Technology The phenomenon of high tides back for this Easter weekend

The phenomenon of high tides back for this Easter weekend

If you are on the Atlantic coast this weekend, you will be able to observe this phenomenon which will continue until Wednesday. A coefficient of 103 is announced, which promises a good show.

300 years BC, the Greek astronomer Pytheas, considered one of the oldest scientific explorers, had already noted a link between the Moon and the height of the tides. At the end of the 17th century, the British mathematician, physicist and philosopher Isaac Newton discovered the theory of gravitation and the phenomenon of high tides became considerably clearer.

“The tides are intimately linked to gravity”, explains Emmanuel Bocrie. The high tides are due to the attraction of the Moon and the Sun on the marine expanses of the Earth. The Moon is certainly smaller than the Sun but it is much closer, and it is estimated that its force of attraction is twice as great. The Moon and the Sun attract the masses of water which move within the oceans, “a bead of water which causes an alternation between high tide and low tide”, explains Emmanuel Bocrie.

The relief of the oceans is not the same everywhere, there are areas of shoals, lowlands, which means that the amplitude of the tides is different from one place to another.
On the Atlantic coasts and those of the Channel, the tide phenomenon is very sensitive but they will be different, from the tip of Brittany to the coasts of the Basque Country. In the Mediterranean, the tides exist but they are very small because the mass of water is less.

The alternation between low tide and high tide takes place every 6 hours. A phenomenon that is explained by the rotation of the Moon around the Earth.

“We have two low tides and two high tides in just over 24:50.”

Emmanuel Bocrie

at franceinfo

To have a large tidal coefficient (on a scale between 20 and 120), the Moon, the Earth and the Sun must be aligned. The phenomenon therefore occurs at different times depending on the rotation of the Earth.

These high tides are more or less important according to the respective positions of the Moon and the Sun with respect to the Earth. When the three are perfectly aligned, the force of attraction on the oceans is maximum, which accentuates the tidal coefficients. The difference in height between high tide and low tide is called “tidal range” and it can vary very significantly depending on where you are.

On the Mediterranean coast, we can record tidal values ​​of 20 or 30 centimeters, but in the bay of Mont-Saint-Michel, we recorded a record of 15 meters 90, the equivalent of a building of 4 to 5 floors. The absolute world record was observed in Canada in the Bay of Fundy, on the Atlantic coast of Canada, at the northern end of the Gulf of Maine, between the provinces of New Brunswick and Nova Scotia. This bay, which is 270km long and about 80km wide, has a particular shape, which amplifies the phenomenon of the tides.

A record was even set at 21.60 meters on the night of October 4 to 5, 1869, when tropical storm Saxby Gale raged with gusts of up to 165 km / h.

In general, the tide coefficients are calculated from the Brest tide. Above 70, we consider that we are in a phenomenon of “white waters”, explains Emmanuel Bocrie, in other words a phenomenon of high tide.
“The coefficient of 103 that we will be able to observe this weekend and in the coming days is quite significant”, assures the forecaster of Météo France.

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