Oceanography

3.1.4.Tides and Tidal ranges

As the earth revolves on its axis coastal areas periodically pass through the tidal bulges and experience high and low tides. As the crest of a bulge passes, high tide occurs. Troughs between bulges result in low tides. Tidal range is the difference in height between high and low tides. A continuous record of the daily change in sea level because of tides is a tidal curve.

Tidal curves show that tides change daily in range and time of occurrence. The variation results from the complex interaction of the earth sun and moon. The interaction of these there bodies is so complex that a given coast may experience the same tidal conditions only once each 1600 years.

Solar tides: Is the tides produced by the Sun which occur approximately at the same time each day because the earth rotates on its axis once each 24 hours. Coastal areas experience a solar high or low tide each 12 hours. Lunar tides are more complex because the Moon moves forward in its orbit as the earth rotates on its axis. Thus, a point on the earth directly below the Moon requires 24 hours and 50 minutes before it is again below the Moon. Lunar tides occur 50 minutes later each day. Coastal areas experience a lunar tide each 12 hours and 25 minutes internel.