Changes of the displacement height and roughness length of maize during a growing season

Variations in the displacement height (d) and roughness length (z0) of a maize crop were investigated through a growing season. A programme of measurement from which the wind profile, the Richardson gradient number and the turbulent fluxes of heat and momentum were estimated, was carried out. Two techniques were combined to obtain unique values for d and z0: the log-profile fitting technique and the eddy correlation technique. Throughout the growing season, the displacement height appeared to correlate very well (r = 0.98) with the height (H) of the canopy. A mean value for d/H was 0.75. The roughness length was strongly correlated with the difference between the canopy height and the displacement height. A mean value of 0.26 for z0/(H − d) was found (r = 0.86). If the ratio d/H was fixed, the roughness length did not show any clear dependence on wind speed or thermal stability.

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