Wind tunnel experiment on turbulent diffusion suppression by row covers

Effects of row covers on turbulent diffusion of scalar entities (e.g., sensible heat, latent heat, CO2) from within the canopy to the atmosphere or vice versa were investigated using a wind tunnel. Wooden cylinders were used as models of vegetation. Three kinds of non-woven fabrics were placed directly on the wooden cylinders. CO2 was chosen as a tracer gas and was released from a line source at the floor of the wind tunnel. From the profiles of CO2 concentration and the profiles of horizontal CO2 concentration gradients at a position downward from the line source, the turbulent diffusion coefficients and turbulent diffusion resistances were calculated. The results showed that the turbulent diffusion within and just above the canopy was remarkably suppressed by the row covers. The degree of suppression was greater with smaller porosity of the cover. (C) 1997 Elsevier Science B.V.