Editing Internal wave (section)

{{Short description|Type of wave within a fluid medium}}
[[Image:InternalWaves Gibraltar ISS009-E-09952 54.jpg|thumb|250px|'''Internal waves''' (marked with arrows), caused by tidal flow through the [[Strait of Gibraltar]] and made visible by sea surface roughness enhance sunlight backscatter]]
'''Internal waves''' are [[gravity wave]]s that [[oscillation|oscillate]] within a fluid medium, rather than on its surface. To exist, the fluid must be [[stratification (water)|stratified]]: the density must change (continuously or discontinuously) with depth/height due to changes, for example, in temperature and/or salinity. If the density changes over a small vertical distance (as in the case of the [[thermocline]] in lakes and oceans or an [[atmospheric inversion]]), the waves propagate horizontally like surface waves, but do so at slower speeds as determined by the density difference of the fluid below and above the interface. If the density changes continuously, the waves can propagate vertically as well as horizontally through the fluid.

Internal waves, also called internal gravity waves, go by many other names depending upon the fluid stratification, generation mechanism, amplitude, and influence of external forces. If propagating horizontally along an interface where the density rapidly decreases with height, they are specifically called interfacial (internal) waves. If the interfacial waves are large amplitude they are called internal solitary waves or internal [[soliton]]s. If moving vertically through the atmosphere where substantial changes in air density influences their dynamics, they are called anelastic (internal) waves. If generated by flow over topography, they are called [[Lee waves]] or [[mountain waves]]. If the mountain waves break aloft, they can result in strong warm winds at the ground known as [[Chinook winds]] (in North America) or [[Foehn]] winds (in Europe). If generated in the ocean by tidal flow over submarine ridges or the continental shelf, they are called internal tides. If they evolve slowly compared to the Earth's rotational frequency so that their dynamics are influenced by the [[Coriolis effect]], they are called [[inertia gravity waves]] or, simply, [[inertial waves]]. Internal waves are usually distinguished from [[Rossby wave]]s, which are influenced by the change of [[Coriolis frequency]] with latitude.