, Volume 66, Issue 1-2, pp 75-92

Turbulence close to a rough urban surface part II: Variances and gradients

Rent the article at a discount

Rent now

* Final gross prices may vary according to local VAT.

Get Access

Abstract

Measurements of the turbulent wind and temperature fluctuations were carried out in the vicinity of the roof level, over an urban surface at a site where mean gradients of wind speed and temperature were also available. The measurement heights were about 23 and 28 m above ground, the local roof level being 18 m. Measurements were taken on top of a building (at (z=23 and 28 m) and over a street canyon (atz=23 m), i.e., fully within the urban roughness sublayer.

The scaled variances of temperature and wind velocity, as well as the non-dimensional gradients of wind speed and temperature, are presented and discussed in terms of departures from Monin-Obukhov similarity theory. Local scaling is found to be a useful concept for the description of turbulence within a roughness sublayer. Expressions for the scaled velocity variances are presented that are valid for all measurement positions; they compare well with results from other urban studies. The non-dimensional gradient of mean wind speed is found to be well represented by the semi-empirical functions for the inertial sublayer if locally scaled. At 5 m above roof level, however, the variability due to horizontal inhomogeneity becomes very large. The non-dimensional temperature gradient, on the other hand, is height dependent and not well defined over the present rough urban surface.