Mean and turbulent motion in and above a canyon

F i e l d measurements and wind tunnel simulations of a canyon wind have been conducted. It is found that the main characteristics of the vertical distribution of the mean canyon wind are : (1) a strong jet flow fills the entire depth of the canyon, (2) a change in wind direction at about the canyon top, and (3) a comparatively weak return flow of about the same depth as the canyon jet occurs above the canyon top with its maximum about 25% of the maximum of the canyon jet. Simulation of the canyon flow in the wind tunnel reveals similar characteristics in the mean velocity profile measured in the canyon. It is also found that the maximum intensities of the longitudinal and vertical components of the turbulent motion as well as the vertical eddy transport of longitudinal momentum occurs near the maximum shear of the mean velocity in the flow. By assuming similarity between the flows in the canyon and wind tunnel, estimations are made of the maximum intensities of the longitudinal and vertical components of the turbulent motion and the vertical eddy transport of longitudinal momentum in the canyon.