SOME ATMOSPHERIC-TURBULENCE AND STABILITY EFFECTS ON AERIAL SPRAY PENETRATION INTO HARDWOOD FOREST CANOPIES

Vertical profiles of wind, turbulence, and stability were measured in and above a partially foliated 16 m tall, oak forest during a series o f single-swath, aerial spray trials. The distribution of cross-swath s pray deposits was sampled after each application at the top of the can opy and below the canopy. Spray penetration to the canopy top and thro ugh the canopy was highly dependent on the relative intensity of mecha nically generated turbulence (due to wind across a rough surface) to t hat of thermally generated turbulence (due to warm air rising) in the unstable roughness sublayer above the canopy. In conditions with mecha nical turbulence dominant, termed mixed convection conditions (u > 1 m s(-1) and -0.01 > Ri > -1), the amount and consistency of material r eaching the canopy top was higher than during periods with thermal tur bulence dominant, termed free convection conditions (u < 1 m s(-1) an d Ri < -1). A greater proportion of the material penetrated through th e canopy in the free convection conditions. The relationship of the st ructure of the Reynolds stress in the roughness sublayer to the spray behavior is discussed.