Regular changes in tidal heights are related to the lunar cycle and the seasons.
In my article about the Sea Shore I have deliberately avoided any discussion of tidal mechanisms. Most people are happy to accept that the sea recedes from the shore and then returns roughly twice a day, and many more are satisfied with an explanation that says ‘it is something to do with the effects of the gravity of the sun and moon on the water’.
As I understand it the sun and moon exert forces on the earth which result in distortions of the earth’s crust and oceans above it. Because the water is contained in discrete basins surrounded by the continents this water ‘sloshes about’, rising and falling in the centre and going ‘in and out’ at the edges. The precise shapes of channels etc. affects the timing of tides, which normally occur twice a day. ‘Tide Tables’ will allow you to predict the times and heights of the water at any coastal location you want to visit.
When you add in the fact that the lunar cycle (about 28 days) has a fortnightly effect on the tides (causing bigger ‘spring tides’ and smaller ‘neap tides’), and that there is also a seasonal effect causing twice yearly extremes – I have enough information as a Marine Biologist. Oceanographers probably want a bit more by way of explanation and detailed modelling, and if you think you fall into their category I offer links to a comprehensible explanation, a more complicated one, and one which few people will even be able to read out loud!.
It is a worrying fact that most elementary textbooks – in an attempt to keep explanations understandable maybe – give erroneous information and propose models that are just ‘plain wrong’.
