Internal wave
From Wikipedia, the free encyclopedia
Internal waves are gravity waves that oscillate due to the buoyancy force. The simplest example are the waves generated on the interface between two fluids of different densities. A good way to visualize internal waves of this sort is to observe the waves on an oil-water interface. Internal waves typically have much lower frequencies and higher amplitudes than surface waves. This is because the density differences within a fluid are typically much less than the density of the fluid itself.
The atmosphere and ocean are continuously stratified: potential density generally increases steadily downward. Internal waves in a continuously stratified medium may propagate vertically as well as horizontally. The dispersion relation for such waves is curious: the direction of propagation of energy (group velocity) is perpendicular to the direction of propagation of wave crests and troughs (phase velocity). Internal wave motions are ubiquitous in the ocean and atmosphere where they are influenced by the rotation of the earth as well as by the stratification of the medium. The frequencies of these geophysical wave motions vary from a lower limit of the Coriolis frequency (inertial motions) up to the Brunt-Väisälä, or buoyancy frequency (buoyancy oscillations). Internal waves at tidal frequencies are produced by tidal flow over topography/bathymetry, and are known as internal tides. Nonlinear solitary internal waves are called solitons.
[edit] External link
- Directions for making an oil and water wave toy.
- More discussion and videos of internal waves made by an oscillating cylinder:
