Effect of wind fluctuations on near-range atmospheric dispersion under different types of thermal stratification

When using the mean wind direciton in Reynolds-averaged Navier-Stokes (RANS) simulations of atmospheric dispersion, it is well documented that peak concentration levels are often overestimated, and lateral spreading underestimated. Recently, it has been illustrated for neutrally stratified boundary layers that simulations improve significantly when the effective variability of wind directions, obtained by reducing the variability observed in experiments with the fluctuations predicted in the RANS turbulence model, is included in the boundary conditions. In the current work, we extend this approach towards thermally stratified boundary layers. We test the approach by performing a series of dispersion simulations of the Project Prairie Grass experiments, and demonstrate that also under these conditions the simulations improve markedly.