Parameter Tree:
EARTH SCIENCE > ATMOSPHERE > ATMOSPHERIC TEMPERATURE > SURFACE TEMPERATURE > VIRTUAL TEMPERATURE

Definition:
(Also called density temperature.) The virtual temperature Tv = T(1 + rv/ ?)/(1 + rv), where rv is the mixing ratio and ? is the ratio of the gas constants of air and water vapor, ? 0.622.

Reference:
Glossary of Meteorology, American Meteorological Society, 2013, http://glossary.ametsoc.org/wiki/Virtual_temperature