THE PREDICTION OF ATMOSPHERIC DIFFUSION BY USING AN EDDY DIFFUSIVITY BASED ON THE VERTICAL TRANSFER OF HEAT

Abstract

Vertical profiles of temperature up to 16 m and heat-flux data from Project Prairie Grass at O'Neill, Nebraska in 1956 have been used to compute the eddy diffusivity for the vertical turbulent transfer of heat. Assuming that heat and matter are transported by identical turbulent mechanisms, this diffusivity is then used to calculate vertical diffusion of sulfur-dioxide-gas clouds released at O'Neill. Satisfactory agreement is obtained between calculated and observed values. Assumption of a logarithmic wind profile near the ground and equivalence of the diffusivities for heat and momentum within this region leads to selection of a scale height below which the diffusivity for heat is independent of stability and above which the diffusivity depends upon the thermal stratification. This scale height is a function of surface roughness, and estimation of the roughness parameter provides a method of calculating the diffusivity in the absence of heat-flux measurements.