Unique tidal wave March 14th, 2017
In several places on Earth, local landscapes and tides cause a phenomenon called tidal wave. It forms when huge masses of water enter a narrow riverbed.
The 9-meter tidal wave on the Qiantang River in China is recognized as a unique natural phenomenon. At high tide, millions of cubic meters of water, bending around small islands, move against the flow of this river, captivating the views of observers. There are tidal waves in other places, such as Alaska, Brazil (Amazon River) and the longest river in Great Britain, the Severn.
The moment the wave hits the breakwaters on the shore is especially spectacular. But watching this phenomenon is extremely dangerous, and high wave periodically becomes the cause of the death of people watching her. August 22, 2013. (Photo by ChinaFotoPress | ChinaFotoPress via Getty Images):
Sometimes a tsunami is mistakenly called a "tidal wave", but in reality it has nothing to do with tides.
But this does not frighten the extremists. Zhejiang province in eastern China, August 31, 2011. (AP Photo):
The most interesting is the behavior of waves in bays and in "closed" seas, which communicate with the ocean by a narrow strait. In such a sea, its own tidal wave arises - due to the same curvature of the Earth's surface. But such a wave does not have time to form - after all, the weaker the force, the longer it must act to create a large amplitude. Because of not enough large sizes sea, the tide has time to pass from one coast to another, without increasing a significant amplitude.
A tidal wave from the ocean enters these seas. If the depth turns out to be less, the height rises rapidly and the wave speed decreases. Also, the movement of waves is highly dependent on the shape of the coastline. Bay of Fundy, home to the most high tides, wide at the base and tapering sharply towards the mainland. The water is constrained by the shore, for this reason its level also rises. In the White Sea, on the contrary, a tidal wave is scattered on the shores and islands of the elongated sea.
An interesting phenomenon occurs when the tide approaches the mouth of a river that flows into the ocean. When it enters a narrow, and even shallow body of water, the amplitude of the tidal wave increases sharply and a high water wall moves upstream. This phenomenon is called bora.
A tidal wave on the Qiantang River in China, August 31, 2011. About 20 people were injured then. (Photo by Reuters | China Daily):
Upstream: Anchorage, Alaska tidal wave on June 5, 2012. (AP Photo | Ron Barta):
Kayakers catching a tidal wave in Anchorage, Alaska on June 5, 2012. (AP Photo | Ron Barta):
Riding a tidal wave in a canoe in northern Brazil, 12 March 2001. (Photo by AP Photo | Paulo Santos):
Surfers on the River Severn in Gloucestershire, England, March 2, 2010. This is the longest river in the UK. The length of the river is 354 kilometers. (Photo by Matt Cardy | Getty Images):
But back to the extreme in China. A tidal wave on the Qiantang River, August 22, 2013. (Photo by China FotoPress | ChinaFotoPress via Getty Images):
The people like it. A tidal wave on the Qiantang River, August 24, 2013. (Photo by Reuters | Stringer):
(Photo by STR | AFP | Getty Images):
The tidal wave of the Amazon is called vice and is especially powerful during spring floods. At this time of year, good surfers can ride it for a full six minutes. The wave speed of the vice is 35 km per hour, the height can reach six meters. She uproots trees and overturns ships. The width of the tidal wave sometimes reaches 16 km. Sometimes a tidal wave is also called thundering water.
Video: surfing the Amazon.
Also, tidal waves occur in other places. For example, on the Atlantic coast of France, a tidal wave is called mascara, in Malaysia, benak.
You can also note tidal waves on the Pticodyak River in Canada and in Cook Bay, the height of these boars does not exceed two meters.
Remember the cognitive post
British photographer Michael Marten has created a series of original shots that capture the coast of Britain from the same angles, but in different time... One shot at high tide and the other at low tide.
It turned out very unusual, but positive reviews about the project, literally forced the author to start publishing the book. The book, titled "Sea Change", was released in August this year and was released in two languages. It took Michael Marten about eight years to create his impressive series of images. The time between high and low water is on average a little more than six hours. Therefore, Michael has to linger at each location longer than just a few clicks of the shutter.
1. The idea of creating a series of such works was hatched by the author for a long time. He was looking for how to implement changes in nature on film, without human influence. And I found it by chance, in one of the seaside Scottish villages, where I spent the whole day and found the time of ebb and flow.
