 3-4 degrees arises. What does this lead to? The hump that is closer to the Moon is attracted to it more strongly. This gravitational force tends to slow down the Earth's rotation. And the opposite hump is further from the Moon, it tries to speed up the rotation, but is attracted weaker, so the resultant moment of force has a braking effect on the rotation of the Earth.

So, our planet is constantly decreasing its rotation speed (though not quite regularly, in jumps, which is due to the peculiarities of mass transfer in the oceans and atmosphere). What effect do Earth's tides have on the Moon? The near tidal bulge pulls the Moon along with it, while the distant one, on the contrary, slows it down. The first force is greater, as a result the Moon accelerates. Now remember from the previous lecture, what happens to a satellite that is forcibly pulled forward in motion? As its energy increases, it moves away from the planet and its angular velocity decreases because the orbital radius increases. By the way, an increase in the period of revolution of the Moon around the Earth was noticed back in the time of Newton.

Speaking in numbers, the Moon moves away from us by about 3.5 cm per year, and the length of the Earth’s day increases by a hundredth of a second every hundred years. It seems like nonsense, but remember that the Earth has existed for billions of years. It is easy to calculate that in the time of dinosaurs there were about 18 hours in a day (the current hours, of course).

As the Moon moves away, tidal forces become smaller. But it was always moving away, and if we look into the past, we will see that before the Moon was closer to the Earth, which means the tides were higher. You can appreciate, for example, that in the Archean era, 3 billion years ago, the tides were kilometer high.

Tidal phenomena on other planets

Of course, the same phenomena occur in the systems of other planets with satellites. Jupiter, for example, is a very massive planet with big number satellites. Its four largest satellites (they are called Galilean because Galileo discovered them) are quite significantly influenced by Jupiter. The nearest of them, Io, is entirely covered with volcanoes, among which there are more than fifty active ones, and they emit “extra” matter 250-300 km upward. This discovery was quite unexpected: there are no such powerful volcanoes on Earth, but here small body the size of the Moon, which should have cooled down long ago, but instead it radiates heat in all directions. Where is the source of this energy?

Io's volcanic activity was not a surprise to everyone: six months before the first probe approached Jupiter, two American geophysicists published a paper in which they calculated Jupiter's tidal influence on this moon. It turned out to be so large that it could deform the satellite’s body. And during deformation, heat is always released. When we take a piece of cold plasticine and begin to knead it in our hands, after several compressions it becomes soft and pliable. This happens not because the hand heated it with its heat (the same thing will happen if you squish it in a cold vice), but because the deformation put mechanical energy into it, which was converted into thermal energy.

But why on earth does the shape of the satellite change under the influence of tides from Jupiter? It would seem that, moving in a circular orbit and rotating synchronously, like our Moon, it once became an ellipsoid - and there is no reason for subsequent distortions of the shape? However, there are also other satellites near Io; all of them cause its (Io) orbit to shift slightly back and forth: it either approaches Jupiter or moves away. This means that the tidal influence either weakens or intensifies, and the shape of the body changes all the time. By the way, I have not yet talked about tides in the solid body of the Earth: of course, they also exist, they are not so high, on the order of a decimeter. If you sit in your place for six hours, then, thanks to the tides, you will “walk” about twenty centimeters relative to the center of the Earth. This vibration is imperceptible to humans, of course, but geophysical instruments register it.

Unlike the solid earth, the surface of Io fluctuates with an amplitude of many kilometers during each orbital period. A large amount of deformation energy is dissipated as heat and heats the subsurface. By the way, meteorite craters are not visible on it, because volcanoes constantly bombard the entire surface with fresh matter. As soon as an impact crater is formed, a hundred years later it is covered with products of eruptions of neighboring volcanoes. They work continuously and very powerfully, and to this are added fractures in the planet’s crust, through which a melt of various minerals, mainly sulfur, flows from the depths. At high temperature it darkens, so the stream from the crater looks black. And the light rim of the volcano is the cooled substance that falls around the volcano. On our planet, matter ejected from a volcano is usually decelerated by air and falls close to the vent, forming a cone, but on Io there is no atmosphere, and it flies along a ballistic trajectory far in all directions. Perhaps this is an example of the most powerful tidal effect in the solar system.

