MEASUREMENTS OF WIND VELOCITIES IN A STREET CANYON

Measurements of winds velocities in an urban street canyon with a height-to-width ratio of about 1. 4 were made when ambient winds aloft were approximately perpendicular to the street. The mean wind velocities were determined by analysis of trajectories of tracer balloons that were released in the canyon and photographed in rapid sequence. The trajectories indicate the presence of a primary vortex cell within the canyon, provided the ambient wind velocity exceeds 1. 5-2. 0 m s** minus **1. Measurements with hot-wire anemometers suggest that vehicular traffic at the street level is significant in increasing turbulence up to heights of approximately 7 m.