The Characteristics and Parameterization of Aerodynamic Roughness Length over Heterogeneous Surfaces

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.