Editing Coriolis force (section)

===Meteorology and oceanography===
[[File:Northern vs Southern hemisphere tropical cyclones.jpg|thumb|Due to the Coriolis force, low-pressure systems in the Northern hemisphere, like [[Typhoon Nanmadol (2022)|Typhoon Nanmadol]] (left), rotate counterclockwise, and in the Southern hemisphere, low-pressure systems like [[Cyclone Darian]] (right) rotate clockwise.]]
[[File:Coriolis effect10.svg|thumbnail|Schematic representation of flow around a '''low'''-pressure area in the Northern Hemisphere. The Rossby number is low, so the centrifugal force is virtually negligible. The pressure-gradient force is represented by blue arrows, the Coriolis acceleration (always perpendicular to the velocity) by red arrows]]
[[File:Coriolis effect14.png|thumb|Schematic representation of inertial circles of air masses in the absence of other forces, calculated for a wind speed of approximately {{convert|50|to|70|m/s|mph|sp=us|abbr=on}}.]]
[[File:The Earth seen from Apollo 17.jpg|right|thumbnail|Cloud formations in a famous image of Earth from Apollo 17, makes similar circulation directly visible]]

Perhaps the most important impact of the Coriolis effect is in the large-scale dynamics of the oceans and the atmosphere. In meteorology and [[oceanography]], it is convenient to postulate a rotating frame of reference wherein the Earth is stationary. In accommodation of that provisional postulation, the [[Centrifugal force|centrifugal]] and Coriolis forces are introduced. Their relative importance is determined by the applicable [[Coriolis effect#Length scales and the Rossby number|Rossby numbers]]. [[Tornado]]es have high Rossby numbers, so, while tornado-associated centrifugal forces are quite substantial, Coriolis forces associated with tornadoes are for practical purposes negligible.<ref name=Holton2>{{cite book| title=An Introduction to Dynamic Meteorology |year=2004 |author=Holton, James R.  |url=https://books.google.com/books?id=fhW5oDv3EPsC&pg=PA64|page=64 |isbn=9780123540157 |publisher=Elsevier Academic Press |location=Burlington, MA}}</ref>

Because surface ocean currents are driven by the movement of wind over the water's surface, the Coriolis force also affects the movement of ocean currents and [[hurricane|cyclones]] as well. Many of the ocean's largest currents circulate around warm, high-pressure areas called [[gyre]]s. Though the circulation is not as significant as that in the air, the deflection caused by the Coriolis effect is what creates the spiralling pattern in these gyres. The spiralling wind pattern helps the hurricane form. The stronger the force from the Coriolis effect, the faster the wind spins and picks up additional energy, increasing the strength of the hurricane.<ref name="Coriolis effect">{{cite web|last=Brinney|first=Amanda |title= What Is the Coriolis Effect? |url=https://www.thoughtco.com/what-is-the-coriolis-effect-1435315 | work=ThoughtCo.com}}</ref>{{better source needed|date = June 2023}}

Air within high-pressure systems rotates in a direction such that the Coriolis force is directed radially inwards, and nearly balanced by the outwardly radial pressure gradient. As a result, air travels clockwise around high pressure in the Northern Hemisphere and anticlockwise in the Southern Hemisphere. Air around low-pressure rotates in the opposite direction, so that the Coriolis force is directed radially outward and nearly balances an inwardly radial [[pressure gradient]].<ref>{{Cite news| url=https://www.nationalgeographic.org/encyclopedia/coriolis-effect/ |title=The Coriolis Effect: Earth's Rotation and Its Effect on Weather | format = grades 3-12 teaching resource | author = Evers, Jeannie (Ed.) | date=May 2, 2023| location = Washington, DC | publisher =National Geographic Society| access-date=2018-01-17|language=en}}</ref>{{better source needed|date = June 2023}}

====Flow around a low-pressure area====
{{Main|Low-pressure area}}
If a low-pressure area forms in the atmosphere, air tends to flow in towards it, but is deflected perpendicular to its velocity by the Coriolis force. A system of equilibrium can then establish itself creating circular movement, or a cyclonic flow. Because the Rossby number is low, the force balance is largely between the [[pressure-gradient force]] acting towards the low-pressure area and the Coriolis force acting away from the center of the low pressure.

