Determining aerodynamic roughness using tethersonde and heat flux measurements in an urban area over a complex terrain

Zero-plane displacement and aerodynamic roughness measurements were conducted using a tethersonde system in the third largest city in Taiwan. A method for determining the roughness under unstable conditions was developed. The resulting aerodynamic roughness and sensible heat flux were found to be very sensitive to a prescribed zero-plane displacement value. To minimize the uncertainty, the Bowen Ratio method was used to choose the correct sensible heat flux and zero-plane displacement values. Although the study site has the highest building height reported in the literature, its aerodynamic roughness value was determined to be 2.1 m, lower than values commonly cited for urban areas in the air quality community, while the zero-plane displacement value was found to be 35 m, the highest value reported in the literature.