Editing Geopotential height (section)

==Usage==
[[File:NAM 500 MB.PNG|thumb|upright=1.5|Geopotential height analysis on the [[North American Mesoscale Model]] (NAM) at 500 hPa.]]
[[Geophysics|Geophysical]] sciences such as meteorology often prefer to express the horizontal [[Pressure-gradient force|pressure gradient force]] as the gradient of [[geopotential]] along a constant-pressure surface, because then it has the properties of a [[conservative force]]. For example, the [[primitive equations]] that [[numerical weather prediction|weather forecast models]] solve use [[hydrostatic pressure]] as a vertical coordinate, and express the slopes of those pressure surfaces in terms of geopotential height. 

A plot of geopotential height for a single pressure level in the atmosphere shows the troughs and ridges ([[high-pressure area|highs]] and [[low-pressure area|lows]]) which are typically seen on upper air charts. The geopotential thickness between pressure levels – difference of the 850 [[Pascal (unit)|hPa]] and 1000 hPa geopotential heights for example – is proportional to mean [[virtual temperature]] in that layer. Geopotential height contours can be used to calculate the [[geostrophic wind]], which is faster where the contours are more closely spaced and tangential to the geopotential height contours.{{fact|date=February 2016}}

The United States [[National Weather Service]] defines geopotential height as:
{{Quotation|"...roughly the height above sea level of a pressure level. For example, if a station reports that the 500 mb [i.e. [[millibar]]] height at its location is 5600&nbsp;m, it means that the level of the atmosphere over that station at which the atmospheric pressure is 500&nbsp;mb is 5600 meters above sea level. This is an estimated height based on temperature and pressure data."<ref>{{cite web|title=Height|url=http://www.weather.gov/glossary/index.php?letter=h|work=NOAA's National Weather Service Glossary|publisher=NOAA National Weather Service|access-date=2012-03-15}}</ref>}}