A LAGRANGIAN STOCHASTIC-MODEL FOR AERIAL SPRAY TRANSPORT ABOVE AN OAKFOREST

An aerial spray droplets' transport model has been developed by applyi ng recent advances in Lagrangian stochastic simulation of heavy partic les. A two-dimensional Lagrangian stochastic model was adopted to simu late the spray droplet dispersion in atmospheric turbulence by adjusti ng the Lagrangian integral time scale along the drop trajectory. The o ther major physical processes affecting the transport of spray droplet s above a forest canopy, the aircraft wingtip vortices and the droplet evaporation, were also included in each time step of the droplets' tr ansport. The model was evaluated using data from an aerial spray field experiment. In generally neutral stability conditions, the accuracy o f the model predictions varied from run-to-run as expected. The averag e root-mean-square error was 24.61 IU cm(-2), and the average relative error was 15%. The model prediction was adequate in two-dimensional s teady wind conditions, but was less accurate in variable wind conditio n, The results indicated that the model can simulate successfully the ensemble average transport of aerial spray droplets under neutral, ste ady atmospheric wind conditions.