When will the tide ebb at the seaside?

The fluctuation of sea water is regular. If we master the law of tidal fluctuation time, it will bring a lot of convenience to people's daily production and life. There is a way to calculate and master the time of daily tidal fluctuation.

Take Qingdao as an example. The sea area near Qingdao is a regular semidiurnal tide. According to the normal semidiurnal tide, the period of each tidal activity is 12.4 hours, which fluctuates twice a day. In other words, the daily ebb and flow time is about 0.8 hours later than the previous day. Some people sum up the daily climax time as the following two formulas:

From the first day to the fifteenth day of each month, (lunar date-1)×0.8+5 (points); Every month 16 to the end of the month is (lunar date-16)×0.8+5 (points). These two formulas can calculate when the day is the highest tide, the lowest tide time is 6.2 hours later, and the high tide time is 6.2 hours later.

The specific fluctuation time of tides varies from place to place. Mainly depends on the date of the lunar calendar, local tidal types and longitude. If we carefully observe the local tidal law and refer to the above formula, we can calculate the local formula for calculating tidal time.

Extended data

Low tide usually refers to the process of the sea surface falling from high tide to low tide. The cause of low tide is related to both the moon and the sun. When the sea surface drops to the lowest position, the sea surface is in a short-term equilibrium state and the tide stops.

The reason of low tide is related to both the moon and the sun, that is, the tidal force that is often heard comes from the attraction of the moon and the sun to the earth. Tidal-generating force is an integral force, which is not completely determined by the magnitude of gravity, but because the earth is so big, the magnitude and direction of gravity borne by different parts of the earth are not exactly the same, and there are "force difference" and "direction difference", which are two differences that cause tidal-generating force.

The characteristic of tidal force is that the star is stretched along the direction of gravity and compressed in the direction perpendicular to gravity. That's how the tides on the earth come from. It can be seen from the word "stretch" that they are in two directions, so the tides on the earth fluctuate twice a day. Tides caused by the sun are smaller than those caused by the moon, because the moon is much closer to the earth. Moreover, due to the change of the relative position of the sun and the moon, the two tides will overlap each other. When our three stars are in a straight line, there is a climax and a climax, and a "spring tide" appears.

References:

Baidu Encyclopedia: Low tide