Effect of sub-layer corrections on the roughness parameterization of a Douglas fir forest

This study investigated two aerodynamic methods to estimate the momentum roughness length and displacement height (z0 and d0 respectively) of a 32 m-tall Douglas fir forest using simultaneous micrometeorological and flux measurements. When the flux–gradient method was used to objectively determine z0 and d0, corrections for roughness sub-layer effects proved to be important. A new iterative method is employed to solve the set of equations when the corrections were made. The estimated average values of z0 and d0 with corrections vary from 1.2 m to 1.4 m and from 26.2 m to 28.4 m respectively depending on the correction method applied. In the absence of experimentally determined roughness sub-layer height, the corrections of Harman and Finnigan (2007) yielded the best overall estimates of aerodynamic parameters.