Editing Secondary circulation (section)

{{short description|Circulation induced in a rotating system}}
{{One source|date=December 2019}}
In fluid dynamics, a '''secondary circulation''' or '''[[secondary flow]]''' is a weak circulation that plays a key maintenance role in sustaining a stronger '''primary circulation''' that contains most of the kinetic energy and momentum of a flow.<ref>{{Cite book|url=http://worldcat.org/oclc/1124306270|title=An introduction to dynamic meteorology.|last=Holton|first=James R.|date=2019 |publisher=Elsevier Science |isbn=9780128093290|oclc=1124306270}}</ref>  For example, a [[Tropical cyclone#Primary circulation: rotating winds|tropical cyclone's primary winds are tangential]] (horizontally swirling), but its [[Tropical cyclone#Physics and energetics|evolution and maintenance against friction]] involves an in-up-out secondary circulation flow that is also important to its clouds and rain. On a planetary scale, Earth's winds are mostly east–west or [[zonal and meridional|zonal]], but that flow is maintained against friction by the [[Coriolis force]] acting on a small north–south or [[meridional]] secondary circulation.