Instead of flowing down the gradient, large scale motions in the atmosphere and ocean tend to occur perpendicular to the pressure gradient. This is known as [[geostrophic flow]].<ref name=Barry>{{cite book| title=Atmosphere, Weather and Climate |author = Barry, Roger Graham & Chorley, Richard J. | url=https://books.google.com/books?id=MUQOAAAAQAAJ&pg=PA115|page=115 |isbn=9780415271714 |year=2003 | location = Abingdon-on-Thames, Oxfordshire, England | publisher=Routledge-Taylor & Francis}}</ref> On a non-rotating planet, fluid would flow along the straightest possible line, quickly eliminating pressure gradients. The geostrophic balance is thus very different from the case of "inertial motions" (see below), which explains why mid-latitude cyclones are larger by an order of magnitude than inertial circle flow would be.{{citation needed|date = June 2023}}

This pattern of deflection, and the direction of movement, is called [[Buys-Ballot's law]]. In the atmosphere, the pattern of flow is called a [[cyclone]]. In the Northern Hemisphere the direction of movement around a low-pressure area is anticlockwise. In the Southern Hemisphere, the direction of movement is clockwise because the rotational dynamics is a mirror image there.<ref>{{cite web | last = Nelson | first = Stephen | title = Tropical Cyclones (Hurricanes) | work = Wind Systems: Low Pressure Centers | location = New Orleans, LA | publisher = [[Tulane University]] | date = Fall 2014 | url = http://www.tulane.edu/~sanelson/New_Orleans_and_Hurricanes/tropical_cyclones.htm | access-date = 2016-12-24 }}</ref> At high altitudes, outward-spreading air rotates in the opposite direction.{{citation needed|date = June 2023}}<ref>For instance, see the image appearing in this source: {{cite web | author = NASA Staff | date =  | title = Cloud Spirals and Outflow in Tropical Storm Katrina from Earth Observatory | work = JPL.NASA.gov | url = https://photojournal.jpl.nasa.gov/catalog/PIA04384 | access-date =  | location =  | publisher = [[NASA]]  }}{{full citation needed|date = June 2023}}</ref>{{full citation needed|date = June 2023}} Cyclones rarely form along the equator due to the weak Coriolis effect present in this region.<ref>{{Cite book| url=https://books.google.com/books?id=XRxzAwAAQBAJ&pg=PA326 |title=Encyclopedia of Disaster Relief |last1=Penuel|first1=K. Bradley |last2=Statler|first2=Matt |date=2010-12-29 |publisher=SAGE Publications |isbn=9781452266398 |page=326|language=en}}</ref>

====Inertial circles====
An air or water mass moving with speed <math>v\,</math> subject only to the Coriolis force travels in a circular trajectory called an ''inertial circle''. Since the force is directed at right angles to the motion of the particle, it moves with a constant speed around a circle whose radius <math>R</math> is given by:
<math display="block">R = \frac{v}{f}</math>
where <math>f</math> is the Coriolis parameter <math>2 \Omega \sin \varphi</math>, introduced above (where <math>\varphi</math> is the latitude). The time taken for the mass to complete a full circle is therefore <math>2\pi/f</math>. The Coriolis parameter typically has a mid-latitude value of about 10<sup>−4</sup>&nbsp;s<sup>−1</sup>; hence for a typical atmospheric speed of {{convert|10|m/s|mph|sp=us|abbr=on}}, the radius is {{convert|100|km|0|sp=us|abbr=on}} with a period of about 17&nbsp;hours. For an ocean current with a typical speed of {{convert|10|cm/s|mph|sp=us|abbr=on}}, the radius of an inertial circle is {{convert|1|km|1|sp=us|abbr=on}}. These inertial circles are clockwise in the northern hemisphere (where trajectories are bent to the right) and anticlockwise in the southern hemisphere.

If the rotating system is a parabolic turntable, then <math>f</math> is constant and the trajectories are exact circles. On a rotating planet, <math>f</math> varies with latitude and the paths of particles do not form exact circles. Since the parameter <math>f</math> varies as the sine of the latitude, the radius of the oscillations associated with a given speed are smallest at the poles (latitude of ±90°), and increase toward the equator.<ref name=Marshall2>{{Cite book|title= Atmosphere, Ocean and Climate Dynamics: An Introductory Text | page = 98 |author1=Marshall, John|author2=Plumb, R. Alan |url=https://books.google.com/books?id=aTGYbmVaA_gC&pg=PA98 |isbn=9780125586917 |year=2007 |publisher=Elsevier Academic Press |location=Amsterdam}}</ref>

====Other terrestrial effects====
The Coriolis effect strongly affects the large-scale oceanic and [[atmospheric circulation]], leading to the formation of robust features like [[jet stream]]s and [[western boundary current]]s. Such features are in [[geostrophic]] balance, meaning that the Coriolis and ''pressure gradient'' forces balance each other. Coriolis acceleration is also responsible for the propagation of many types of waves in the ocean and atmosphere, including [[Rossby wave]]s and [[Kelvin wave]]s. It is also instrumental in the so-called [[Ekman layer|Ekman dynamics]] in the ocean, and in the establishment of the large-scale ocean flow pattern called the [[Sverdrup balance]].