View source for Physics:Equivalent temperature

In [[Physics:Atmospheric science|atmospheric science]], '''equivalent temperature''' is the temperature of air in a parcel from which all the [[Physics:Water vapor|water vapor]] has been extracted by an [[Physics:Adiabatic|adiabatic]] process. 

Air contains water vapor that has been evaporated into it from liquid sources (lakes, sea, etc...). The energy needed to do that has been taken from the air. Taking a volume of air at [[Physics:Temperature|temperature]] T and [[Chemistry:Mixing ratio|mixing ratio]] of  r&nbsp;, drying it by condensation will restore energy to the airmass. This will depend on the [[Physics:Latent heat|latent heat]] release as: 

:<math>T_e \approx T + \frac {L_v}{c_{pd}}r</math>

where:

* <math>\,L_v</math> : [[Physics:Latent heat|latent heat]] of [[Physics:Evaporation|evaporation]] (2400 kJ/kg {at 25C} to 2600 kJ/kg {at -40C})
* <math>\,c_{pd}</math> : [[Physics:Specific heat|specific heat]] at constant pressure for air (<math>\approx</math> 1004 J/(kg·K)) 

Tables exist for exact values of the last two coefficients.

== See also ==
* [[Physics:Wet-bulb temperature|Wet-bulb temperature]]
* [[Earth:Potential temperature|Potential temperature]]
* [[Earth:Atmospheric thermodynamics|Atmospheric thermodynamics]]
* [[Physics:Equivalent potential temperature|Equivalent potential temperature]]

==Bibliography==
* M Robitzsch, ''Aequivalenttemperatur und Aequivalentthemometer'', Meteorologische Zeitschrift, 1928, pp. 313-315.
* M K Yau and R.R. Rogers, ''Short Course in Cloud Physics, Third Edition'', published by Butterworth-Heinemann, January 1, 1989, 304 pages. {{ISBN|9780750632157}} {{ISBN|0-7506-3215-1}}
* J.V. Iribarne and W.L. Godson, ''Atmospheric Thermodynamics'', published by D. Reidel Publishing Company, Dordrecht, Holland, 1973, 222 pages

{{Meteorological variables}}


[[Category:Atmospheric thermodynamics]]

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