An analysis of the circulation characteristics and energy budget of a dry, asymmetric, east-west urban canyon. I. Circulation characteristics



Wind characteristics within urban canyons are of considerable significance for pollution diffusion, for assessing the nature of the atmospheric environment at street level, and in determining the energy budget of the canyon. This study presents an analysis of the circulation characteristics for a deep, east-west, asymmetric urban canyon (located in Columbus, Ohio, USA), based on measurements of ambient wind at roof level, vertical velocities at the canyon-top, and within-canyon horizontal winds. Canyon-top vertical velocity was normally directed upward, even with cross-canyon winds, indicating along-canyon horizontal convergence. Its speed was approximately related to the magnitude of the southerly, easterly, and westerly components of the roof-level wind. Three-fifths of the data sets showed evidence of a vortex circulation superimposed upon the mean vertical motion, although its speed and direction were not clearly related to the direction of the cross-canyon wind. Some of the perplexing aspects of the results may be attributable to the asymmetric structure of the canyon. Overall, these results suggest that wind fields within and above urban canyons may not be as simply as empirical studies hitherto have suggested and that attempts at modelling these characteristics of the urban climate must recognize this.