3. Periodic fluctuations in water level (rises and falls) in water areas on Earth are called ebbs and flows.
The highest water level observed in a day or half a day during high tide is called full water, the lowest level at low tide is called low water, and the moment these limit levels are reached is the standing (or stage), respectively, of high tide or low tide. Average level sea - a conventional 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 the water level during high and low tides are associated with horizontal movements of water masses in relation to the coast. 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 the water level are called ebb and flow. All phenomena associated with ebb and flow are characterized by periodicity. Tidal currents periodically change direction to the opposite, in contrast to them oceanic currents, moving continuously and unidirectionally, are caused by the general circulation of the atmosphere and cover large areas of the open ocean.
4. The ebb and flow of the tide cyclically alternate in accordance with the changing astronomical, hydrological and meteorological conditions. The sequence of the ebb and flow phases is determined by two highs and two lows in the diurnal cycle.
5. Although the Sun plays an essential role in tidal processes, the decisive factor in their development is the force of the Moon's gravitational attraction. 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 are attracted to 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 more the mass of the bodies, the greater the force of mutual attraction arising between them (at the same density, a smaller body will create less attraction than a larger one).
6. 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 greater role in determining the magnitude of the tidal force than the masses of bodies.
The gravitational attraction of the Earth, acting on the Moon and keeping it in near-Earth orbit, is opposite to the Earth's gravity by the Moon, which seeks to displace the Earth towards the Moon and "lifts" all objects on Earth in the direction of the Moon.
The point on the earth's surface located directly under the Moon is only 6400 km away 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 that 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.
7. It is widely believed that water on Earth, located directly under the Moon, rises in the direction of the Moon, which leads to an outflow of water from other places on the earth's surface, however, since the attraction of the Moon is so small compared to that of the Earth, it would not be enough to lift such a huge weight.
Still oceans, seas and large lakes on earth, being large liquid bodies are free to move under the force of lateral displacement, and any slight tendency to lateral displacement 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 crust.
As a result, there is a flow of water from the adjacent areas of the earth's surface towards a place under the moon. The resulting accumulation of water at a point under the Moon creates 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 regions towards a point under the Moon, corresponding ebb tides of water occur at two other points located at a distance equal to a quarter of the Earth's circumference. It is interesting to note that a drop 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.
8. This fact is also explained by Newton's law. Two or more objects located on different distances from the same source of gravity and, therefore, subject to acceleration of gravity of different magnitude, move relative to each other, since the object closest to the center of gravity is most strongly attracted to it.
Water at the sublunary point experiences a stronger attraction to the Moon than the Earth below it, but the Earth, in turn, is more attracted to the Moon than water on the opposite side of the planet. Thus, a tidal wave arises, which is called forward on the side of the Earth facing the Moon, and backward on the opposite side. The first of them is only 5% higher than the second.
9. Due to the rotation of the Moon in its orbit around the Earth between two successive high tides or two low tides in a given location, approximately 12 hours and 25 minutes pass. The interval between the culminations of successive ebb and flow is approx. 6 hours 12 minutes The period of 24 hours 50 minutes between two successive tides is called tidal (or lunar) days.
10. Inequalities in the magnitude of the tide. Tidal processes are very complex, so there are many factors that need to 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) the amplitude of the tide and
3) the type of tidal fluctuations, or the shape of the curve of the course of the water level.
Numerous variations in the direction and magnitude of the tidal forces create a difference in the magnitude of the 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-daily effect. Usually, during the day, due to the main tidal force - the rotation of the Earth around its axis - two complete tidal cycles are formed.
11. If you look from the North Pole of the ecliptic, it is obvious that the Moon revolves around the Earth in the same direction in which the Earth revolves around its axis - counterclockwise. With each subsequent revolution, this point on the earth's surface again takes a position directly under the Moon a little later than during the previous revolution. For this reason, the ebb and flow of the ebb and flow every day are delayed by about 50 minutes. This value is called lunar lag.
12. Half-month inequality. This main type of variation is characterized by a periodicity of about 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 one straight line.
So far, we have only dealt with the tidal effect of the moon. The sun's gravitational field also acts on 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 much greater than the distance to the moon that the tidal force of the sun is less than half the tidal force of the moon.
13. However, when the Sun and the Moon are on the same straight line, both on the same side of the Earth, and on different sides (in the new moon or full moon), the forces of their attraction add up, acting along one axis, and the solar tide is superimposed on the lunar.
