Geopotential height or geopotential altitude is a vertical coordinate referenced to

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

's mean

sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardise ...

, an adjustment to geometric

height Height is measure of vertical distance, either vertical extent (how "tall" something or someone is) or vertical position (how "high" a point is). For example, "The height of that building is 50 m" or "The height of an airplane in-flight is ab ...

(

altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...

above mean sea level) that accounts for the variation of

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

with

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...

and altitude. Thus, it can be considered a "gravity-adjusted height". It is the altitude all aircraft's barometric altimeters are calibrated to.

Definition

At an elevation of

h

, the

geopotential Geopotential is the potential of the Earth's gravity field. For convenience it is often defined as the ''negative'' of the potential energy per unit mass, so that the gravity vector is obtained as the gradient of this potential, without the negat ...

is defined as: :

\Phi(h) = \int_0^h g(\phi,z)\,dz\, ,

where

g(\phi,z)

is the acceleration due to gravity,

\phi

is latitude, and

z

is the geometric elevation. Thus geopotential is the

gravitational potential energy Gravitational energy or gravitational potential energy is the potential energy a massive object has in relation to another massive object due to gravity. It is the potential energy associated with the gravitational field, which is released (conver ...

per unit mass at that elevation. The geopotential height is: :

(h) = \frac\, ,

which normalizes the geopotential to

g_0

= 9.80665 m/s², the standard gravity at mean sea level.

Usage

Geophysical Geophysics () is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. The term ''geophysics'' some ...

sciences such as meteorology often prefer to express the horizontal

pressure gradient force In fluid mechanics, the pressure-gradient force is the force that results when there is a difference in pressure across a surface. In general, a pressure is a force per unit area, across a surface. A difference in pressure across a surface t ...

as the gradient of

along a constant-pressure surface, because then it has the properties of a

conservative force In physics, a conservative force is a force with the property that the total work done in moving a particle between two points is independent of the path taken. Equivalently, if a particle travels in a closed loop, the total work done (the sum ...

. For example, the

primitive equations The primitive equations are a set of nonlinear partial differential equations that are used to approximate global atmospheric flow and are used in most atmospheric models. They consist of three main sets of balance equations: # A '' continuity e ...

which weather forecast models solve use

hydrostatic pressure Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body " fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an imm ...

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 ( highs and lows) which are typically seen on upper air charts. The geopotential thickness between pressure levels – difference of the 850

hPa HPA may refer to: Organizations * Harry Potter Alliance, a charity * Halifax Port Authority, Canada * Hamburg Port Authority, Germany * Hawaii Preparatory Academy, a school in Hawaii, US * Health Protection Agency, UK * Heerespersonalamt, the Ger ...

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. The

National Weather Service The National Weather Service (NWS) is an agency of the United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weather-related products to organizations and the public for the ...

defines geopotential height as:

References

External links

*{{Commonscatinline Atmospheric dynamics Vertical position fr:Hauteur du géopotentiel

Definition

Usage

See also

References

Further reading

External links