Fluctuating plume model

The dispersive contributions due to plume spreading (given by and Z ) are statistically independent of the contributions due to plume meandering (given by 5 and 5 ). The fluctuating plume model is depicted in Fig. 3. 

For the fluctuating plume model, the simple addition of the solutions for sources at altitudes h and —h will not accomplish reflection because the asymmetries due to plume meandering must also be reflected in the fictitious image source at -h. The correct reflection for the fluctuating plume model is... 

The Offshore and Coastal Dispersion (OCD) model (26) was developed to simulate plume dispersion and transport from offshore point sources to receptors on land or water. The model estimates the overwater dispersion by use of wind fluctuation statistics in the horizontal and the vertical measured at the overwater point of release. Lacking these measurements the model can make overwater estimates of dispersion using the temperature difference between water and air. Changes taking place in the dispersion are considered at the shoreline and at any points where elevated terrain is encountered. 

Gifford, F. A, 1984, Statistical Properties of a Fluctuating Plume Dispersion Model Advances in Geophysics 6 Academic Press, NY, p 117. 

TLTPOS is a Gaussian model tluit estimates dispersion directly from fluctuation statistics at plume level. 

Gifford, F. A. (1959). Statistical properties of a fluctuating plume dispersion model. Adv. Geophys. 6, 117-138. 

The dilution in air due to the atmospheric dispersion of radioactive aerosols resulting from a release of radioactive material was modelled for positions along the centre line of the plume using the diffusion equation with a top hat distribution to account for the directional fluctuations in crosswinds ... 

This review has mainly focused on models for mean concentrations. However, fluctuations need to be estimated in order to assess all the risks associated with accidental releases. There is some evidence from the experiments, Davidson et al., 1995 [143], that the intensity of fluctuations is lower in clouds/plumes released among buildings, and are also qualitatively different. There is much less chance of a large scale of wind gust reducing the concentration to zero, so that the probability density function is closer to a log-normal distribution than to a cut-off Gaussian (Mylne, 1992 [440]). 

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