Optimized computation of transfer coefficients in surface layer with different momentum and heat roughness lengths

A new method for computing the surface transfer coefficients is proposed, based on state-of-the-art empirical flux-profile relationships. The influence of the roughness length ratio is first demonstrated with the classical iterative calculation method. Then a non-iterative algorithm is developed, taking into account the difference between momentum and heat roughness lengths. The new method is validated by comparison with the reference iterative computation. The large gain-in computer processing time (CPU) time gain for the calculation of surface fluxes in Eulerian grid models is finally assessed.