Tidal harmonic constituents

The tide at a place is represented as the sum of harmonic constituents, each a cosine term with its own amplitude and phase derived from a specific astronomical forcing. The principal lunar semidiurnal M2 dominates most open coasts, with S2 (principal solar semidiurnal), N2, K1, and O1 the next largest. Harmonic analysis of a tide-gauge record recovers the local amplitude and phase of each constituent, and tide prediction then sums them forward to give the height at any future time, the basis of every tide table and tidal stream atlas.