The second satellite of Jupiter, Europa, all looks like our Antarctica, it is covered with a continuous ice crust, cracked in some places, because something is constantly deforming it too. Since this satellite is further away from Jupiter, the tidal effect here is not so strong, but still quite noticeable. Beneath this icy crust is a liquid ocean: the photographs show fountains gushing out of some of the cracks that have opened up. Under the influence of tidal forces, the ocean rages, and ice fields float and collide on its surface, much like we have in the Arctic Ocean and off the coast of Antarctica. The measured electrical conductivity of Europa's ocean fluid suggests that it salty water. Why shouldn't there be life there? It would be tempting to lower a device into one of the cracks and see who lives there.

In fact, not all planets meet ends meet. For example, Enceladus, a moon of Saturn, also has an icy crust and an ocean underneath. But calculations show that tidal energy is not enough to maintain the subglacial ocean in a liquid state. Of course, in addition to tides, any celestial body has other sources of energy - for example, decaying radioactive elements (uranium, thorium, potassium), but on small planets they can hardly play a significant role. This means there is something we don’t understand yet.

The tidal effect is extremely important for stars. Why - more on this in the next lecture.

MOSCOW STATE UNIVERSITY OF ENVIRONMENTAL ENGINEERING

Abstract on "Earth Sciences"

Subject: "Ebbs and flows"

Completed:

Student of group N-30

Tsvetkov E.N.

Checked:

Petrova I.F.

Moscow, 2003

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 the 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 high 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 (which does not always coincide 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.

The essence of the phenomenon.

Although the Sun plays a significant role in tidal processes, the decisive factor in their development is the gravitational pull of the Moon. The degree of influence of tidal forces on each particle of water, regardless of its location on the earth's surface, is determined by Newton's law of universal gravitation. 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 displacement 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 tidal wave itself in the 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 the 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 place. 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 by: 1) the stage of development of the tide relative to the passage of the Moon; 2) the amplitude of the tide 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. With each subsequent revolution, a given point on 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 14 3/4 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 only by the Moon's gravity. 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. In the Atlantic Ocean, both spring and quadrature tides are usually delayed by a day compared to the corresponding phase of the Moon. In the Pacific Ocean, such a delay is only 5 hours. In the ports of New York and San Francisco and in the Gulf of Mexico, spring tides are 40% higher than quadrature ones.

Lunar The period of fluctuations in tidal heights, which occurs due to lunar parallax, is 27 1/2 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. This calculation is valid for the Port of New York, where the effect of the Moon at apogee or perigee is usually delayed by about 1 1/2 days relative to the corresponding phase of the Moon. For the port of San Francisco, the difference in tidal heights due to the Moon being at perigee or apogee is only 32%, and they follow the corresponding phases of the Moon with a delay of two days.

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 revolution 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 24 hours 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-generating effect of the attraction of these two bodies at such moments is most noticeably manifested 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.

Sunny parallactic 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 net tidal force, higher tidal levels and lower tidal levels can be expected. Likewise, if the passage of aphelion coincides with apogee, lower tides and shallower tides occur.

Change over time.

The phenomenon of ebb and flow of tides has not changed over time, since the movement of both the Moon and the Sun remains the same as a thousand years ago - namely, the movement of these two celestial bodies influences the ebb and flow of the tides on Earth.

Distribution and scale of manifestation.

The magnitude and nature of tides in various parts of the coast of the World Ocean depend on the configuration of the coasts, the angle of inclination of the seabed and a number of other reasons. They most typically appear on the open ocean coast. The penetration of tidal waves into inland seas is difficult, and therefore the amplitude of the tides in them is small.

The narrow, shallow Danish Straits reliably shield the Baltic Sea from the tides. Theoretical calculations show that the amplitude of fluctuations in the height of the water level in the Baltic is approximately 10 centimeters, but it is almost impossible to see these tides, since they are completely erased by fluctuations in the water level under the influence of wind or changes in atmospheric pressure. Our southern seas - the Black and Azov seas, which communicate with the waters of the World Ocean through a number of narrow straits, and the internal Aegean and Mediterranean seas - are even more reliably protected from tidal waves. If the difference in water level during high and low tide on the Atlantic coast of Spain near Gibraltar reached 3 meters, then in the Mediterranean Sea near the strait it is only 1.3 meters. In other parts of the sea, the tides are even less significant and usually do not exceed 0.5 meters. In the Aegean Sea and the Bosphorus and Dardanelles straits, the tidal wave attenuates even more. Therefore, in the Black Sea, fluctuations in water level under the influence of tides are less than 10 centimeters. In the Sea of ​​Azov, connected to the Black Sea only by the narrow Kerch Strait, the tidal amplitude is close to zero.

