How long is the general high tide and low tide?

The time of high tide and low tide is different in different areas. For most parts of China, it belongs to semi-diurnal tide type. Generally, the high tide and low tide are twice a day, and the high tide time is from early morning to noon, and the low tide time is generally 6 hours after the high tide, and it is circulated twice a day.

The Bohai Sea, the East China Sea and the Yellow Sea in China are mostly semi-diurnal tides. In a tidal cycle (about 24 hours and 50 minutes, known as lunar day in astronomy, that is, the time required for the moon to pass through the transit twice in a row), the number, time and duration of tidal fluctuations vary from place to place.

The regular semidiurnal tide fluctuates once every 12 hour.

The simple calculation method of tidal time is: maximum tidal time = lunar calendar ×0.8, minimum tidal time = maximum tidal time +/-6.

Suppose: today is 15 of the lunar calendar, and the highest climax time is = 15×0.8= 12, that is,12 at noon and midnight; The lowest ebb time is 6 am and 6 pm. Close observation time is from 4: 00 am to 8: 00 am and from 4: 00 pm to 8: 00 pm.

Extended data

In a tidal cycle, the number, time and duration of tidal fluctuations vary from place to place. Although the tidal phenomenon is complex, it can be roughly divided into three basic types.

1, semidiurnal tide type

A lunar calendar day has two high tides and two low tides. The tidal range of the first high tide and low tide is almost the same as that of the last high tide and low tide, and the time of high tide and low tide is almost the same (6 hours 12.5 minutes). The Bohai Sea, the East China Sea and the Yellow Sea are semi-diurnal tides in most parts of China, such as Dagu Lake, Qingdao and Xiamen.

2. All-day tidal type

A solar day has only one high tide and one low tide. For example, Shantou in the South China Sea and Qinhuangdao in the Bohai Sea. Beibu Gulf in the South China Sea is a typical diurnal tide area in the world.

3. Mixed tidal model

On some days in January, there are two high tides and two low tides, but the tidal range between the two high tides and low tides is very different, and the time of high tides and low tides is not equal. On other days, there are high tides and low tides. Most of the South China Sea in China belongs to mixed tidal type. For example, in Yulin Port, there is a diurnal tide on 15 days, and the other days are irregular semidiurnal tides with large tidal range.

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