Editing Gravity wave (section)

{{for|the phenomenon of general relativity |Gravitational wave}}
{{short description|Wave where gravity is the main restoring force}}
[[Image:Waves.jpg|thumb|right|Surface gravity wave, breaking on an ocean beach in [[Tučepi]], Croatia]]
[[Image:wave clouds.jpg|thumb|right|Wave clouds over [[Theresa, Wisconsin]], United States]]

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| title  = Nonfree image: detailed animation of a water wave
| image1 = [https://www.acs.psu.edu/drussell/Demos/waves/Water-2016.gif Detailed animation of water wave motion (CC-BY-NC-ND 4.0)]
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[[File:Satellite view of the Timor Sea (cropped).jpg|alt=wave clouds observed over the ocean, seen from a satellite|thumb|Wind-driven gravity waves in the [[Timor Sea]], Western Australia, as seen from space]]
In [[fluid dynamics]], '''gravity waves''' are waves in a [[fluid]] medium or at the [[interface (matter)|interface]] between two media when the [[force]] of [[gravity]] or [[buoyancy]] tries to restore equilibrium. An example of such an interface is that between the [[atmosphere]] and the [[ocean]], which gives rise to [[wind wave]]s.

A gravity wave results when fluid is displaced from a position of [[mechanical equilibrium|equilibrium]]. The restoration of the fluid to equilibrium will produce a movement of the fluid back and forth, called a '''''wave orbit'''''.<ref>{{Citation | publisher = Cambridge University Press | isbn = 978-0-521-01045-0 | last = Lighthill | first = James |author-link = James Lighthill | title = Waves in fluids | year = 2001 | page = 205 }}</ref> Gravity waves on an air–sea interface of the ocean are called '''surface gravity waves''' (a type of [[surface wave]]), while gravity waves that are {{em|within}} the body of the water (such as between parts of different densities) are called ''[[internal wave]]s''. [[Wind wave|Wind-generated waves]] on the water surface are examples of gravity waves, as are [[tsunami]]s, ocean [[tide]]s, and the [[Wake (physics)|wakes]] of surface vessels.

The period of wind-generated gravity waves on the [[free surface]] of the Earth's ponds, lakes, seas and oceans are predominantly between 0.3 and 30 seconds (corresponding to frequencies between 3&nbsp;Hz and .03&nbsp;Hz). Shorter waves are also affected by [[surface tension]] and are called ''[[gravity–capillary wave]]s'' and (if hardly influenced by gravity) ''[[capillary wave]]s''. Alternatively, so-called ''[[infragravity wave]]s'', which are due to [[undertone series|subharmonic]] [[nonlinear system|nonlinear]] wave interaction with the wind waves, have periods longer than the accompanying wind-generated waves.<ref>{{Citation
  | last1 = Bromirski
  | first1 = Peter D.
  | first2 = Olga V. 
  | last2 = Sergienko 
  | first3 = Douglas R. 
  | last3 = MacAyeal
  | title = Transoceanic infragravity waves impacting Antarctic ice shelves
  | journal = Geophysical Research Letters
  | volume = 37
  | issue = L02502
  | year = 2010
  | pages = n/a
 | doi = 10.1029/2009GL041488
  | postscript = .
| bibcode=2010GeoRL..37.2502B| s2cid = 38071443
 | url = https://escholarship.org/uc/item/3k2933rc
 | doi-access = free
  }}</ref>