Tidal harmonic constituents

Summary

Tidal harmonic constituents are the sinusoidal terms into which the tide at a place is decomposed. Each has a frequency fixed by astronomy, from the rates of the Earth's rotation and of the orbits of the Moon and the Sun. Its amplitude and phase are fixed by the local response of the sea. Harmonic analysis of a tide gauge record estimates these amplitudes and phases, and summing the terms predicts future tides. The main ones are the lunar semidiurnal $M_2$, the solar semidiurnal $S_2$ and the diurnal $K_1$ and $O_1$.