Equilibrium Theory of Tides

Tidal Forces

Equilibrium theory makes the following assumptions:

  • Tidal-potential can be determined from celestial mechanics

  • Oceans of uniform depth cover the earth

  • The earth is not rotating, so no Coriolis force acts

  • No friction acts

Given these assumptions, equilibrium theory predicts a maximum tidal range of 0.5 - 1 m.

Dynamic theory takes the earth's true nature into account:

  • Earth is rotating

  • Continents exist

  • Bathymetry is highly irregular

  • Friction acts

  • Tides are long waves (highest frequency harmonics are semi-diurnal) so they behave as shallow-water waves

The dynamic theory doesn't perfectly predict tides either, but it provides a much better explanation for observed tidal patterns. The most accurate method of tidal predication (near coasts, at least) is to carefully measure tides over an extended period, and use harmonic analysis.

Tidal Components
Equilibrium Theory
Dynamic Theory
Amphidromic Systems
Tide Waves
Closed Basins & Channels
Arctic & Antarctic Tides


Author: E. Boyce
Created: 7 December, 2003
Web project for PHYS645 Fundamentals of Geophysical Fluid Dynamics, University of Alaska Fairbanks