An extended similarity theory for the stably stratified atmospheric surface layer

An advanced similarity-theory formulation for the wind and temperature prof iles in the stably stratified atmospheric surface layer (ASL) is developed with due regard to the effect of the free-flow static stability on the ASL. In the revised log-linear profiles, empirical coefficients traditionally c onsidered as universal constants, namely the slope factors in the z-less st ratification layer (beyond the logarithmic sub-layer), become functions of the dimensionless number S = NL/u(*). Here, N is the Brunt-Vaisala frequenc y in the free flow, L is the Monin-Obukhov length, and u(*) is the friction velocity. The number S indicates how strongly the ASL is affected by the f ree-flow stability. This new formulation leaves room for the occurrence of well developed turbulence at much higher Richardson numbers, Ri, than had b een suspected. Moreover, it results in a pronounced dependence of the turbu lent Prandtl number on Ri in a wide range of Ri, including the z-less strat ification layer, in correspondence with long-standing empirical evidence. T he traditional Monin-Obukhov similarity theory disregards the above essenti al features of the stably stratified ASL. New data from measurements over a slightly inclined plateau in West Greenland provide experimental support f or the proposed theory.