Measurements of Air Turbulence in Reading and their Relation to Turner's Stability Categories

Continuous air turbulence measurements were made near the centre of the town of Reading for a period of one year. These were intended to provide data for deriving diffusion parameters for calculating the dispersion of pollution from chimneys in the town. They were obtained by using a bivane mounted on a 14 m mast, and the intensities of lateral and vertical turbulence for 1 h periods were derived by means of electronic analysers. Similar measurements were made for a period of about 4 weeks on the roof of a building at the B.P. Research Centre, Sunbury-on-Thames. The values of intensity of turbulence were grouped according to Turner's stability categories and the averages within the groups were compared by variance analysis. This showed significant differences in turbulence between the unstable categories and the neutral category, but the stable categories were not distinguished from neutral. The addition of a filter to cut out the high frequency band of the fluctuations showed that a considerable portion of the measured turbulence had been in this band and this is attributed to mechanical turbulence produced by the surrounding buildings. Eliminating the high frequency band also distinguishes the stable categories from neutral. The measurements of intensity of turbulence have been used to estimate the spread of plumes in the town. The lateral spread is greater than that published by other authors but the vertical spread is similar.