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Geopotential height differs from geometric height (as given by a tape measure) because Earth's gravity is not constant, varying markedly with altitude and latitude; thus, a 1-m geopotential height difference implies a different vertical distance in physical space: "the unit-mass must be lifted higher at the equator than at the pole, if the same ...
In geophysics and physical geodesy, a geopotential model is the theoretical analysis of measuring and calculating the effects of Earth's gravitational field (the geopotential). The Earth is not exactly spherical, mainly because of its rotation around the polar axis that makes its shape slightly oblate.
The equation that relates the two altitudes are (where z is the geometric altitude, h is the geopotential altitude, and r 0 = 6,356,766 m in this model): = Note that the Lapse Rates cited in the table are given as °C per kilometer of geopotential altitude, not geometric altitude.
The increase in altitude necessary for P or ρ to drop to 1/e of its initial value is called the scale height: H = R T M g 0 {\displaystyle H={\frac {RT}{Mg_{0}}}} where R is the ideal gas constant, T is temperature, M is average molecular weight, and g 0 is the gravitational acceleration at the planet's surface.
EGM96: The NASA GSFC and NIMA Joint Geopotential Model; Earth Gravitational Model 2008 (EGM2008) GeographicLib provides a utility GeoidEval (with source code) to evaluate the geoid height for the EGM84, EGM96, and EGM2008 Earth gravity models. Here is an online version of GeoidEval.
Since the atmosphere at a height of approximately 5.5 kilometres (3.4 mi) is mostly divergence-free, the barotropic model best approximates the state of the atmosphere at a geopotential height corresponding to that altitude, which corresponds to the atmosphere's 500 mb (15 inHg) pressure surface. [6]
Thus the standard consists of a tabulation of values at various altitudes, plus some formulas by which those values were derived. To allow modeling conditions below mean sea level , the troposphere is actually extended to −2,000 feet (−610 m), where the temperature is 66.1 °F (18.9 °C), pressure is 15.79 pounds per square inch (108,900 Pa ...
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 the geopotential, without the negation.