The urban surface layer in neutral conditions is studied based on an atmospheric wind tunnel simulation and velocity measurements by hot wire anemometry and stereoscopic PIV. First, the flow is characterized by one-point statistical quantities, such as mean velocity, Reynolds stresses and power spectra of the longitudinal component, as a function of height. The roughness parameters and the structure of the surface layer are also estimated. Then, maps of two-point correlations and quadrants of diagonal Reynolds stresses confirm the presence of coherent movements existing in models for the turbulence organization in smooth-wall boundary layers, from a certain height. Particular attention is devoted to the presence and the action of the transversal coherent movements which, coupled with the vertical coherent movements, participate to the flux transfer close to the canopy. Finally, the analysis of dynamics of the shear layer at the top of an obstacle shows a flapping behavior correlated with the intermittent shedding of vortex clusters from the obstacle, large-scale vertical coherent movements from the boundary layer penetrating the canopy layer and small scale coherent movements of ejection. This finding shows a mutual influence between the atmospheric boundary layer and the urban canopy flow.
