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Geopotential height is a vertical coordinate referenced to Earth's mean sea level — an adjustment to geometric height (elevation
Elevation

The elevation of a geographic location is its height above a fixed reference point, often the above mean sea level. Elevation, or geometric height, is mainly used when referring to points on the Earth's surface, while altitude or geopotential height is used for points above the surface, such as an aircraft in flight or a s...
 above mean sea level) using the variation of gravity with latitude
Latitude

Latitude, usually denoted symbolically by the Greek letter phi gives the location of a place on Earth north or south of the equator. Lines of Latitude are the horizontal lines shown running east-to-west on maps ....
 and elevation. Thus it can be considered a "gravity-adjusted height." One usually speaks of the geopotential height of a certain pressure level, which would correspond to the geopotential height necessary to reach the given pressure.

At an elevation of , the geopotential is defined as

where is the acceleration due to gravity, is latitude, and is the geometric elevation.

Thus, it is the gravitational potential energy per unit mass at that level.






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Geopotential height is a vertical coordinate referenced to Earth's mean sea level — an adjustment to geometric height (elevation
Elevation

The elevation of a geographic location is its height above a fixed reference point, often the above mean sea level. Elevation, or geometric height, is mainly used when referring to points on the Earth's surface, while altitude or geopotential height is used for points above the surface, such as an aircraft in flight or a s...
 above mean sea level) using the variation of gravity with latitude
Latitude

Latitude, usually denoted symbolically by the Greek letter phi gives the location of a place on Earth north or south of the equator. Lines of Latitude are the horizontal lines shown running east-to-west on maps ....
 and elevation. Thus it can be considered a "gravity-adjusted height." One usually speaks of the geopotential height of a certain pressure level, which would correspond to the geopotential height necessary to reach the given pressure.

At an elevation of , the geopotential is defined as

where is the acceleration due to gravity, is latitude, and is the geometric elevation.

Thus, it is the gravitational potential energy per unit mass at that level. The geopotential height is

where is the standard gravity at mean sea level.

Geophysical scientists often use geopotential height rather than geometric height, because doing so in many cases makes analytical calculations more convenient. For example, the primitive equations
Primitive equations

The primitive equations are a set of nonlinear differential equations that are used to approximate global atmosphere and are used in most Global climate models....
 which weather forecast models solve are more easily expressed in terms of geopotential than geometric height. Using the former eliminates centrifugal force and air density (which is very difficult to measure) in the equations.

A plot of geopotential height for a single pressure level shows the troughs and ridges, Highs and Lows, which are typically seen on upper air charts. The geopotential thickness between pressure levels — difference of the 850 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
Geostrophic wind

The geostrophic wind is the theoretical wind that would result from an exact balance between the Coriolis effect and the pressure gradient force....
, which is faster where the contours are more closely spaced and tangential to the geopotential height contours.

See also

  • Above mean sea level
    Above mean sea level

    The term above mean sea level refers to the elevation or altitude of any object, relative to the average sea level datum . AMSL is used extensively in radio by engineers to determine the coverage area a station will be able to reach....


Further reading

  • Hofmann-Wellenhof, B. and Moritz, H. Physical Geodesy, 2005. ISBN 3211235841
  • Eskinazi, S. Fluid Mechanics and Thermodynamics of our Environment, 1975. ISBN 0122425405


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