Tidal water

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Tide, yes ocean Medium and coastal areas Of rivers Moderately affected tide On a regular basis Fluctuation Water.

Chinese name: Tidal water
Foreign name: The tide
Tide: Fluctuation of sea water

tide: Seawater fluctuation during the day
Xi: Nocturnal fluctuation
Works: Preface to Ocean Tide Map

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Causes

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Tide picture

Moon Gravity and Earth centrifugal force It is two opposite forces. The resultant force (vector sum) generated by the combination of the two forces is the force that the moon causes the tide phenomenon in the sea water, which is called the lunar tidal force. The tide generated by the lunar tidal force is called Lunar tide ； The mass of the sun is about 27 million times the mass of the moon, and the average distance from the sun to the earth is about 389 times the average distance from the moon to the earth. Therefore, it can be calculated that the ratio of the solar and lunar tidal forces is 1:2.18. sunlight Tidal force Tidal phenomenon caused by（ Diurnal tide ）Although it is not easy to be observed alone, it affects the magnitude of the moon tide.

Every time on the first day of the lunar calendar (New Year) or the fifteenth day of the lunar calendar (Looking), the positions of the earth, the moon and the sun are almost in the same straight line. The tidal forces of the moon and the sun are the same. When the two forces are combined, the sea water will appear spring tide. But every time on the seventh or eighth day of the lunar calendar (the first chord) or on the twenty second or third day of the lunar calendar（ Bottom chord ）When the tide generating force of the moon on the earth is perpendicular to that of the sun on the earth, the sun's tide generating force weakens the moon's tide generating force, so the sea water appears Neap tide 。

In fact, spring tide often occurs in Outlook In the last two or three days, the neap tide mostly occurs in the last two or three days after the upper and lower chords, because the sea water is affected by its own Viscosity and Submarine topography Caused by the influence of factors.

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Tidal water

The diurnal fluctuation of sea water is called tide , fluctuations at night are called Xi , so the fluctuation of sea water is also called tide 。 Tide phenomenon refers to that the sea water celestial bodies (Mainly Moon and sunlight ） Tidal force The periodic motion generated by the action occurs with the relative position of the earth, moon and sun Periodic change The action of this force also changes periodically. Thus, this periodic tide phenomenon appeared in front of people.

There is an ancient book "Preface to the Tide Map" in China“ sea It is recorded that the water in the morning is the tide, and the water in the evening is the tide.

Formation process

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tide When the tide level keeps rising and reaches a certain height, Tidal level It is called flat tide if it does not rise or recede in a short time, and the middle time of flat tide is called At high tide 。 The duration of flat tide varies from several minutes to tens of minutes. After the flat tide, the tide level begins to decline.

Tidal water

When the tide level recedes to the lowest, similar to the flat tide, the phenomenon that the tide level does not recede or rise also occurs, which is called Ceasing tide And its intermediate time is At low tide 。

After the tide stopped, the tide level began to rise again, moving again and again. From low tide to high tide time interval be called At high tide The time interval from high tide to low tide is called At ebb tide 。

Generally speaking, the time of rising tide is not the same as that of falling tide in many places. The height when the sea surface rises to the highest position is called the high tide height, and the height when it drops to the lowest position is called the low tide height. The difference between the adjacent high tide height and the low tide height is called Tidal range 。

type

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In a Tidal period (Approx 24 hours 50 minutes, astronomy calls one Lunar day , i.e Moon The times, times and duration of tide fluctuation are also different in different places. Although the tide phenomenon is very complex, there are three basic types.

Semidiurnal tide Type: There are two high tides and two low tides in one lunar day Tidal range The tidal range is roughly the same as that of the next high tide and low tide, tide The time of the process and ebb tide process is almost the same (6 hours and 12.5 minutes). our country the bohai sea 、 The East China Sea 、 Yellow Sea Most of the locations are half a day Tidal pattern , such as Dagu 、 Qingdao 、 Xiamen Etc.

Diurnal tide Type A: There is only one high tide and one low tide in a lunar day. as South China Sea Shantou 、 the bohai sea qinghuangdao Etc. South China Sea Beibu Gulf It is a typical diurnal tidal sea area in the world.

Mixed tide Type: There are two high tides and two low tides on some days in a month, but the tidal range between the two high tides and low tides is quite different, and the time of rising tide process and falling tide process is also different; On other days, there was a high tide and a low tide. Most places in the South China Sea belong to mixed tide type. as Yulin , the diurnal tide appears in 15 days, and the other days are irregular Semidiurnal tide ， Tidal range Larger.

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