Describe the tides in an open-ocean basin

Question

What will be an ideal response?

Answer 1

Idealized tidal bulges are freely propagating waves with the crests of the waves separated by a distance of one-half Earth's circumference—about 20,000 kilometers (12,420 miles). However, the tidal bulges themselves are continually pulled on by astronomical forces, so they actually exist on Earth as forced waves. What this means is they are continuously pulled along by a driving force, which is the tidal force caused mostly by the Moon. As a result, the tidal bulges move across Earth's oceans at about 1600 kilometers per hour to keep up with the tidal force of the Moon. It's the tidal bulge waveform—not the water itself—that moves at such great speeds.

A variety of conditions on the real Earth cause ocean tides to break up into distinct, large circulation units in each ocean basin called cells. In the open ocean, the crests and troughs of the tide wave rotate around an amphidromic point near the center of each cell. There is essentially no tidal range at amphidromic points, but radiating from each point are cotidal lines, which connect all nearby locations where high tide occurs simultaneously. The tide wave generally rotates counter- clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The wave must complete one rotation during the tidal period (usually 12 lunar hours), so this limits the size of the cells.