A note on the two‐dimensional equation of diffusion in the atmosphere

In this paper the shearing advection term, suggested recently by H. Lettau, is introduced into the well‐known two‐dimensional equation formulated by Sutton and Calder in their treatment of turbulent diffusion, and a solution of the ensuing equation is obtained subject to the conditions prescribed by the problem of diffusion from an infinite continuous line source, situated at ground level and orientated in a direction normal to that of the mean wind velocity. The predicted values of cloud height and peak concentration at a distance of 100 m downwind of the source, when compared with previous theoretical values and available experimental results in neutral stability conditions , show that no significant change in theoretical values is obtained by the introduction of Lettau's term, and the order of magnitude of the deviation from the Calder prediction produced by this term is found to be the same at all distances downwind of the source. The shearing advection term may consequently be ignored in the conditions investigated .