For the same reason, the tides in the Sea of ​​Japan are very low - here they barely reach 0.5 meters.

If in inland seas the magnitude of tides is reduced compared to the open ocean coast, then in bays and bays that have a wide connection with the ocean, it increases. The tidal wave enters such bays freely. The water masses rush forward, but, constrained by the narrowing banks and not finding a way out, they rise up and flood the land to a considerable height.

At the entrance to the White Sea, in the so-called Voronka, the tides are almost the same as on the coast of the Barents Sea, that is, equal to 4–5 meters. At Cape Kanin Nos they do not even exceed 3 meters. However, entering the gradually narrowing Funnel of the White Sea, the tidal wave becomes higher and higher and in the Mezen Bay reaches a height of ten meters.

The rise in water level in the northernmost part of the Sea of ​​Okhotsk is even more significant. Thus, at the entrance to Shelikhov Bay, the sea level at high tide rises to 4–5 meters, in the apex (furthest from the sea) part of the bay it rises to 9.5 meters, and in Penzhinskaya Bay it reaches almost 13 meters!

Tides in the English Channel are very high. On the English coast, in the small Bay of Lyme, the water in syzygy rises to 14.4 meters, and on the French, near the town of Granville, even 15 meters.

Tides reach extreme values ​​in some areas of the Atlantic coast of Canada. In Frobisher Strait (located at the entrance to Hudson Strait) - 15.6 meters, and in the Bay of Fundy (near the US border) - as much as 18 meters.

Sometimes the influence of sea tides is visible on rivers. In the estuary region, a tidal wave comes from open areas of the ocean or sea. As you approach the shore, the level rises, and the profile of the tidal wave, under the influence of a decrease in depth and features of the shore configuration, is deformed. At the seaside, its front slope becomes steeper than its back slope. From the mouth coastal area, the tidal wave penetrates into the river channel system. The saltier water along the bottom of the river bed, like a wedge, rapidly moves against the current. The collision of two oncoming flows, sea and river, causes the formation of a steep shaft, called bora. In the Cantanjiang River, which flows into the East China Sea south of Shanghai, the bore reaches a height of 7 - 8 meters, and the steepness of the wave is 70 degrees. This terrible wall of water rushes up the river at a speed of 15 - 16 kilometers per hour, eroding the banks and threatening to sink any ship that does not take refuge in the calm backwater in time. It is also famous for its powerful boron greatest river South America - Amazon. There, a wave 5-6 meters high travels up the river three thousand kilometers from the ocean. On the Mekong, tidal waves extend up to 500 km, on the Mississippi - up to 400 km, on the Northern Dvina - up to 140 km. The tide carries salty waters into the river. In this case, at the mouth of the river, either complete or partial mixing of river and salty sea waters occurs, or a stratified state occurs, when a sharp difference in the salinity of the surface and underlying waters is observed. Salt water penetrates into the mouth of the river the further the more depth channels and density (salinity) sea ​​water and less river water consumption.

Myths and legends.

For a long time, the causes of tides remained unclear. In ancient times, they were explained by the breath of the Ocean deity living in the sea, or as a consequence of the breathing of the planet. Other fantastic assumptions have been made about the nature of the tides. (also see section History of the study)

The ebb and flow of the tides is currently believed to be caused by the gravitational pull of the Moon. So, the Earth turns to the satellite in one direction or another, the Moon attracts this water to itself - these are the tides. In the area where the water leaves there are low tides. The earth rotates, ebbs and flows change each other. This is the lunar theory, in which everything is good except for a number of unexplained facts.

For example, did you know that the Mediterranean Sea is considered tidal, but near Venice and on the Eurekos Strait in eastern Greece, the tides are up to one meter or more. This is considered one of the mysteries of nature. However, Italian physicists discovered in the eastern Mediterranean Sea, at a depth of more than three kilometers, a chain of underwater whirlpools, each ten kilometers in diameter. Interesting coincidence of abnormal tides and whirlpools, isn't it?

