Editing Internal wave (section)

==Properties of internal waves==
{{Unreferenced section|date=November 2010}}
Internal waves typically have much lower frequencies and higher amplitudes than [[ocean surface wave|surface gravity waves]] because the density differences (and therefore the restoring forces) within a fluid are usually much smaller. Wavelengths vary from centimetres to kilometres with periods of seconds to hours respectively.

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: For a freely-propagating internal [[wave packet]], the direction of propagation of energy ([[group velocity]]) is perpendicular to the direction of propagation of wave crests and troughs ([[phase velocity]]). An internal wave may also become confined to a finite region of [[altitude]] or depth, as a result of varying stratification or [[wind]]. Here, the wave is said to be ''ducted'' or ''trapped'', and a vertically [[standing wave]] may form, where the vertical component of [[group velocity]] approaches zero. A ducted internal wave ''mode'' may [[Wave propagation|propagate]] horizontally, with parallel [[group velocity|group]] and [[phase velocity]] [[Vector (geometry)|vectors]], analogous to [[wave propagation|propagation]] within a [[waveguide]].

At large scales, internal waves are influenced both 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 waves|inertial motions]]) up to the [[Brunt–Väisälä frequency]], or buoyancy frequency (buoyancy oscillations). Above the [[Brunt–Väisälä frequency]], there may be [[Evanescent wave|evanescent]] internal wave motions, for example those resulting from partial [[reflection (physics)|reflection]]. Internal waves at tidal frequencies are produced by [[tide|tidal flow]] over topography/bathymetry, and are known as [[internal tides]]. Similarly, [[atmospheric tides]] arise from, for example, non-uniform solar heating associated with [[diurnal motion]].