Coupling Lagrangian surface layer and convective boundary layer models to describe aerial dispersal of particles released near the ground

The inadvertent introduction of exotic pathogens (such as the soybean rust pathogen) and the seasonal reintroduction to northern latitudes of diseases (such as tobacco blue mold) reinforce the need for better spore dispersal models because of the potential economic impact of local and inter-regional spread of plant diseases. Likewise, the extensive adoption of genetically modified crops has led to a need to better understand the dispersal of pollen in the atmosphere because of the potential for unwanted movement of genetic traits via pollen flow in the environment. In each case, pollen or spores must first escape from a plant canopy and enter the convective boundary layer (CBL) in order for long-distance transport to occur. The details of particle movement in and above the canopy can be adequately described by existing surface layer (SL) Lagrangian stochastic (LS) models, and these models can also be used to supply a lower boundary condition for an LS CBL model. A coupled SL and CBL LS model will be described. The coupling between these two models was accomplished by matching the first four moments of the PDF for the wind statistics at a matching height. The matching height was chosen by minimizing the differences in the four moments of the PDFs between the SL model (based on Monin-Obukhov similarity variables u* and L) and the CBL model (based on similarity variables w* and zi). Model predictions will be presented for deposition at distances of 1 - 5 km downwind from a source for a relatively small spore (Peronospora tabacina sporangia) and for a large pollen grain (Zea mays). The sensitivity of the coupled model to a variety of matching heights and matching conditions will be discussed.