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5.1 Tides and Tidal Forcing

One of the worked examples of this case study is a model for barotropic tides, which are introduced at this point and will be discussed in more detail later on. The tidal model is simply the barotropic part of the sigma-coordinate 3-D model. Fortran 77 codes for scalar (Unix workstation), vector (Cray YMP) and massively parallel (Connection Machine) machines and a series of exercises are provided. It is therefore appropriate to discuss tides and tidal forcing before dealing with details of the sigma-coordinate model.

Gravitational attraction of the sun and the moon are responsible for the tidal motions on the globe, in all three media, the atmosphere, the oceans and the solid Earth. We will not go into great detail regarding this topic and the interested readers are referred to excellent books on the topic (for example Chapter 13 of Pond and Pickard [54], Chapter 11 of Dietrich et al. [11]). However, we will give enough information here so that the student can appreciate the nature of tidal processes around the globe.

The rhythmic rise and fall of sea level along the world's coastlines are the most apparent manifestation of tides in the global oceans. In some coastal locations, tides are noticeable but not spectacular, but in other places like the West coast of Korea and the Bay of Fundy, the tides are spectacularly large. In some places, the sea level rises and falls with a period of about half a day (these are called semi-diurnal tides), whereas in other places the period is more like a day (called diurnal tides). Yet again, in some locations the tides are mixed. And there are periods during the year, when the sun and moon line up with the Earth when the tides are unusually large.