Characterization and Comparison of Aerodynamic Roughness Lengths Using Ground-Based Photography and Sonic Anemometry: Fid-Bau Portal

Characterization and Comparison of Aerodynamic Roughness Lengths Using Ground-Based Photography and Sonic Anemometry

Lombardo, Franklin T. / Krupar, Richard J.

In this study, two methods used to estimate surface terrain conditions ( $z_{0}$ ) surrounding Automated Surface Observing System (ASOS) stations in tropical cyclone-prone regions were analyzed. The first method utilized ground-based photography from the National Oceanic and Atmospheric Administration Hurricane Research Division’s Tropical Cyclone Wind Exposure Documentation Project (WEDP). The second applied a modified effective $z_{0}$ method using ASOS wind data. Comparisons reveal that WEDP $z_{0}$ estimates are typically larger in magnitude and do not account for changes in upstream $z_{0}$ . Variability in the $z_{0}$ estimates showed a distinctly skewed nature in the probability distributions, which may have some physical meaning. It was also shown that standardized maximum 1-min sustained wind speeds using both the WEDP and MM2010 median $z_{0}$ estimates for short fetch lengths can have differences as large as 15%. The MM2010 $z_{0}$ estimates were also compared with single weighted mean $z_{0}$ estimates to be incorporated in the next version of the U.S. wind loading standard and suggest that a single weighted mean $z_{0}$ value does not effectively capture the variability of the terrain with respect to wind direction.