2.6.2 - Characteristics of the tide basins.

The tides do not have as a space unit the Earth, but several basins, each with its tidal wave, independent of the tide waves of the other basins.


© copyright notice ||| français ||| italiano

prologue > index tides > 2.6 - The mechanism of the tides.

2.6.1 The mechanism of the tides - introduction.
The tide basins.
The tide generation.
Water level variation.
Features of the tide waves.


Tidal basins.

A tidal wave does not develop itself around the Earth, from east to west, but within a tidal basin. There are several tidal basins; they may be small, medium, large, huge. The size of a tidal basin is related to water depth.

Inside each basin there is one tide wave, autonomous relative to the tides of other basins.

All the phases of the phenomenon take place within each basin: its generation (density decrease of the water), the transmission of the thrust fronts, their transformation unto tide wave components.

The tide basins as clock faces.

From high above a tide basin, one may see the tide wave move, clockwise if on the southern hemisphere; counter-clockwise, if on the northern one.

Fig. n° 1.

In the eastern basin of the North Atlantic, where tides occur twice a day, the cotidal lines (in red) show roughly the average delay given in hours of the first tide after the passage of the moon on the meridian, as well the average delay of the second tide, after the passage of the moon above the opposite meridian.

Where several basins get formed.

In the deep oceans, with large longitudinal extensions (Pacific, Indian), there are several huge tide basins.

Fig. n° 2.

courtesy NASA

Fig. n° 3.

In the North Sea, a shallow and relatively small sea, there are three little tide basins.

Fig. n° 4.

Tide waves and sublunar points.

On semi-diurnal basins, only on a limited section of each tide basin, the tide waves have a direct relation with the passage of the Moon above the meridian; the same occurs on the opposite tide basin.