Effects of land-surface heterogeneity on turbulent transport of momentum and heat: wind-tunnel studies

Land-surface heterogeneity affects turbulent fluxes of momentum and scalars (i.e., heat, moisture and trace gases). In particular, non-uniform momentum and scalar flux distributions are expected downwind of complex urban environments and steep topography, where flow separation, re-attachment and re-adjustment are the dominant mechanisms. Understanding the effects of surface heterogeneity on land-atmosphere interaction is important for developing new parameterizations of surface fluxes and for validation of advanced numerical models, such as Large-Eddy Simulation (LES) and numerical weather prediction (NWP) models. We conducted wind-tunnel experiments over a series of representative, idealized complex surface features, including 2D and 3D blocks, steep 2D and 3D hills, and canopy patches that were immersed in the lowest portion of thermally-stratified turbulent boundary layers. Thermally-stratified boundary layers were simulated by independently controlling the temperature of air flow, the test section floor, and the surfaces of the model topography. Spatial distribution of surface shear stress and heat flux in different flow regions will be presented and correlated to the dynamics of turbulent flow measured by high-resolution Particle Image Velocimetry (PIV) and x-wire/cold-wire anemometry.