Thursday, 18 July 2002
Dispersive vs. Local Turbulence Statistics Within the Urban Roughness Sublayer.
Dispersive vs. Local Turbulence Statistics Within the Urban Roughness Sublayer. Submitted to: 15th Conference on Boundary Layer and Turbulence, Wageningen, Holland, July 2002
E. Gavze, E. Fattal, S. Pistinner Israel Institute for Biological Research, P.O.B 19, Ness-Ziona, 74100, Israel
Turbulence measurements were conducted on two roofs and in the street between them in a city in Israel during the summer time, deep within an urban fetch. Three pairs of ultrasonic anemometers were deployed above the main roof top, each of which was mounted at a heights of 2 and 6 meters above the roof level. The pairs were seven meters apart from each other, thus occupying a third of the roof length. The roof height was roughly 10 meters above the street level, so that in terms of normalized heights the measurements were performed at 1.2 and 1.6. Another anemometer was mounted on an adjacent roof upwind on the same height above the roof level as the highest anemometers downwind. Thus the separation between the most distant anemometers was roughly 30 meters. The sampling rates of each anemometer was 10Hz and data were collected on the same card to ensure synchronization.We find that the so called 'dispersive terms' are generally much smaller than the local terms. The 'dispersive vertical momentum fluxes' are a few orders of magnitude smaller than the local fluxes. The direction dispersive fluctuations are about 20% of the spatial average of the local fluctuations. Thus, to the first order, the contribution of these terms to pollutant transport may be neglected.
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