Urban Application of an Alternative Flux Estimation Method

Momentum and temperature fluxes computed using horizontal and vertical speed (s,w) are compared to fluxes computed using traditional fixed and rotated coordinate systems. The sw method eliminates wind direction trend effects and permits a simple tilt to a zero mean vertical velocity without creating undesirable residuals. Spectra and cospectra obtained using the new and conventional flux estimation methods are compared using 3D sonic anemometer data from the Oklahoma City(JU03) experiment. Fluxes are then evaluated for statistical significance using a test based on spectral coherence. The sw method and spectral coherence test provide useful insights into turbulent transport in complex urban canyon flows.