Poster EGU Turbulent transfer is one of the most important processes in the Atmospheric Boundary Layer (ABL), showing many difficulties in stable situations (SBL): non stationary conditions, presence of internal gravity waves, intermittency, decoupling from the surface fluxes, etc. • The Monin-Obukhov (M-O) Theory is a suitable framework for presenting micrometeorological data, as well as for extrapolating and predicting certain micrometeorological information where direct measurements are not available. • In order to describe the surface fluxes, which is a key parameter in the atmospheric and dispersion models, the universal similarity functions fm and fh for non dimensional wind and temperature profiles must be determined [1]. • Some commonly used linear universal functions can be not valid for moderate to strong stability, leading to important errors in the evaluation of surface fluxes. What is the range of validity?