1Roughness length and zero-plane displacement over boreal, cool-and warm-temperate 2 forests were observed and parameterised using forest structure data. Previous mod-3 els for roughness length and zero-plane displacement using leaf area index and 4 frontal area index did not describe intersite differences, and the model for zero-5 plane displacement did not express seasonal variations with the change of leaf area 6 that was smaller in dense forest than in sparse forest. The observed results show 7 that intersite differences of normalised zero-plane displacement were related to stand 8 density, and seasonal variations were related to leaf area index at each forest, with 9 the degree depending on stand density. From these observations, a new concept is 10 proposed for normalised zero-plane displacement: the basal part is primarily de-11 termined by the density of stems and branches (stand density), while the seasonal 12 variation depends on the density of leaves (leaf area index), which is limited to

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We used an aerodynamic method to objectively determine the representative canopy height, using standard meteorological measurements. The canopy height may change if the tree height is used to represent the actual canopy, but little work to date has focused on creating a standard for determining the representative canopy height. Here we propose the 'aerodynamic canopy height' h a as the most effective means of resolving the representative canopy height for all forests. We determined h a by simple linear regression between zero-plane displacement d and roughness length z 0 , without the need for stand inventory data. The applicability of h a was confirmed in five different forests, including a forest with a complex canopy structure. Comparison with stand inventory data showed that h a was almost equivalent to the representative height of trees composing the crown surface if the forest had a simple structure, or to the representative height of taller trees composing the upper canopy in forests with a complex canopy structure. The linear relationship between d and z 0 was explained by assuming that the logarithmic wind profile above the canopy and the exponential wind profile within the canopy were continuous and smooth at canopy height. This was supported by observations, which showed that h a was essentially the same as the height defined by the inflection point of the vertical profile of wind speed. The applicability of h a was also verified using data from several previous studies.

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