Goff-Gratch equation

	Email		Print
	Bookmark		Link

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. It is thought that the equation is applicable for temperatures below 0degC to approximately 100degC below zero. All such equations remain approximations, however.

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

Arden Buck Equation

The Arden Buck Equations are a group of equations which relate the saturation vapor pressure to temperature for moist air. The equations are more accurate than the Goff-Gratch equation in the range of -80 to 50?C....

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).

Discussion

Ask a question about 'Goff-Gratch equation'

Start a new discussion about 'Goff-Gratch equation'

Answer questions from other users

Full Discussion Forum

Encyclopedia

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

World Meteorological Organization

The World Meteorological Organization is an intergovernmental organization with a membership of 188 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873....
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

Pascal (unit)

The pascal is the SI derived unit of pressure, stress , Young's modulus and tensile strength. It is a measure of force per unit area i.e. equivalent to one newton per square meter or one joule per cubic meter....
)

T is the absolute air temperature in kelvin

Kelvin

The kelvin is a Units of measurement of temperature and is one of the seven SI base units. The Kelvin scale is a Thermodynamic temperature scale where absolute zero, the theoretical absence of all thermal energy, is zero ....
s

T_st is the steam-point (i.e. boiling point

Boiling point

The boiling point of a liquid is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....
at 1 atm.) temperature (373.15 K)

e^*_st is e^* at the steam-point pressure (1 atm = 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 (triple point

Triple point

In thermodynamics, the triple point of a substance is the temperature and pressure at which three Phase of that substance coexist in thermodynamic equilibrium....
) temperature (273.16 K)

e^*_i0 is e^* at the ice-point pressure (6.1173 hPa)

Goff-Gratch equation

Historical note

Equations

External links