Similarity relations in a stable and relatively neutral surface layer in an urban area with complex topography (Tehran)

In this paper the flow and turbulent structures are investigated over the city of Tehran (an urban area located in a basin surrounded by high mountains in the north and east). A number of non-dimensional parameters are investigated in the frame work of Monin–Obukhov similarity theory (MOST) using a local scaling approach. These parameters include dimensionless wind gradient, normalized standard deviations of three components of wind and dimensionless momentum fluxes. The main purpose of this paper is to evaluate MOST in predicting the above parameters for the selected terrain at 15 and 105 m heights. The prevailing conditions are stable and relatively neutral, based on stability parameter using local Obukhov length. For this study, data of a PA1 SODAR with supplementary data of a 100-m tower with four 2D sonic anemometers and also a 2D sonic anemometer installed at 2 m height have been used. Our results confirm that the non-dimensional parameters could be collapsed in to the similarity expressions only at 105 m height (that lies in the inertial sub-layer) not at 15 m height (that belongs to the roughness sub-layer). It is important to note that the obtained empirical constants for all of the considered parameters show considerable differences with those reported by others for other surface types. This is attributed to the local effects for where that the topographic wave forcing may need special considerations. This robustly emphasizes the importance of MOST validation for urban area with topography as Tehran. Consequently, MOST has been successfully verified at 105 m for Tehran data set with new empirical constants.