Tides in the North Sea as derived from observations. Red lines are co-phase lines of the M2 tide, labelled in hours after the moon's transit through the meridian of Greenwich. (There are thus only 25 minutes between the co-phase lines labelled 12 and 0.) Blue lines give the mean tidal range at spring tide (co-range lines of the sum of M2 and S2).

The progress of the tidal wave from the Atlantic Ocean into the North Sea is clearly demonstrated by the co-phase lines. The wave enters from the north and propagates along the British coast; it then proceeds around two amphidromic points along the Dutch, German and Danish coastline. Another wave enters from the south west, through the English Channel. In the Irish Sea the wave enters from the south.

The influence of the Coriolis force is demonstrated by the co-range lines, which show large tidal range along the British coast and small tidal range along the German, Danish and Norwegian coast. The same effect (amplification on the right side of the wave) is seen in the English Channel, where the tidal range along the French coast is as high as 11 m compared with 3 m on the English coast, and in the Irish Sea, where 8 m on the English coast compare with 2 m on the Irish coast.

© 1996 M. Tomczak

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