What influences tide-height the most? Can I guess the height by looking on a globe?

Question

I hope that the question title is resonably clear: What are the most significant factors which influence the tide height? I'm aware of the following couple of them:

• Sun-Earth-Moon relative position (higher tide when co-linear)
• Size of the land/peninsula/island (higher for larger lands I suppose?)
• Shape of the surrounding seafloor (Hawaii has low tide partly because it has no shelf)

However, I'm really curious as which are the most important amongst them? Or is it even possible to guess the tide height if I know the Lunar phase and I have a good globe with sea depth?

Answer 1

I don't know about the size of land masses, but their distribution and the shape of ocean basins definitely play a big role. When considering the ideal case of an all-ocean globe, i.e. one with no land masses (equilibrium tidal theory), the combined effect of sun and moon give a theoretical tidal range of less than 1 m⁽¹⁾. As tidal ranges can be much larger than this, there are other effects that has a greater influence.

The Bay of Fundy for example, is one of the places with the largest difference between low tide and high tide, at about 16 m. The large difference in this location has to do with the shape of the bay. The bay has a natural frequency for waves that is about the same as the frequency of the tide itself, giving an amplification of the tidal amplitude. In addition there is a funnelling effect in the inner part of the bay, giving an additional contribution.⁽²⁾

Another example of large tidal differences is the English channel, particularly the French side. In this case the tides are large at least partly because the tide moves as a coastal trapped Kelvin wave. These are waves that propagate along land, with the land to the right when looking in the direction of propagation (on the Northern hemisphere, land to the right on SH). The amplitude of the wave is highest near the coast, decaying exponentially away from the coast. As the tide in the English channel moves northward, the largest tidal range is on the French side.

With regard to guessing the tidal range, this is not entirely straight forward. First, when discussing tides, we generally split the tidal potential into a series of oscillations having different frequencies, mainly either diurnal (period of ~24 h) or semi-diurnal (period of ~12 h). These given frequencies are obtained through trigonometric considerations, and depend on the latitude of the point, the declination of the moon or sun relative to the equator, and the hour angle. (The hour angle is basically the longitudinal difference between the sub-lunar point and the point we consider.) Each of these components can vary in time and space.

Further, the pattern of the amplitudes of each component is not necessarily simple. In addition to the differences in potential, the topography modifies it. See for example:

^{from wikipedia}

which shows the amplitude of the M2 tidal component. This is the strongest semi-diurnal tidal component caused by the moon. You'll notice that there are places where the amplitude is zero, i.e. this component causes no tides here. These are known as amphidromic points.

Also, depending on which components dominate at a given location, you can have either a mainly semi-diurnal tide, a mainly diurnal tide, or a mixed tide where there are two high tides in a day, but one has lower amplitude than the other. A sketch of which can be seen here:

^{from wikipedia}

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⁽¹⁾ Pugh, David T. (1987) Tides, surges and mean sea level, chapter 3.

⁽²⁾ http://www.bayoffundy.com/about/highest-tides/ (for lack of better sources)