In oceanography or the study of the oceans, tides refer to the rise and fall of sea levels. A situation which is brought about by two things: the gravitational forces exerted by the sun and the moon and the rotation of the earth, which has 71% of its surface area as occupation zone for the ocean. However, in their cause of ocean tides, the moon to a greater extent, when compared with the Sun, influences tides due to its nearness to the earth on which the oceans lie.
The characteristics of tides vary in relation to the different types of tides available in the oceans of the world.
Diurnal tides
Diurnal tides occurs once in a day and any place or part of the ocean where diurnal tides are common or occur will normally experience one low tide and one high tide within a day or a 25 hours period.
Diurnal tides are usually characterized by rises and falls in water levels for prolonged periods of time and in some cases, a complete cease in ocean waves crashing on shores (when the single low tide is being experienced).
Semi-diurnal tides
Unlike diurnal tides, semi-diurnal tides occur two times in a day. They are also caused by the gravitational forces exerted by the sun and the moon (to a larger extent) and the movement of our planet, places or oceans where semi-diurnal tides occur usually go through two high tides and two low tides within 24 hours. The two high tides are, however, not similar in height, hence referred to as the higher high water (tide) and the lower high water.
The two low tides are also named higher low water and the lower low water.
Semi-diurnal tides, also, have as features rise and decline in water levelsand water rising to its highest level and flood tides.
Mixed tides
Mixed tides are said to be taking place when a single low tides occurs immediately after two high tides. Mixed tides, as the name suggests, have the characteristics that are common to both diurnal and semi-diurnal tides.
Places where mixed tides occur also experience ebb tides, water level falling and moving away from the shore, and flood tides, water level rising and covering a substantial chunk of the shoreline, over a period of time.
Web Sources:
Pictures of tides
http://www.universetoday.com/81898/tide
http:/dust.geo.orst.edu/oceans/tides.html
http:/en.wikipedia.org/wiki/Tide/Characteristics
