K2

K2 is the luni-solar declinational semidiurnal tidal constituent, period 11.9672 hours and speed 30.0821 degrees per hour, slightly faster than the principal solar S2. Like K1 it merges lunar and solar declinational effects into one term, and it modulates the semidiurnal tide together with S2 over the declinational cycle. K2 enhances the spring tide near the equinoxes when declination is small and the solar tide aligns most directly with the lunar. Its amplitude is roughly a quarter of S2, so harmonic analysis must resolve K2 and S2 separately, which needs a record long enough to separate their close frequencies, about six months at minimum.