An experimental investigation of some methods of estimating turbulence parameters for use in dispersion models

The standard deviations of wind fluctuations in the horizontal and vertical directions, σ_θ and σ_φ, are now used in some pollution dispersion models to estimate the plume spread parameters σ_y and σ_z. Methods exist for estimating σ_θ and σ_φ when direct measurements are unavailable, using routine weather observations or wind measurements and temperature profiles from meteorological towers. In this paper such estimates are compared with direct measurements made at a height of 56 m, for a sampling time of 1 h, for a range of meteorological conditions. The work was carried out at a site in relatively irregular terrain. This was flat to rolling with a mixed surface cover within 1 km of the tower, with hills rising beyond that distance. Profile measurements were made with robust instruments rather than research grade sensors.Estimates of σ_φ made during the daytime agreed well with measurements, with a bias in the estimates of less than 0.4°. The r.m.s. differences between estimates and measurements were 1.1° (profile method) and less than 2° (routine weather observations method). Daytime σ_θ estimates were generally too low (bias 5–6°), although they were positively correlated with the measurements. At night σ_θ, was severely underestimated, and σ_φ was also underestimated.