Gravity waves are waves in a fluid that obtain their restoring force from their buoyancy relative to the surrounding fluid.  See [0] for the gory details.<p>Some examples of gravity waves in the atmosphere: [1] [2]<p>[0] <a href="http:&#x2F;&#x2F;glossary.ametsoc.org&#x2F;wiki&#x2F;Gravity_wave" rel="nofollow">http:&#x2F;&#x2F;glossary.ametsoc.org&#x2F;wiki&#x2F;Gravity_wave</a>
[1] <a href="http:&#x2F;&#x2F;cimss.ssec.wisc.edu&#x2F;goes&#x2F;blog&#x2F;archives&#x2F;2051" rel="nofollow">http:&#x2F;&#x2F;cimss.ssec.wisc.edu&#x2F;goes&#x2F;blog&#x2F;archives&#x2F;2051</a>
[2] <a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=yXnkzeCU3bE" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=yXnkzeCU3bE</a>