Many terms are used for describing the ocean circulation. Here are a few of the more commonly used terms for describing currents and waves.
1. General Circulation is the permanent, time-averaged circulation.
2. Abyssal also called the Deep Circulation is the circulation of mass, in the meridional plane, in the deep ocean, driven by mixing.
3. Wind-Driven Circulation is the circulation in the upper kilometer of the ocean forced by the wind. The circulation can be caused by local winds or by winds in other regions.
4. Gyres are wind-driven cyclonic or anticyclonic currents with dimensions nearly that of ocean basins.
5. Boundary Currents are currents flowing parallel to coasts. Two types of boundary currents are important:
- Western boundary currents on the western edge of the ocean tend to be fast, narrow jets such as the Gulf Stream and Kuroshio.
- Eastern boundary currents are weak, e.g. the California Current.
6. Squirts or Jets are long narrow currents, with dimensions of a few hundred kilometers, that are nearly perpendicular to west coasts.
7. Mesoscale Eddies are turbulent or spinning flows on scales of a few hundred kilometers.
In addition to flow due to currents, there are many types of oscillatory flows due to waves. Normally, when we think of waves in the ocean, we visualize waves breaking on the beach or the surface waves influencing ships at sea. But many other types of waves occur in the ocean.
1. Planetary Waves depend on the rotation of the earth for a restoring force, and they including Rossby, Kelvin, Equatorial, and Yanai waves.
2. Surface Waves sometimes called gravity waves, are the waves that eventually break on the beach. The restoring force is due to the large density contrast between air and water at the sea surface.
3. Internal Waves are subsea wave similar in some respects to surface waves. The restoring force is due to change in density with depth.
4. Tsunamis are surface waves with periods near 15 minutes generated by earthquakes.
5. Tidal Currents are horizontal currents and currents associated with internal waves driven by the tidal potential.
6. Edge Waves are surface waves with periods of a few minutes confined to shallow regions near shore. The amplitude of the waves drops off exponentially with distance from shore.
Robert H. Stewart
Department of Oceanography
Texas A & M University
September 2006 Edition