The adjustment of profiles and eddy fluxes

Abstract An assessment is made using simple diffusion theory of the rate of adjustment of profiles and eddy fluxes for (a), the leading‐edge case as a function of distance and (b), the horizontally uniform case as a function of time. The solutions of the appropriate diffusion equations obtained by Philip (1959) are used as the basis of the calculations. For the leading‐edge case the fetch‐height ratio for 90 per cent of the adjustment to be completed varies from 140 at a height of 0·5 metres to 530 at a height of 50 metres. The solution has application over a wide range of wind speed. For the case of horizontal uniformity and following an abrupt change in surface flux, 90 per cent of the adjustment is completed in 0·45 min at a height of 0·5 m increasing to 86 min at a height of 50 m. It is suggested that these values indicate that the choice of site and conditions for micrometeorological research is critical, and that disparity between a number of experiments may be a consequence of failure to satisfy these basic requirements.