Preliminary results from an experiment on the interaction of a flow with an orographic relief

In this paper, the experiment is described and preliminary results from the analyses over all the measurement period and during an episode of katabatic wind are presented. Some kilometres downwind the obstacle, the katabatic flow takes up again the same direction and stability than upwind. However, the wind speed is seen to increase with respect to the speed measured upwind the obstacle. The ratio between turbulent and mean kinetic energy measured on the top of the obstacle, when plotted as a function of wind speed, clearly displays a considerable turbulent energy gain at high velocities and a bimodal data distribution in the range of mid velocities, suggesting a different behaviour of the flow as a function of stability.