14. Likewise, the attraction of the sun intensifies the ebb tide caused by the influence of the moon. As a result, the tides become higher and the ebb tides lower than if they were caused only by the gravity of the moon. Such tides are called syzygy.
15. When the gravitational vectors of the Sun and the Moon are mutually perpendicular (during quadratures, ie, 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.
16. In such conditions, the tides are not so high, and the ebb tides are not as low as if they were due only to the force of the moon's gravity. Such intermediate ebb and flow are called quadrature.
17. The range of elevations of high and low waters in this case is reduced by approximately three times in comparison with the syzygy tide.
18. Lunar parallax inequality. The period of fluctuations in the heights of the tides, arising from the 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 rotation of the latter. 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 the change in the declination of the Moon. When the moon is near celestial equator, two high tides on a given day (as well as two low tides) differ slightly, and the heights of the morning and evening full 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 highest north or south declination, this difference is greatest.
19. Tropical tides are also known, so called because the moon is located almost over the Northern or Southern tropics.
The daily inequality does not significantly affect the heights of two successive low tides in Atlantic Ocean, and even its effect on tide heights is small compared to the overall amplitude of fluctuations. However, in the Pacific Ocean, the diurnal unevenness is manifested in the ebb levels three times more than in the tide levels.
Semi-annual inequality. It is caused by the revolution of the Earth around the Sun and a 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 about a day every half a month. Thus, during the equinoxes, there are periods when the declination of both the Sun and the Moon is approximately 0. The total tidal effect of the attraction of these two bodies at such moments is most noticeably manifested in regions located near the Earth's equator. If at the same time the Moon is in the phase of a new moon or a full moon, the so-called. equinox syzygy tides.
20. Solar parallax inequality. The period for this inequality is one year. It is caused by the change in the distance from the Earth to the Sun during the Earth's orbital motion. Once for each revolution around the Earth, the Moon is at the 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, more high levels tides and more low levels ebb tides. Likewise, if the passage of the aphelion coincides with the apogee, less high tides and shallower ebb tides occur.
21. The largest amplitudes of tides. The world's highest tide occurs with strong currents in Minas Bay in the Bay of Fundy. The tidal fluctuations here are characterized by a normal course with a semidiurnal period. The water level during high tide often rises by more than 12 m in six hours, and then decreases by the same amount over the next six hours. When the effect of syzygy tide, the position of the Moon at perigee and the maximum declination of the Moon fall on one day, the tide level can reach 15 m. the top of the bay. The reasons for the tides, being subject constant study for many centuries, refer to the problems that have given rise to many conflicting theories even in relatively recent times
22. Charles Darwin wrote in 1911: “There is no need to search antique literature for the sake of grotesque theories of tides ”. However, sailors manage to measure their height and use the possibilities of tides without knowing the real reasons for their occurrence.
I think that we also need not bother especially about the causes of the origin of tides. Based on long-term observations, special tables are calculated for any point in the water area of the earth, which indicate the time of high and low water for each day. I am planning my trip to, for example, Egypt, which is just famous for its shallow lagoons, but try to guess in advance so that full water falls in the first half of the day, which will allow most daylight hours to fully ride.
Another tide-related issue of interest to the kiter is the relationship between wind and water level fluctuations.
23. Folk omen claims that at high tide the wind increases and at low tide, on the contrary, turns sour.
The effect of wind on tidal phenomena is clearer. The wind from the sea drives the water towards the coast, the tide height increases above normal, and at low tide the water level also exceeds the average. On the contrary, when the wind blows from the land, the water is driven away from the coast, and the sea level drops.
24. The second mechanism works by increasing atmospheric pressure over a wide area, the water level drops as the superimposed weight of the atmosphere is added. When atmospheric pressure rises by 25 mm Hg. Art., the water level drops by about 33 cm. Zone high pressure or anticyclone is usually called good weather, but not for a kiter. Calm in the center of the anticyclone. A 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 the water level. Such waves, although called tidal waves, are not actually 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 affect the wind, for example, a decrease in the water level in coastal lagoons, leads to greater heating 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.
In several places on Earth, local landscapes and tides cause a phenomenon called tidal wave. It forms when huge masses of water enter a narrow riverbed.
The 9-meter tidal wave on the Qiantang River in China is recognized as a unique natural phenomenon. At high tide, millions of cubic meters of water, bending around small islands, move against the flow of this river, captivating the views of observers. There are tidal waves in other places, such as Alaska, Brazil (Amazon River) and the longest river in Great Britain, the Severn.
