4 - Tidal Constituents and the Harmonic Method

Summary

Based on the overview from the previous chapter, the main tidal constituents are understood intuitively when their frequencies are derived. This involves the three species of long-period, diurnal, and semidiurnal tides. The corrections needed for the lunar nodal cycle are discussed. The effect of the main constituents on the tidal signal are illustrated (modulation due to elliptic orbit, diurnal inequality, spring-neap, and related cycles). The principle of the method of harmonic analysis is explained. For the tidal signal as a whole, the notion of the tidal period is discussed, including its variability and long-term mean, as well as the presence of circa-tidal clocks in marine organisms.