Time: from August 16 to August 18 in the lunar calendar, the sun, the moon and the earth are almost in a straight line, so the tidal force (the difference between the gravity of the moon, the sun or other celestial bodies on the earth and the gravity of the geocentric unit mass objects, or the resultant force of the inertial centrifugal force generated by the movement of the earth around the center of mass of the moon (sun) and the moon (sun).
Geographical location: It is related to the trumpet-shaped estuary of Qiantang River. On the south bank of Qiantang River, nearly 500,000 mu of land was reclaimed to the east of Zheshan Mountain, which blocked the estuary like a peninsula, making the section from Zheshan Mountain to the outside of Qiantang River 12 km look like a bottle with a small belly, and the tide is easy to enter but difficult to retreat. The outer mouth of Hangzhou Bay is 100 km wide, and it is only a few kilometers wide to the outer 12 sections. The riverbed in the east of the estuary suddenly rises and the beach is shallow. When a large number of tides flood in from the mouth of Qiantang River, due to the rapid contraction of the river,
Secondly, it is related to the sediment deposition under the Qiantang River, which blocks and rubs the tidal current, making the front slope of the tidal current steep and gentle, thus forming a wave after catching up with the front wave, and one wave overlaps with another.
Wind direction: the southeast wind is often blown along the coast, and the wind direction is generally consistent with the tidal direction, which is helpful for the tidal direction.
Extended data:
Qiantang River is located in Zhejiang Province, China, and finally flows into the East China Sea. Its mouth tide is qiantang bore, which is famous all over the world. Many tourists come to see this spectacle every year.
Historical origin
Watching autumn tide in Qiantang has become a custom as early as the Han, Wei and Six Dynasties, especially in the Tang and Song Dynasties. According to legend, August 18 of the lunar calendar is the birthday of the tide god, so the tide peak is the highest. In the Southern Song Dynasty, the imperial court stipulated that the navy division should be inspected on the Qiantang River on this day. Later, they became accustomed to each other, and August 18 gradually became a tide-watching festival. Pan Lang, a poet in the Northern Song Dynasty, wrote in Jiuquanzi:
Long memories of watching the tide, full of people vying to see the river. I suspect that the sea is empty and drums are beating all around. Xiang Tao, the frolic in the frolic, stands upright and keeps the red flag wet. I don't see the dream a few times, but I am still chilling.
This poem is a true portrayal of the activities of "making waves" and "watching the tide" in those years.
References:
Baidu encyclopedia-Qiantang chamber