Surface flux parameterization for use in atmospheric global climate models

A new analytic approximate solution is presented for the Monin-Obukhov similarity equations in unstable atmospheric conditions. Stability functions that are well supported by observations are used for this study. The difference between momentum (zom) and heat (zoh) roughness lengths is fully taken into account. A new parameterization is also presented for the free-convective boundary layer based on a natural extension of the standard Monin-Obukhov similarity theory. A current parameterization scheme is modified in order to meet some requirement of free convection and then a non-iterative solution is developed. The proposed analytic solution can replace costly numerical iterative methods used for estimating surface fluxes and related turbulence characteristics. The avoidance of iteration can speed up computations in large-scale models considerably (up to 10 times) and cases that do not converge or converge very slowly cannot occur. The performance of the new solution in unstable atmospheric conditions is compared and found to have very good match with the fully iterative solution for a wide range of the stability parameter zL , and other parameter values of the height z, and roughness lengths zom and zoh. Comparison is also made with some of the different solutions proposed in the literature. In the free-convective conditions too the new non-iterative solution gives good results for many realistic combinations of the parameters.