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Potential Temperature

Derived directly from integration of the 1st law of thermodynamics. It is the temperature a parcel of air at P and T would have if it were at Ps. It is conserved for adiabatic motions, ( i.e., dTheta/dt = 0).

dQ/(n · <mw> · T) = (Cp dT/T) - (Rg dP/P) = 0
Theta = T · (Ps/P)kappa = P/(rho Rg) [(Ps/P)kappa]     kappa = Rg/Cp

For earth kappa = 0.286 (<mw> = 28.96, Cp = 1.004 Joules/gram/K). Some authors write this equation with gamma = Cp/Cv = 1/(1-kappa)

partial P/partial z = - rho · g = (P · g)/(Rg · T) = - P/H(z)
partial log(P) = -H(z) · partial z
therefore,
P/Ps = e- integdz'/H(z')
Theta = T · e- integdz'/H(z')
if H(z) = H0
Theta = T · e-kappa · z/H0