Information about Goff Gratch Equation

The Goff-Gratch equation is one (arguably the first reliable) amongst many equations that have been proposed to estimate the saturation water vapor pressure at a given temperature. All such equations remain approximations, however.

Another similar equation based on more recent data is the Arden Buck Equation

Historical note

This equation is named after the authors of the original scientific article who described how to calculate the saturation water vapor pressure above a flat free water surface as a function of temperature (Goff and Gratch, 1946). Goff (1957) later revised his formula, and the latter was recommended for use by the World Meteorological Organization in 1988, with further corrections in 2000.

Equations

The original Goff-Gratch (1946) equation reads as follows:

where:

log refers to the logarithm in base 10

e^* is the saturation water vapor pressure (hPa)

T is the absolute air temperature in kelvins

T_st is the steam-point temperature (373.15 K)

e^*_st is e^* at the steam-point pressure(1013.25 hPa)

Similarly, the equation for the saturation water vapor pressure over ice is:

where:

log stands for the logarithm in base 10

e^*_i is the saturation water vapor pressure over ice (hPa)

T is the air temperature (K)

T₀ is the ice-point temperature (273.15 K)

e^*_i0 is e^* at the ice-point pressure (6.1071 hPa)

References

• Goff, J. A., and S. Gratch (1946) Low-pressure properties of water from -160 to 212 °F, in Transactions of the American Society of Heating and Ventilating Engineers, pp 95-122, presented at the 52nd annual meeting of the American Society of Heating and Ventilating Engineers, New York, 1946.
• Goff, J. A. (1957) Saturation pressure of water on the new Kelvin temperature scale, Transactions of the American Society of Heating and Ventilating Engineers, pp 347-354, presented at the semi-annual meeting of the American Society of Heating and Ventilating Engineers, Murray Bay, Que. Canada.
• World Meteorological Organization (1988) General meteorological standards and recommended practices, Appendix A, WMO Technical Regulations, WMO-No. 49.
• World Meteorological Organization (2000) General meteorological standards and recommended practices, Appendix A, WMO Technical Regulations, WMO-No. 49, corrigendum.

External links

• http://cires.colorado.edu/~voemel/vp.html

The saturation vapor pressure is the static pressure of a vapor when the vapor phase of some material is in equilibrium with the liquid phase of that same material. The saturation vapor pressure of any material is solely dependent on the temperature of that material.
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The Arden Buck Equation is an equation describing the saturation vapor pressure of water at various temperatures. It is based on more recent experiments than the Goff-Gratch equation.

A set of several equations were developed, each of which is applicable in a different situation.
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The World Meteorological Organization (WMO) is an intergovernmental organization with a membership of 188 Member States and Territories. It originated from the International Meteorological Organization (IMO), which was founded in 1873.
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The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Young's modulus and tensile strength). It is a measure of perpendicular force per unit area i.e. equivalent to one newton per square meter or one Joule per cubic meter.
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Thermodynamic temperature is the absolute measure of temperature and is one of the principal parameters of thermodynamics. Thermodynamic temperature is an “absolute” scale because it is the measure of the fundamental property underlying temperature: its null
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The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. The Kelvin scale is a thermodynamic (absolute) temperature scale where absolute zero — the coldest possible temperature — is zero kelvins
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