Incorporating zero-plane displacement in roughness length estimation and exposure correction factor calculation

Abstract

Exposure correction is necessary for removing the distortion effects induced by nonstandard local exposure in raw near-ground wind speed datasets. The accurate calculation of the exposure correction factor ($\mathrm{ECF}$) for wind speeds requires reliable input of the local aerodynamic roughness length ($z_0$). In this study, we evaluate the performance of an $\mathrm{ECF}$ formula suggested by the World Meteorological Organization and the estimation of $z_0$ based on gustiness model. The estimation of $z_0$ will be more reasonable if local zero-plane displacement ($z_d$) is considered under rough terrain conditions. An empirical linear relationship $z_d=C_0{z}_0$ is introduced, and the ratio $C_0=6$ is recommended for meteorological stations under rough terrain conditions in China coastline. The incorporation of $z_d$ into the $\mathrm{ECF}$ formula suggested by the World Meteorological Organization is further performed. Sensitivity analyses indicate that the $z_0$ estimates and $\mathrm{ECF}$ values are highly sensitive to factors such as mean wind duration, gust duration and anemometer height. Finally, we conducted case studies across 15 meteorological stations in China coastline, which revealed that our proposed method enhances the accuracy of both $z_0$ estimation and $\mathrm{ECF}$ calculation in comparison to the existing models.