Declinational Tide

A declinational tide is the part of the tide forced by the changing declination of the Moon or Sun, the angle of the perturbing body above or below the equatorial plane, which is captured by the declinational constituents K1, O1, and K2. When declination is large the two daily tidal bulges fall at different latitudes, so a given station sees two unequal highs, the source of the diurnal inequality, and the diurnal constituents reach maximum amplitude. At zero declination, near the lunar equator crossing, the diurnal forcing nearly vanishes and the tide becomes most strongly semidiurnal. This declinational cycle modulates tropic and equatorial tides over the 27.2-day tropical month.