In many urban turbulence studies, sonic anemometers are deliberately placed in the inertial sublayer, well above the roughness elements, in part to avoid the problems of interpreting data from within the urban roughness sublayer. The need to accurately predict dispersion within urban areas for air quality modeling and emergency response requires detailed knowledge of turbulent statistics and improved scaling schemes for data taken within urban roughness sublayers. The data from urban canyon studies have been difficult to interpret, and conflicting results can be found in the literature.

One problem is that the vertical surfaces which define the urban canyons also produce drag. The standard method of calculating u* from u'w' and v'w' does not capture the full amount of momentum lost to surfaces within urban canyons because, in streamwise coordinates, the momentum flux for flow along a vertical surface is expressed as u'v'. Inclusion of u'v' is made with a Reynolds stress tensor derived analog to u*. The performance of this u* analog is compared to u* for use in scaling urban flow within and immediately above an urban canyon in Oklahoma City during JU2003 as well as in neighboring street intersections. This u* analog is shown to be a useful tool for better understanding urban roughness sublayer flows.