A pattern has been noticed: where there are whirlpools, in oceans, seas and lakes, there are ebbs and flows, and where there are no whirlpools, there are no ebbs and flows... The vastness of the world's oceans is completely covered with whirlpools, and whirlpools have the property of a gyroscope to maintain the position of the axis in space, regardless of the rotation of the earth.

If you look at the earth from the side of the Sun, the whirlpools, rotating with the Earth, overturn twice a day, as a result of which the axis of the whirlpools precesses (1-2 degrees) and creates a tidal wave, which is the cause of ebbs and flows, and the vertical movement of ocean waters .

Precession of a top

Giant ocean whirlpool

The Mediterranean Sea is considered tidal, but near Venice and on the Eurekos Strait in eastern Greece, the tides are up to one meter or more. And this is considered one of the mysteries of nature, but at the same time, Italian physicists discovered in the east of the Mediterranean Sea, at a depth of more than three kilometers, a chain of underwater whirlpools, each ten kilometers in diameter. From this we can conclude that along the coast of Venice, at a depth of several kilometers, there is a chain of underwater whirlpools.

If in the Black Sea the water rotated like in the White Sea, then the ebb and flow of the tides would be more significant. If a bay is flooded by a tidal wave and the wave swirls there, then the ebbs and flows in this case are higher... The place of whirlpools, and atmospheric cyclones and anticyclones in science, at the intersection of oceanology, meteorology, and celestial mechanics studying gyroscopes. The behavior of atmospheric cyclones and anticyclones, I believe, is similar to the behavior of whirlpools in the oceans.

To test this idea, I mounted a fan on the globe, where the whirlpool is located, and instead of blades I inserted metal balls on springs. I turned on the fan (whirlpool), simultaneously rotating the globe both around its axis and around the Sun, and got an imitation of the ebb and flow of the tides.

The attractiveness of this hypothesis is that it can be quite convincingly tested using a whirlpool fan attached to the globe. The sensitivity of the whirlpool gyroscope is so high that the globe has to be rotated extremely slowly (one revolution every 5 minutes). And if a whirlpool gyroscope is installed on a globe at the mouth of the Amazon River, then without a doubt, it will show the exact mechanics of the ebb and flow of the Amazon River. When only the globe rotates around its axis, the gyroscope-whirlpool tilts in one direction and stands motionless, and if the globe is moved in orbit, the whirlpool-horoscope begins to oscillate (precess) and gives two ebbs and flows per day.

Doubts about the presence of precession in whirlpools, as a result of slow rotation, are removed by the high speed of overturning of whirlpools, in 12 hours.. And we must not forget that the orbital speed of the earth is thirty times greater than the orbital speed of the moon.

The experience with the globe is more convincing than the theoretical description of the hypothesis. The drift of whirlpools is also associated with the effect of a gyroscope - a whirlpool, and depending on which hemisphere the whirlpool is located, and in which direction the whirlpool rotates around its axis, the direction of the whirlpool drift depends.

floppy disk

Tilting gyroscope

Experience with a gyroscope

Oceanographers in the middle of the ocean are not actually measuring the height of the tidal wave, but the wave created by the gyroscopic effect of the whirlpool created by precession, the axis of rotation of the whirlpool. And only whirlpools can explain the presence of a tidal hump on the opposite side of the earth. There is no fuss in nature, and if whirlpools exist, then they have a purpose in nature, and this purpose, I believe, is the vertical and horizontal mixing of ocean waters to equalize the temperature and oxygen content in the world's oceans.

And even if lunar tides existed, they would not mix ocean waters. Whirlpools, to some extent, prevent the oceans from silting up. If a couple of billion years ago, the earth actually rotated faster, then the whirlpools were more active. Mariana Trench and the Mariana Islands, I believe the result of the whirlpool.

The tide calendar existed long before the discovery of the tidal wave. Just as there was a regular calendar, before Ptolemy, and after Ptolemy, and before Copernicus, and after Copernicus. Today there are also unclear questions about the characteristics of the tides. So, in some places (South China Sea, Persian Gulf, Gulf of Mexico and Gulf of Thailand) there is only one tide per day. In a number of regions of the Earth (for example, in Indian Ocean) there are sometimes one or two hot tides per day.

500 years ago, when the idea of ​​ebbs and flows was formed, thinkers did not have enough technical means to test this idea, and little was known about eddies in the oceans. And today, this idea, with its attractiveness and plausibility, is so rooted in the consciousness of the public and thinkers that it will not be easy to abandon it.

