Equilibrium evaporation beneath a growing convective boundary layer

Expressions for the equilibrium surface Bowen ratio ( beta sub(s)) and equilibrium evaporation are derived for a growing convective boundary layer (CBL) in terms of the Bowen ratio at the top of the mixed layer ( beta sub(i)) and the entrainment parameter A sub(R). If A sub(R) is put equal to zero, the solution for beta sub(s) becomes that previously obtained for the zero entrainment or "closed box" model. The Priestley-Taylor parameter alpha is also calculated and plotted in terms of A sub(R) and beta sub(i). Realistic combinations of the atmospheric parameters give values of alpha in the range 1.1 to 1.4.