Chapter 7 - Some Mathematics:
The Equations of Motion
7.3 Types of Flow in the Ocean
Many terms are used for describing the oceans circulation. Here are a few of the more commonly used terms for describing currents and waves.
- General Circulation is the permanent, time-averaged circulation.
called the Deep Circulation is the circulation
of mass in the deep ocean, driven by mixing.
- 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.
- Gyres are wind-driven cyclonic or anticyclonic
currents with dimensions nearly that of ocean basins.
- Boundary Currents are currents owing
parallel to coasts. Two types of boundary currents are important:
Squirts or Jets are long narrow currents, with dimensions of a few hundred kilometers, that are nearly perpendicular to west coasts.
Mesoscale Eddies are turbulent or spinning
flows on scales of a few hundred kilometers.
- Western boundary currents on the western edge of the oceans tend to be
fast, narrow jets such as the Gulf Stream and Kuroshio.
- Eastern boundary currents are weak, e.g. the
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.
- Planetary Waves depend on the rotation of the Earth for a restoring force,
and they including Rossby, Kelvin, Equatorial, and Yanai waves.
- 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.
- Internal Waves are subsea wave similar in
some respects to surface waves. The restoring force is due to change in density
- Tsunamis are surface waves with periods near 15 minutes generated by earthquakes.
- Tidal Currents are horizontal currents and
currents associated with internal waves driven by the tidal potential.
- Edge Waves are waves with periods of a
few minutes con ned to shallow regions near shore. The amplitude of the waves
drops off exponentially with distance from shore.