Advances in Atmospheric Sciences

Aerodynamic roughness length (z 0m) is a key factor in surface flux estimations with remote sensing algorithms and/or land surface models. This paper calculates z 0m over several land surfaces, with 3 years of experimental data from Xiaotangshan. The results show that z 0m is direction-dependent, mainly due to the heterogeneity of the size and spatial distribution of the roughness elements inside the source area along different wind directions. Furthermore, a heuristic parameterization of the aerodynamic roughness length for heterogeneous surfaces is proposed. Individual z 0m over each surface component (patch) is calculated firstly with the characteristic parameters of the roughness elements (vegetation height, leaf area index, etc.), then z 0m over the whole experimental field is aggregated, using the footprint weighting method.