Equivalent potential temperature
From AMS Glossary
equivalent potential temperature
(Also called wet-equivalent potential temperature.) A thermodynamic quantity, with its natural logarithm proportional to the entropy of moist air, that is conserved in a reversible moist adiabatic process.
It is given most accurately as
where θe is the equivalent potential temperature, cpd is the heat capacity at constant pressure of dry air, rt is the total water mixing ratio, c is the heat capacity of liquid water, T is the temperature, Rd is the gas constant for dry air, pd is the partial pressure of dry air, p0 is a reference pressure (usually 100 kPa), Lv is the latent heat of vaporization, rv is the vapor mixing ratio, Rv is the gas constant for water vapor, and Η is the relative humidity. Neglect of the quantity rtc, where it appears, yields a simpler expression with good accuracy.
Paluch, I. 1979. J. Atmos. Sci.. 36. 2467–2478.
Emanuel, K. A. 1994. Atmospheric Convection. Oxford University Press, . 580 pp.