The Effect of Wind Direction on Particle Transport in a Trellised Agricultural Canopy

Natural and agricultural plant ecosystems are strongly influenced by turbulent particle trans- port. The dispersion of particles in canopies has received considerable attention from re- searchers, but near-source dispersion in trellised crops specifically has not. To address this issue, we conducted field experiments in a commercial vineyard near Monmouth, Oregon during the fall of 2011 and 2013. Particle dispersion was studied by releasing inert fluorescent microspheres within the canopy. The microspheres had a similar size and mass to multiple natural particles of interest in vineyards including the spores of Erysiphe necator and of Botrytis cineria. Wind velocity data from a meteorological tower used in both years demonstrated that the majority of the flow in the canopy was channeled into the vine row direction, regardless of the above-canopy wind direction. The shape of the particle plume was highly influenced by this channeling of the flow. Based on the 2011 data, we developed a new skewed Gaussian plume model that accurately described the particle plume when winds at five meters (2.5x the canopy height) were within ±15° of being aligned (i.e. parallel) with the rows. In contrast, it was more difficult to describe the plume when winds where nonparallel to the vine rows. In order to further examine the effect of nonparallel wind flows on particle dispersion an expanded sampling array was used for the release events in 2013. Data from both years shows that the turning of the wind profile impacts the plume more significantly than expected leading to poor performance of algebraic plume models.