Why, every year and every decade, on the same calendar day (for example, the first of May) at the mouths of rivers and bays, there is not the same tidal wave? I believe the whirlpools that are located at the mouths of rivers and bays drift and change their size.

And if the cause of the tidal wave was the gravity of the moon, the height of the tides would not change for millennia. There is an opinion that a tidal wave moving from east to west is created by the gravity of the moon, and the wave floods bays and river mouths. But why, the mouth of the Amazon floods well, but the Bay of La Plata, which is located south of the Amazon, does not flood very well, although by all parameters the Bay of La Plata should flood more Amazon.

I believe that a tidal wave at the mouth of the Amazon is created by one whirlpool, and for the La Plata neck of the river a tidal wave is created by another whirlpool, less powerful (diameter, height, revolutions).

Amazon Maelstrom

The tidal wave crashes into the Amazon at a speed of about 20 kilometers per hour, the height of the wave is about five meters, the width of the wave is ten kilometers. These parameters are more suitable for a tidal wave created by the precession of an eddy. And if it were a lunar tidal wave, it would hit at a speed of several hundred kilometers per hour, and the width of the wave would be about a thousand kilometers.

It is believed that if the depth of the ocean was 20 kilometers, then the lunar wave would move as expected at 1600 km.hour, they say that the shallow ocean interferes with it. And now it is crashing into the Amazon at a speed of 20 km.h., and into the Fuchunjiang River at a speed of 40 km.h. I think the math is dubious.

And if the Moon wave moves so slowly, then why in pictures and animations the tidal hump is always directed towards the Moon, the Moon rotates much faster. And it is not clear why, the water pressure does not change, under the tidal hump, at the bottom of the ocean... There are zones in the oceans where there are no ebbs and flows at all (amphidromic points).

Amphidromic point

M2 tide, tide height shown in color. White lines are cotidal lines with a phase interval of 30°. Amphidromic points are dark blue areas where white lines converge. Arrows around these points indicate the direction of the “run around”.An amphidromic point is a point in the ocean where the tidal wave amplitude is zero. The height of the tide increases with distance from the amphidromic point. Sometimes these points are called tide nodes: the tidal wave “runs around” this point clockwise or counterclockwise. The cotidal lines converge at these points. Amphidromic points arise due to the interference of the primary tidal wave and its reflections from the coastline and underwater obstacles. The Coriolis force also contributes.

Although for a tidal wave they are in a convenient zone, I believe in these zones the whirlpools rotate extremely slowly. It is believed that the maximum tides occur during the new moon, due to the fact that the Moon and the Sun exert gravity on the Earth in the same direction.

For reference: a gyroscope is a device that, due to rotation, reacts differently to external forces than a stationary object. The simplest gyroscope is a spinning top. By untwisting the spinning top on a horizontal surface and tilting the surface, you will notice that the spinning top maintains horizontal torsion.

But on the other hand, on a new moon the earth’s orbital speed is maximum, and on a full moon it is minimum, and the question arises which of the reasons is the key. The distance from the earth to the moon is 30 diameters of the earth, the approach and distance of the moon from the earth is 10 percent, this can be compared by holding a cobblestone and a pebble with outstretched arms, and bringing them closer and further away by 10 percent, are ebbs and flows possible with such mathematics. It is believed that at the new moon, the continents run into a tidal hump, at a speed of about 1600 kilometers per hour, is this possible?

It is believed that tidal forces have stopped the rotation of the moon, and now it rotates synchronously. But there are more than three hundred known satellites, and why did they all stop at the same time, and where did the force that rotated the satellites go... Gravitational force between the Sun and the Earth, does not depend on the orbital speed of the Earth, and the centrifugal force depends on the orbital speed of the Earth, and this fact cannot be the reason Lunar tides and low tides.

Calling tides, the phenomenon of horizontal and vertical movement of ocean waters, is not entirely true, for the reason that most whirlpools are not in contact with the ocean coastline... If you look at the Earth from the side of the Sun, whirlpools that are located on the midnight and noon side of the earth are more active because they are in the zone of relative movement.

And when the whirlpool enters the zone of sunset and dawn and becomes edge-on to the Sun, the whirlpool falls into the power of Coriolis forces and subsides. During the new moon, the tides increase and decrease due to the fact that the orbital speed of the earth is at its maximum...