The moment the wave hits the breakwaters on the shore is especially spectacular. But watching this phenomenon is extremely dangerous, and a high wave periodically becomes the cause of the death of people watching it. August 22, 2013. (Photo by ChinaFotoPress | ChinaFotoPress via Getty Images):
Sometimes a tsunami is mistakenly called a "tidal wave", but in reality it has nothing to do with tides.
But this does not frighten the extremists. Zhejiang province in eastern China, August 31, 2011. (AP Photo):
The most interesting is the behavior of waves in bays and in "closed" seas, which communicate with the ocean by a narrow strait. In such a sea, its own tidal wave arises - due to the same curvature of the Earth's surface. But such a wave does not have time to form - after all, the weaker the force, the longer it must act to create a large amplitude. Due to the insufficiently large size of the sea, the tide has time to pass from one coast to another, without increasing a significant amplitude.
A tidal wave from the ocean enters these seas. If the depth turns out to be less, the height rises rapidly and the wave speed decreases. Also, the movement of waves is highly dependent on the shape of the coastline. The Bay of Fundy, home to the highest tides, is wide at its base and tapers sharply towards the mainland. The water is constrained by the shore, for this reason its level also rises. In the White Sea, on the contrary, a tidal wave is scattered on the shores and islands of the elongated sea.
An interesting phenomenon occurs when the tide approaches the mouth of a river that flows into the ocean. When it enters a narrow, and even shallow body of water, the amplitude of the tidal wave increases sharply and a high water wall moves upstream. This phenomenon is called bora.
A tidal wave on the Qiantang River in China, August 31, 2011. About 20 people were injured then. (Photo by Reuters | China Daily):
Upstream: Anchorage, Alaska tidal wave on June 5, 2012. (AP Photo | Ron Barta):
Kayakers catching a tidal wave in Anchorage, Alaska on June 5, 2012. (AP Photo | Ron Barta):
On a tidal wave in a canoe in northern Brazil, March 12, 2001. (AP Photo | Paulo Santos):
Surfers on the River Severn in Gloucestershire, England, March 2, 2010. This is the longest river in the UK. The length of the river is 354 kilometers. (Photo by Matt Cardy | Getty Images):
But back to the extreme in China. A tidal wave on the Qiantang River, August 22, 2013. (Photo by China FotoPress | ChinaFotoPress via Getty Images):
The people like it. A tidal wave on the Qiantang River, August 24, 2013. (Photo by Reuters | Stringer):
(Photo by STR | AFP | Getty Images):
The tidal wave of the Amazon is called vice and is especially powerful during spring floods. At this time of year, good surfers can ride it for a full six minutes. The wave speed of the vice is 35 km per hour, the height can reach six meters. She uproots trees and overturns ships. The width of the tidal wave sometimes reaches 16 km. Sometimes a tidal wave is also called thundering water.
Video: surfing the Amazon.
Also, tidal waves occur in other places. For example, on the Atlantic coast of France, a tidal wave is called mascara, in Malaysia, benak.
You can also note tidal waves on the Pticodyak River in Canada and in Cook Bay, the height of these boars does not exceed two meters.
The gravitational influence of the Sun and the Moon affects all shells of the Earth - air, water and earth, despite the huge distances separating them from the Earth. Note that the very concept of gravity as a physical factor became known only to mid XVII c "when this term was introduced by the great physicist Isaac Newton. Then, after numerous works of scientists different countries, performed in the XIX and LX centuries., became clear physical foundations gravitational influence to the Earth of the Moon and the Sun. This influence, both direct and indirect, is very diverse. The most significant of them are oceanic tides, different in scale and amplitudes in different geographic points of the Earth [Maksimov IV et al., 1970; Carter S., 1977; Marchuk G. And Kagan B.A., 1983; Bouteloup J., 1979]. For millennia, people have watched tides and ebb and were convinced of their close connection with the phases of the moon and the conjugation of changes in environment with the time of the onset of these phases, centuries-old observations led scientists to the conclusion about the important significance of the moon for natural processes and about her significant impact per person: through the ozone layer, geomagnetic activity, precipitation. "Our exploration of the Moon, our future, may largely depend on a deeper understanding of the tidal action of the Moon on the Earth" [Carter S., 1977].
