Ocean Tides – what causes ocean tides – 2021

ocean tides…….Ebb and flow, periodic fluctuations in the level of the ocean (sea), as well as the celestial body itself, caused by the influence of external (so-called tide-forming) bodies. The periods of oscillations are determined by the periods of revolution of the tidal bodies relative to the celestial body under consideration.

Tidal forces

Tidal B-ly arises due to inhomogeneities of gravity. fields: the elements of mass located closer to the tidal body experience a greater attraction to it and therefore are shifted towards it somewhat more than the more distant ones. As a result, the celestial body tends to stretch along the straight line connecting it with the tidal body. For an observer on a celestial body, tidal forces are directed upward when the tidal body is at its zenith or nadir, and down ward when it is on the horizon.

Fig. 1. Location of celestial bodies at syzygy (a) and quadrature (b) tides: S – Sun, W – Earth, L – Moon.

On Earth, the tides cause in DOS. The Moon and the Sun (respectively, the lunar and solar tides), and the height of the lunar tide is approximately 2 times greater than the solar one. Allocate the so-called. the syzygy tide, which occurs on the days when the Earth, the Moon and the Sun lie approximately on the same straight line (Fig. 1, a ), and the quadrature tide, at which the directions to the Moon and the Sun form a right angle (Fig. 1, b ). With a syzygy tide, the influence of the Sun enhances the influence of the Moon, and with a quadrature tide, it weakens. As a result, the height of the syzygy tide is approximately three times the height of the quadrature tide.

Ocean ebb and flow

Fig. 2. Syzygy high tide (1) and low tide (2) in the Kandalaksha Bay of the White Sea.Photo by O. A. Bochkova

Ocean ebb and flow cause water movements called tidal currents. The typical period of oceanic waves P. and about. approximately 12 hours 25 minutes, length – half the circumference of the Earth, approx. 20038 km. A tidal wave, propagating, meets obstacles in the form of continents, islands, experiences friction against the bottom, ebb currents arise; as a result of all this, the distribution of amplitudes and phases of the dec. tidal waves are extremely different from theoretical. quantities, for example. in int. seas P. and about. insignificant. P.’s size and character and about. depend not only on the relative position of the Earth, the Moon and the Sun but also on the geographic. latitude, depth of the reservoir and the shape of the coastline. A dynamic theory of P. and o., based on the general equations of hydrodynamics, La p la catfish.

The highest water rise in the World approx. called complete in-doy, minimum – small in-doy. The time interval between adjacent high or low waters is called the tidal period. Depending on the period, there are daily, semi-daily and mixed tides (irregular semi-daily and irregular daily). In the ocean, far from the continents, the size of P. and about. of the order of 1 m, near the coast, the difference between consecutive full and low water can reach large values. So, into the hall. Fan di highest value P. and. reaches 18 m (according to other data, 16 m), in the hall. Frobisher on about. Baffin’s Land and in some points of the Strait. English Channel – up to 15 m, inPenzhina gu-baa Okhotsk m -.. To 12.9 m Tidal wave penetrating into the mouth of a river can cause a steep wave (see. In ro-ro-ka ). At low tide, vast areas of shallow waters with numerous. inhabitants of the seabed, fishing objects of the local population. P.’s energy and about. is used to generate electricity in tidal elec-tro-mill-chi-s .

The distribution of tidal waves in the open ocean is determined by the hydrodynamic solution. differential Laplace equations. To ensure the navigation, “Tide Tables” are published, containing data on the tide height in important ports for every hour throughout the year. As a result of solving the equations, cotidal maps of the World ok. Are created, on which some isolines (so-called cotidal lines) connect the points of the wave with the same phase, for example. the position of the maximum of this wave every hour, and the others are points with the same amplitude of this wave.

Earth tides

Tidal forces act not only on the waters of the oceans but also on all elements of the mass of the planets. Fluctuations in the Earth’s body (offset level is the top-but-sti ) called terrestrial tides. Precision data earth tides were prepared by cryogenic gra-vi-meth-ditch and radio interferometers long baseline. The vibration amplitude of the level surface is approx. 0.5 m.

In 1863, W.  Tom-son (Lord Kelvin) suggested the idea of the possibility of determining the average hardness of the globe with the help of the study of earth tides. If the Earth were a molten body covered with a relatively thin crust, then the tidal displacements of the earth’s surface would almost exactly coincide with the tidal displacements of the level surface, i.e., oceanic. hot flashes should not have been observed. Thus, the very fact of the existence of oceanic. tides indicate that the thickness of the Earth’s rigid shell, under any reasonable assumptions about its rigidity, amounts to hundreds or thousands of kilometres. This estimate was later confirmed (with the development of seismology).

Despite the fact that the attitude cf. the depth of the oceans to the radius of the Earth is less than 1/1000 (and this means that part of the Earth’s volume falls on the liquid core, the viscosity of which is comparable to the viscosity of seawater), the absorption of tidal energy in the Earth’s body is only approx. 3% of its absorption in the ocean. This is due to the closeness of the periods of free ocean oscillations to tidal periods. In addition, due to the high pressure in the bowels of the Earth, mechanical. shell properties differ little from mechanical. properties of an ideally elastic body, which also leads to a small absorption of tidal energy in the Earth’s mass.

Influence of tides on the movement of celestial bodies

Tidal forces play a decisive role in slowing down the diurnal rotation of planets and their satellites. The absorption of tidal energy in the oceans of the Earth leads to a secular slowdown in its daily rotation (the length of the day increases by about 2 ms in 100 years), as well as to a secular distance of the Moon from the Earth (about 4 cm per year). For theoretical. the calculation of these effects uses the detailed altimetry obtained from the satellite. data on the heights of the ocean. tides.

The tidal energy absorbed by the Earth is negligible compared to the energy received by the Earth from the Sun. However, for the Galilean satellites, It is the tidal energy of Jupiter that plays a decisive role: due to the tidal slowdown of the diurnal rotation, all Galilean satellites in the present time. epoch is turned to Jupiter on one side (similar to how the Moon is turned to Earth). Due to the ellipticity of the orbits of the satellites and their gravity. interactions with each other The distances from the Galilean satellites to Jupiter and their orientation relative to Jupiter change slightly. These changes are sufficient for the release of thermal energy in the bowels of the satellites, significantly exceeding the energy they receive from the Sun. Due to tidal effects in the bowels of Jupiter’s moon Io, energy is released on the order of (6–8) · 10 13 W, which corresponds to a heat flux on the surface of approx. 2 W / m 2(this is 30 times the heat flux released through the Earth’s surface). As shown by observations from the spacecraft of the “Voyager” series (NASA), dep. parts of the surface of Io, due to the absorption of tidal energy, are heated to a temperature of the order of 300–600 K. Volcanic activity was recorded in these areas. activity. The total area of ​​such plots is approx. 2% of the total surface area of ​​the satellite. The surface of Jupiter’s moon Europa is a cracked crust of water ice from several kilometres to several hundred kilometres thick. Beneath it is believed to be an ocean of water. The tidal energy released in the bowels of Europa is significantly less than the same energy on Io,

The atmospheres of the Earth and other planets are observed periodically. changes in atmospheric pressure called tides. However, these hot flashes are caused by preim. periodic fluctuations of solar thermal radiation (and not the gravitational influence of other celestial bodies): the dayside of the planet receives more energy than the night side. Thermal expansion of air leads to fluctuations in atmospheric pressure and to cyclic. displacement air. masses with periods that are multiples of solar days.

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