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The second strongest tidal constituent "S 2" is influenced by the sun, and its Doodson numbers are 273.555, meaning that its frequency is composed of twice the first Doodson argument, +2 times the second, -2 times the third, and zero times each of the other three. [50] This aggregates to the angular equivalent of mean solar time +12 hours.
Tidal waves are not perfectly reflected, resulting in energy loss which causes a smaller reflected wave compared to the incoming wave. [8] Consequently, on the northern hemisphere, the amphidromic point will be displaced from the centre line of the channel towards the left of the direction of the incident wave.
A tidal wave can often be described as a sum of harmonic waves. The principal tide (1st harmonic) refers to the wave which is induced by a tidal force, for example the diurnal or semi-diurnal tide. The latter is often referred to as the tide and will be used throughout the remainder of this article as the principal tide.
The tidal forces due to the Moon and Sun generate very long waves which travel all around the ocean following the paths shown in co-tidal charts. The time when the crest of the wave reaches a port then gives the time of high water at the port.
The tidal wave, a Kelvin wave, enters the domain in the lower left corner and travels to the right with the coast on its right. The sea surface height (SSH, left panels of animation 1), the tidal elevation, is maximum at the coast and decreases towards the centre of the domain.
It depends on local time and travels westward with the Sun. It is an external mode of class 2 and has the eigenvalue of ε 1 −2 = −12.56. Its maximum pressure amplitude on the ground is about 60 Pa. [5] The largest solar semidiurnal wave is mode (2, 2) with maximum pressure amplitudes at the ground of 120 Pa. It is an internal class 1 wave.
The clock of 1667 at Fécamp Abbey shows the time of local high tide, and the present state of the sea by means of a disc with a quarter-circle aperture which rotates with the lunar phase, revealing a green background at the syzygies (at new moon and full moon), when the tidal range is most extreme ("spring tides"), and a black background at ...
At first- and third-quarter phases of the moon, lunar and solar tides are perpendicular, and the tidal range is at a minimum. The semi-diurnal tides go through one full cycle (a high and low tide) about once every 12 hours and one full cycle of maximum height (a spring and neap tide) about once every 14 days.