Q1

Q1 is the larger lunar elliptic diurnal tidal constituent, period 26.8684 hours and speed 13.3987 degrees per hour, the diurnal-band counterpart of the semidiurnal N2. It accounts for the effect of the Moon’s orbital eccentricity on the diurnal declinational tide, modulating the O1 and K1 diurnal forcing over the anomalistic month. Q1 amplitude is typically a fifth to a sixth of O1, so it is a minor but standard member of the diurnal constituent set used in harmonic prediction. In strongly diurnal and mixed regimes, including Q1 improves the modeled day-to-day variation of the single daily high and low water.