Wind direction dependence of atmospheric boundary layer turbulence parameters in the urban roughness sublayer

Abstract

A variety of atmospheric boundary layer parameters are examined as a function of wind direction in both urban and suburban settings in Oklahoma City, Oklahoma, derived from measurements during the Joint Urban 2003 field campaign. Heterogeneous surface characteristics result in significant differences in upwind fetch and, therefore, statistically significant differences in measured values, even for small changes in wind direction. Taller upwind obstructions yield larger measured values of drag coefficient and turbulence intensity than do shorter upwind obstructions regardless of whether the obstruction is a building or a tree. The fraction of turbulent kinetic energy going into streamwise, cross-stream, and vertical variances differs depending on the upwind fetch, and reduced cross-stream values may indicate locations of persistent wind stream convergence. In addition, a quadrant analysis of burst/sweep behavior near the surface is examined as a function of wind direction in urban and suburban environments.