A single periodic component of the tide, with a speed set by a combination of lunar and solar motions and a local amplitude and phase found by analysis. The tide at a station is predicted by adding dozens of constituents together; US predictions commonly use 37. Constituents carry short names such as M2, S2, K1 and O1, where the number indicates roughly how many cycles occur per day.
We only have a month of data, so we can resolve the big harmonic constituents but not split S2 from K2.
The number in a constituent's name gives its rough cycles per day, so names ending in 2 are semidiurnal and names ending in 1 are diurnal.
Also heard as
- tidal constituent
- constituent
Related terms
M2
The principal lunar semidiurnal constituent, period 12.42 hours, usually the largest part of the tide.
S2
The principal solar semidiurnal constituent, period exactly 12 hours, which beats with M2 to make springs and neaps.
K1
The lunisolar diurnal constituent, period about 23.93 hours, a main driver of once-daily tides.
O1
The principal lunar diurnal constituent, period about 25.82 hours, created by the Moon's declination.
Harmonic analysis
Breaking an observed water level or current record into its tidal constituents to find each one's amplitude and phase.