Interazione tra correnti di pendio ed isola urbana di calore

An experimental study about two-dimensional upslope and downslope flows in a stably stratified environment and about their interaction with an urban heat island placed in a valley is presented. Two different configurations are reconstructed in a laboratory model: an open valley at the bottom of a slope and a valley closed between two symmetric slopes. The slope flows are generated heating or cooling the slopes by Peltier cells. The urban heat island is simulated by an electric resistance placed within the valley. The main features of the circulation driven by the thermal exchanges are studied using an image analysis technique, named Feature Tracking, that allows a Lagrangian reconstruction of the motion. The distributions of the velocity and of its second order statistics along some profiles are displayed; the temperature profiles are obtained from measurements with thermocouples. The experimental tests display that the slope flows affect strongly the urban heat islands in both configurations: in the open valley the urban heat island is strongly deformed and nearly destroyed by the slope flow and a recirculating zone takes place; in the closed valley the urban heat island circulation is weakened by the anabatic flows and it is enhanced by the katabatic flows.