The unevenness between successive highs or successive lows in the same day, caused mainly by the declination of the Moon. In semidiurnal regions it is small; in mixed regions it is large enough that the tables list a higher high and a lower high, a higher low and a lower low. The inequality is greatest at tropic tides and least at equatorial tides.
Diurnal inequality is huge this week, the evening high is a metre over the morning one.
Also heard as
- daily inequality
- high water inequality
- low water inequality
Related terms
Mixed tide
A tide with two highs and two lows a day of clearly unequal heights, combining semidiurnal and diurnal parts.
Tropic tide
A tide occurring when the Moon is near its greatest declination, giving the largest daily inequality.
Declination
The angle of the Moon or Sun north or south of the celestial equator, which makes the two daily tides unequal.
Higher high water
The taller of a tidal day's two high waters, the one that matters most on mixed-tide coasts.