Most interesting moment in the whole problem of tides is the fact that a grandiose in its scale process, covering the entire Earth, all its shells, is caused by fluctuations in gravity that are negligible in magnitude (Fig. 4). Suffice it to say that as a result of lunar-solar attraction, the body weight, for example, one ton, changes by only 0.2 g. The magnitude of the change in gravity can be judged by the following figures: the acceleration of gravity on Earth is 982.04 cm / s ^ (g = 982.04 gal), and the maximum change due to the influence of the Moon and the Sun is only 240.28 μgal (or 0.24 mlgal), i.e. 100-thousandths of a percent of g. And of them 164.52 mgal falls on the action of the moon and 75.76 mgal - on the share of the gravitational influence of the sun. These negligible gravitational forces are sufficient to set in continuous motion billions of tons of water, earth's solidity and air masses.
Tidal phenomena occur due to the combined gravitational action of the Moon and the Sun on the Earth. The greatest influence is exerted by the Moon, which, despite its incommensurably small size in comparison with the Sun, is at a distance closer to the Earth (356,000 km) than the Sun (150-10 ^ km). Sea and ocean ebb and flow, repeating 2 times a day, are easily visible to the observer by the periodic rise and fall of the water level in the coastal areas. The relative position of the Earth, Moon and Sun in outer space changes all the time and therefore the magnitude of the tides also changes. It is determined using instruments that measure the height of the water surface during high tides.
The tides reach their maximum in the new moon and full moon (syzygy tides, from the Latin word "syzygy" - conjunction) when the Moon and the Sun are in a straight line with the Earth. The minimum tides, called quadrature (from the Latin word "quadrature" - quarter), are observed in the phase of the first and last quarter of the Moon, when the difference in astro-longitudes of the Moon and the Sun is 90 °, that is, they are located at right angles to each other (Fig. 5).
Less known terrestrial and atmospheric tides [Melchior P., 1968; Chapman S., Lindzen P., 1972], which are not as obvious as oceanic and marine, but they also have a global scale. So, in the upper mantle of the Earth, in the very outer shell crust, the gravitational force of the Moon and the Sun causes periodic rises and falls of the surface, observed with the help of gravimeters that measure local changes in the force of gravity. Under the influence of the Moon, the Earth's surface rises by a maximum of 35.6 cm and falls by 17.8 cm, while the Sun causes the surface to oscillate, respectively, up to 16.4 cm and down to 8.2 cm. Overall size lunisolar oscillations of the earth's surface is 78 cm: under the influence of the Moon by 53.4 cm and the Sun by 24.6 cm.
This is a kind of "breathing" of the Earth - the movement of its surface under the influence of gravitational forces. As noted above, these tremendous in scale movements of water and earth layers occur under the influence of negligible gravitational influences, constituting millionths of the modulus of the earth's gravity. Continuous movement of the earth's surface leads to big changes in the structure of the earth's crust, the speed of rotation of the Earth around its axis, the parameters of orbital motion and other geophysical phenomena (in particular, to continental drift, shift of oceanic plates, an increase in faults and even the frequency of earthquakes occurring).
Large-scale changes also occur in the atmosphere under the influence of the gravitational influence of the Moon and the Sun, further intensified by its periodic heating from the Sun. The indicator of atmospheric tides is the change in air pressure measured by a barometer. It should be remembered that the tidal force arising from the gravitational influence of the Moon and the Sun at any point in each of the Earth's shells is continuously changing due to the rotation of our planet and a number of other factors. However, the characteristic wave itself remains during the day, only transforming in shape and amplitude depending on the geographical latitude of the place. In the structure of this wave there are two main components - lunar and solar, in which, using the method of harmonic analysis, several components are identified: long-term (weekly and monthly) and short-period (daily, semidiurnal and third-day) [Marchuk G. I., Kagan B. A ., 1983].
For the subsequent biomedical analysis of the influence of the Moon, not only the entire fine structure of the spectrum of lunar waves and half waves is important, but mainly the presence of short- and long-term components that determine the biorhythm of living organisms. For example, when analyzing circadian biorhythmics, it is important for researchers to know that in tidal phenomena there is a dominant semidiurnal wave (Ma) with a period of 12 h 25 min, corresponding to a semidiurnal tide, and a solar tidal wave (82) with a period of 12 h 00 min. The long-term components, monthly and bi-weekly, have a period of 27.555 and 13.661 days, respectively. These periods are important, as they are manifested in the biorhythmics of various processes in the body, thereby indicating the possible role of gravitational tidal forces as an external synchronizer [Brown F "1964, 1977; Howenshield K., 1964; Vasilik P. V., Galitsky A. K ., 1977, 1979; Chernyshev VB, 1980; Neiman D "1984; Garzino S., 1982a; Brown F. A., 1983].
