Abstract
The vertical turbulence structure in an above and urban canopy layer wereobserved in Sapporo city, Japan in July 1991, and November 1992.
Profiles of velocity fluctuation at, and Reynolds stress uw increased with height up to 1.5 h (h=7m, his the canopy height), and both had peaks at 1.5 h above the canopy, then from there decreased with increase in height. Sweep events, in which high velocity fluid from above move downwards toward the surface, and ejection events, in which low velocity fluid from below move upwards, occurred intermittently in and above the canopy. Profiles of the sweep had a large value under the 3 h, and the ejection had a peak between 1.5-3 h above the canopy. It shows the existence of coherent structure above the canopy. Peaks of σu and uw at 1.5 h were caused by the coherent structure above the canopy. The height of the roughness sublayer, that is, the height in which the buildings have a direct influence in the flow, was ap proximately 3-4 h.
