Influence of Diurnal and Inertial Boundary- La Yer Oscillations on Long-range Dispersion

Coupled meteorological and Lagrangian particle models are used to examine horizontal dispersion over one to two diurnal cycles. Seven numerical experiments were run in which different portions of the atmospheric energy spectrum were included or excluded in the simulation of releases of a non-buoyant pollutant from an elevated point source. The results of the experiments indicate that vertical shear in the horizontal wind produced by diurnal and/or inertial oscillations in conjunction with or followed by vertical PBL mixing are capable of maintaining plume growth rates which are nearly linear with diffusion times up to 48 h. The mode! results agree reasonably well with long-range dispersion observations of an isolated smelter plume made in Australia. Periods of accelerating diffusion found in the simulations have also been indicated in observations. These accelerating diffusion periods in the simulations are due to time-dependent shear in the planetary boundary layer at night. Shear due to synoptic-scale horizontal temperature gradients was also found to have a significant impact on the modeled plume growth rates. Key word index: Boundary-layer model, Lagrangian particle model, long-range dispersion, wind shear, accelerating diffusion, inertia! oscillation, plume growth rates, meso~cale dispersion, geostrophic shear. bulence and synoptic-scale weather systems. With such a gap, horizontal growth rates which are linearly proportional to time can be maintained out to at most one hour. Gifford (1982) points to more recent observations of the atmospheric energy spectrum such as those of Gage (1979), which do not exhibit a spectral gap. as evidence of the presence of mesoscale energy