The tides associated with the action of the gravitational forces of the Moon and the Sun are extremely diverse in different geographical points of the Earth, which depends on many physical factors... But when considering their diurnal dynamics, 3 main types can be distinguished - diurnal, semi-diurnal and mixed, or combined [Marchuk G. And "Kagan AB, 1983; Neiman D" 1984].
Daily tides occur once a day and are caused by the action of two components of the tidal force with periods of 25.8 and 23.9 hours. In a number of places the globe(for example, off the coast of Mexico) in the dynamics of diurnal tides every 13-14 days (on average 13.66 days) there is a 180 ° phase shift correlating with 1/2 of the Moon declination cycle (recall that tropical moon month is equal to 27.32 days), i.e., with the crossing of the Moon every 13.66 days of the plane of the celestial equator. Here you can clearly see how the movement of our satellite in space causes regular changes in geophysical processes.
Semi-daily hot flashes are noted 2 times a day with a period of 12.4 hours. Their amplitude varies during synodic month(29.53 days) from maximum value full moon and new moon to minimum in different quarters of the moon. Changes in amplitudes constitute a semi-synodic cycle corresponding to the change lunar phases... Syzygy tides are repeated every 14-15 days (average 14.76 days). Mixed (combined) tides have different amplitudes of water rise and differ in unequal periods - they are observed off the coast The Pacific, Australia, Arabian Peninsula. We deliberately dwell on the types of tidal rhythms, since tidal and lunar rhythms are subdivided in biology [Chernyshev VB 1980; Neiman D., 1984]. As the cited authors point out, there are endogenous rhythms with peaks of activity repeating every 12.4 hours. They lend themselves to capture by tidal cycles ("near-tidal" rhythms) and most of them do not differ in the stability and accuracy inherent in circadian rhythms [Neumann D., 1984, with. 12].
In addition, it has been noted that some species may have a double tidal rhythm of 24.8 hours. This is due to adaptation to the local tidal profile. Research shows that perception of tidal factor during the daily sensitive phase is related to and dependent on circadian rhythm. Tidal rhythms can also be modulated by diurnal light cycles and semi-monthly tidal components, resulting in complex rhythms in specific species living in specific environmental conditions... At the same time, different types lunar rhythms associated with direct action are observed moonlight and the change of lunar phases (syzygy and synodic rhythms). These rhythms can be traced in aquatic and terrestrial species regardless of tidal cycles [Chernyshev VB, 1980; Neumann D "1984]; their features are discussed below.
Excitement is a form of periodic, continuously changing motion in which water particles vibrate around their equilibrium position.
If, for any reason, the water particles are removed from the equilibrium position, then under the influence of gravity they will tend to restore the disturbed equilibrium. Moreover, each water particle will perform an oscillatory motion relative to the equilibrium position, without moving along with the visible form of wave motion.
Waves can arise under the influence of various reasons (forces). Depending on the origin, that is, on the causes that caused them, distinguish the following types sea waves.
- Friction waves (iln frictional). These waves include, first of all, wind waves that arise when the wind acts on the sea surface. They also include the so-called internal, or deep, waves that arise at depths when a layer of water of one density moves over a layer of water of a different density.
- Baric waves occur when atmospheric pressure fluctuates. Oscillations of atmospheric pressure cause the rise and fall of water masses, in which water particles tend to take new equilibrium positions, but, having reached them, perform oscillatory movements by inertia.
- Tidal waves occur under the influence of the phenomenon of ebb and flow.
- Seismic waves are generated during earthquakes and volcanic eruptions. If the source of an earthquake is located under water or close to the coast, then the vibrations are transmitted to the water masses, causing them to seismic waves, which are also called tsunamis.
- Seiches. In seas, lakes, reservoirs, in addition to oscillations of water particles in the form of forward waves, periodic oscillations of water particles only in the vertical direction are often observed. Such waves are called seiches. With seiches, vibrations occur, similar in nature to vibrations, in a periodically swayed vessel. The simplest type of seiche occurs when the water level rises at one end of the reservoir and simultaneously drops at the other. In this case, a line is observed in the middle of the reservoir along which water particles do not have vertical displacements, but move horizontally. This line is called a seiche node. More complex seiches are two-node, three-node, etc.
