Mixed Tide

A mixed tide is a tidal regime carrying both diurnal and semidiurnal energy, so successive highs and lows differ markedly in height across the day, producing a pronounced diurnal inequality. It is identified by a form number F, the ratio (K1 plus O1) over (M2 plus S2), between 0.25 and 3.0; mixed-mainly-semidiurnal sits near the low end and mixed-mainly-diurnal near the high end. Much of the Pacific coast of North America is mixed: two highs and two lows per lunar day with a higher high water, a lower high water, a higher low water, and a lower low water, the basis of the MHHW and MLLW tidal datums.