Geopotential height

Geopotential height or geopotential altitude is a vertical coordinate referenced to Earth's mean sea level (assumed zero geopotential) that represents the work involved in lifting one unit of mass over one unit of length through a hypothetical space in which the acceleration of gravity is assumed constant.[1] In SI units, a geopotential height difference of one meter implies the vertical transport of a parcel of one kilogram; adopting the standard gravity value (9.80665 m/s2), it corresponds to a constant work or potential energy difference of 9.80665 joules.

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 amount of work is to be performed".[2] It is a useful concept in meteorology, climatology, and oceanography; it also remains a historical convention in aeronautics as the altitude used for calibration of aircraft barometric altimeters.[3]

  1. ^ Minzner, R. A.; Reber, C. A.; Jacchia, L. G.; Huang, F. T.; Cole, A. E.; Kantor, A. J.; Keneshea, T. J.; Zimmerman, S. P.; Forbes, J. M. (May 1976). "NASA Technical Report R-459: Defining Constants, Equations, and Abbreviated Tables of the 1976 Standard Atmosphere" (PDF). Archived from the original (PDF) on 2017-03-07.
  2. ^ Bjerknes, V. (1910). Dynamic Meteorology and Hydrography: Part [1]-2, [and atlas of plates]. Carnegie Institution of Washington publication. Carnegie Institution of Washington. p. 13. Retrieved 2023-10-05.
  3. ^ Anderson, John (2007). Introduction to Flight. McGraw-Hill Science/Engineering/Math. p. 109.