Are the global tides (high tides) twice a day? When are they different? How long can it last?

Tide is a general term for the periodic movements and changes that occur in the Earth's lithosphere, hydrosphere and atmosphere due to the tidal forces of the sun and moon. The elastic-plastic deformation of the solid earth caused by the tidal force of the sun and the moon is called solid tide, referred to as the solid tide or ground tide; the periodic rise and fall, rise and fall, advance and retreat of the sea surface caused by the tidal force of the sun and the moon by sea water, It is called ocean tide, or ocean tide for short; the periodic changes (such as 8, 12, 24 hours) caused by the tidal force of various elements of the atmosphere (such as air pressure field, atmospheric wind field, earth magnetic field, etc.) are called atmospheric tide, or air tide for short. . Among them, the atmospheric tides caused by the sun are called solar tides, and those caused by the moon are called lunar tides. Because the moon is closer to the earth than the sun, the ratio of the tidal forces of the moon and the sun is 11:5. For the ocean, the lunar tide is more significant than the solar tide. The driving forces of earth tides, ocean tides and air tides are all caused by the different gravitational forces of the sun and the moon on various parts of the earth, and the three influence each other. The elastic-plastic tidal deformation of the crust at the bottom of the ocean will cause corresponding ocean tides, that is, there is an impact of the ground tide effect on ocean tides; and the migration of seawater mass caused by ocean tides changes the load on the earth's crust, causing the earth's crust to undergo sustainable changes. Complex changes. The air tide is above the ocean tide, and it acts on the sea surface to cause additional vibrations, making the changes in the ocean tide more complicated. As a complete tidal science, its research objects should be ground tides, ocean tides and air tides as a unified whole. However, because the phenomenon of ocean tides is very obvious and closely related to people's lives, economic activities, transportation, etc., it is customary to treat tides as The word (tide) is understood in a narrow sense as ocean tide.

Tide is a natural phenomenon in coastal areas. In ancient times, the tide during the day was called "tide", and the tide at night was called "tide". Together, it is called "tide". Its occurrence is related to the sun and the moon. It has something to do with it, and it also corresponds to our country’s traditional lunar calendar. On the first day of each month in the lunar calendar, the sun and moon are on one side of the earth, so they have the greatest tidal force, causing "spring tides". Around the fifteenth or sixteenth day of each month in the lunar calendar, the sun and the moon are on both sides of the earth, the tidal force of the sun and the moon will also cause "spring tides" when you push and pull them; when the moon phase is in the first quarter and last quarter, that is, on the eighth and twenty-third o'clock of the lunar calendar, the tidal force of the sun and the moon will The tidal forces partially offset each other, so a "neap tide" occurs. Therefore, there is a saying in the farmer's proverb that "the tide rises on the 15th day of the lunar month, and there are beaches everywhere on the 8th and 23rd day of the lunar month." In addition, high tides also occur on the first day. Since the moon moves more than 13 degrees eastward on the celestial sphere every day, the total time is about 50 minutes. That is, the moon's zenith time (1 lunar day = 24:50) is delayed by about 50 minutes every day. (Tides can also occur in the middle of the day, and there are usually two tides every day.) Therefore, the time of high tide is also delayed by about 50 minutes every day.

However, due to the complexity of the movement of the moon and the sun, the spring tide may sometimes be delayed by a day or several days, and the high tide during a lunar day is often one hour or more behind the moon's superior or inferior celestial phase. For several hours, a tide occurs in some places on a lunar day.

The gravity of the sun and the moon has such a great effect on the water (liquid) on the earth, and it also affects the solid continents of the earth's crust, causing "land tides". "Land tides" may cause earthquakes, so The moon phase should be taken into consideration when making earthquake predictions.

The gravity of the sun and the moon will also have a great effect on the atmosphere (gas) on the earth, causing "atmospheric tides", causing changes in atmospheric convection and atmospheric motion, and causing changes in climate. (This is contrary to the traditional view that climate change has nothing to do with the moon.) Therefore, meteorological experts recommend that the moon phase should be considered when making weather forecasts.