Evaluation of the turbulent parameters of the unstable surface boundary layer outside Businger's range

The dispersion coefficient, σ_z, involves two important turbulent parameters, the friction velocity and the Monin-Obukhov length. We have used Businger's universal functions to compute those parameters which were developed within the range, − 2 ⩽ z / L ⩽ 0. Our purpose is to show that Businger's universal functions perform well outside that range. Correlation coefficients are satisfactory when the roughness length is used as a key to detect good runs. A wider range can be considered and given as follows: − 8 ⩽ z / L ⩽ 0. Two different ranges are defined and given by 3.3 ⩾ z₀ ⩾ 0.4 cmand 6.1 ⩾ z₀ ⩾ 0.2 cm. The iteration method used in this paper can be considered to be quickly convergent and computationally efficient, except for free convection.