Oceanography

a. Standing waves

Deep-water waves, shallow-water waves, and internal waves are all progressive waves; they have a speed and move in direction. Standing waves do not progress; they are reflected back on themselves and appears as an alternation between a trough and a crest at a fixed position. They occur in ocean basins, partly enclosed bays, and estuaries. A standing wave can be demonstrated by slowly lifting one end of a container partially filled with water and then rapidly but gently returning it to a level position. If this is done, the surface alternately rises at one end and falls at the other end of the container. The surface oscillates about a point at the center of the container is the node, and the alternations of low and high water at each end are antinodes. A standing wave is a progressive wave reflected back on itself; the reflection cancels out the forward motions of the initial and reflected waves.

Standing waves in bays or inlets with an open end behave somewhat differently than standing waves in closed basins. A node is usually located at the entrance to the open-ended bay, so only one-quarter of the wavelength is inside the bay. There is little or no rise and fall of the water surface at the entrance, but a large rise and fall occurs at the closed end of the bay. Multiple nodes may also be present in open-ended basins.