Saturation equivalent potential temperature

saturation equivalent potential temperature

Saturation equivalent potential temperature (represented as θ_es) is a special case of equivalent potential temperature (θ_e) computed by assuming an air parcel is saturated (i.e., r = r_sat in the equation for θ_e)and thus represents the theoretical maximum θ_e. Both θ_es and θ_e are themselves special cases of potential temperature (θ), accounting for the latent heat release due to condensation of water vapor by lifting the parcel to a new temperature and pressure via a pseudoadiabatic process prior to computing the potential temperature. Hence, θ_es is conserved for a reversible moist adiabatic process. The relationship between the three types of potential temperature can be described as follows, where r represents the parcel water vapor mixing ratio and r_sat is the saturation value of water vapor mixing ratio based on the parcel temperature and pressure:

r = r_sat (saturated environment): θ_e = θ_es,
r = 0 (dry environment): θ_e = θ, and
0 < r < r_sat (unsaturated moist parcel): θ < θ_e< θ_es.

Reference:

Bohren, C. F., and B. A. Albrecht, 1998: Atmospheric Thermodynamics. Oxford University Press, 293–294.

(term edited 8/22/2014)

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