The rise and fall of the sea water due to gravitational attraction of the Sun and Moon are called tides.
The Moon has about twice the tide-generating effect than the Sun because it is much closer to the Earth. Small horizontal forces tend to push water into two bulges on opposite sides of the Earth, one directly facing the tide-generating body and the other directly opposite.
Since the tidal bulges due to the Moon’s gravity are dominant, the tides observed on the Earth have periods dominated by lunar motions. They are modified by the changing position of the solar bulges.
The basic types of tides observed on the Earth are a diurnal tide (period of 1 lunar day), a semidiurnal tide (period of half a lunar day, like that predicted for the equilibrium tide), and a mixed tide, with characteristics of both.
Mixed tides are usually dominated by semidiurnal periods and display significant inequality. The inequalities are greatest when the Moon is over the tropics and least when it is over the Equator.