Wind-profile measurements above a maize crop

An experiment of wind-profile measurements above a maize crop was described. First the mean ratio between the height of the adapted layer and the fetch was deduced from profile measurements at several positions in the field. The height-to-fetch ratio amounted to 1/64. Because of too small a fetch, the vertical transport of momentum between the maize crop and the atmosphere could not be estimated accurately enough from the windprofile measurements only. The parameters of the assumed logarithmic wind profile, the zero-plane displacement and the roughness length, could only be estimated from a comparison of wind-profile measurements with simultaneous eddy-correlation measurements. In the present experiment, the zeroplane displacement d and the roughness length z₀ could be expressed in the height h of the full-grown crop as d = 0.5 h and z₀ = 0.11 h, respectively. The application of a common empirical relationship from the literature (e.g. d = 0.6 h ) led to considerable systematic errors of the estimated friction velocity above maize.