A LABORATORY EXPERIMENT ON LATERAL DIFFUSION OF SCALAR QUANTITIES IN THE STRATIFIED SURFACE-LAYER

Based on a local gradient concept and vertical eddy diffusivity coefficient K//D//z presented in a previous paper buoyancy effects were evaluated at the same nondimensional vertical distance from the wall. The results indicated that the ratio of the vertical diffusion coefficient under diabatic conditions to its value in neutral conditions, expressed by a shear function, agreed well with observations by J. A. Businger et al. Although the ratio K//D//y/K//D//z in the neutral condition was found to be 1. 5-2. 0 in the fully turbulent region, increasing to a value more than 10 in the vicinity of the wall, this ratio in the stratified conditions, when normalized by the neutral value, could be correlated by only zeta ( equals z/L; L being the Monin-Obukhov length); it increased with zeta in the stable condition, while in the unstable condition it remained almost unity. However, in extremely unstable conditions it decreased rapidly.