Short-range diffusion experiments in unstable conditions over inhomogeneous terrain

Abstract

Equipment to measure the dispersion of a release of the tracer sulphurhexduoride (SF6) was developed and nine experiments were then performed at the Rise National Laboratory in the period April to July 1976. The tracer was released at 60 m from the Ris0 meteorological tower, situated on a peninsula in the Roskilde Fjord, Denmark, and was sampled at ground-level positions distributed over a crosswind line about 1 km downwind. During the experiments, the turbulent wind velocity components were measured at the height of release with a threedimensional ultrasonic anemometer. The experiments were performed in westerly winds, hence the dispersion was influenced by the internal boundary layer developing downwind from the inhomogeneity in surface roughness between the fjord and the site. Five of the experiments, performed in neutral and slightly unstable conditions, were accepted as cases of purely turbulent dispersion of the tracer. Because of wind direction shifts the others were discarded.The concentration measurements allowed a direct estimate of the lateral dispersion parameter 0 , . The Taylor diffusion formula using the wind velocity measurements at the height of release was found to work well in predicting uy, despite the fact that shortcomings in fulfilling the requirements for its application existed. uy, predicted by an empirical formula characteristic for an open area (Bultynck and Malet, 1972), was found to be systematically larger than the experimental value. Excellent agreement was found by multiplying the predicted 0 , . values by the factor 0.6. This indicates that the effect of surface roughness can be separated from the effect of stability.Because the estimates of the vertical dispersion parameter, u,, were only indirectly inferred from continuity considerations, they could not, although fair agreement was obtained, be used to check the validity of calculating u, from Taylor's formula or from the empirical formula mentioned above.

Description and validation of ERAD: An atmospheric dispersion model for high explosive detonations

“…Although there is overwhelming observational evidence of the non-Gaussian nature of the vertical dispersion, systematically nowGaussian distributions are not observed in the case of lateral diffusion (Deardorff and Willis, 1975;Gryning et al, 1978;Nieuwstadt and van Duuren, 1979;Gryning and Lyck, 1980;Eberhard et al, 1988). The lateral dispersion may be viewed as the combined effect of turbulence and shear in the wind direction (section 5.5).…”

An experimental study of momentum and heavy particle transport in a trellised agricultural canopy

“…Raynor et al (1970) defined the plume width as the distance between the points on either side of the centerline where the concentration dropped to 10% of the centerline value. Others who had sufficient data density determined the spanwise standard deviation of the plume (σ y ) by its statistical definition (e.g., Gryning et al, 1979;Peterson et al, 1999;Yee et al, 2006). Skelsey et al (2008) and Prussin et al (2014)…”