Some Atmospheric Turbulence and Stability Effects on Aerial Spray Penetration into Hardwood Forest Canopies

Abstract

Abstract Vertical profiles of wind, turbulence, and stability were measured in and above a partially foliated 16 m tall, oak forest during a series of single-swath, aerial spray trials. The distribution of cross-swath spray deposits was sampled after each application at the top of the canopy and below the canopy. Spray penetration to the canopy top and through the canopy was highly dependent on the relative intensity of mechanically generated turbulence (due to wind across a rough surface) to that of thermally generated turbulence (due to warm air rising) in the unstable roughness sublayer above the canopy. In conditions with mechanical turbulence dominant, termed mixed convection conditions (u* > 1 m s-1 and -0.01 > Ri > -1), the amount and consistency of material reaching the canopy top was higher than during periods with thermal turbulence dominant, termed free convection conditions (u* < 1 m s-1 and Ri < -1). A greater proportion of the material penetrated through the canopy in the free convection conditions. The relationship of the structure of the Reynolds stress in the roughness sublayer to the spray behavior is discussed. For. Sci. 42(1):93-101.