5.4 DYNAMIC THEORY

Question 1

Why is equilibrium theory incorrect?

Answer 1

1. The presence of land prevents tidal bulges from directly circumnavigating the globe.
2. Rotation of the earth on its axis is too rapid for inertia of the water masses to overcome in sufficient time to establish an immediate equilibrium tide (ocean depth = 20km). The wavelength of tides is long compared to ocean depth, so they travel as shallow water waves (speed = root gh).
3. Water movements induced by tide generating forces are subject to coriolis and friction forces, which deflect tidal flows to the right in the northern hemisphere and left in the southern hemisphere.

Question 2

What are the 4 main things resulting in the observed tide being different from the equilibrium?

Answer 2

1. Amphidromic systems
2. Standing waves - resonance
3. Shallow water waves
4. Topography