Large-eddy simulation of neutral atmospheric boundary layer flow over heterogeneous surfaces: Blending height and effective surface roughness

A new generation large-eddy simulation (LES), based on a Lagrangian scale-dependent dynamic subgrid model, is applied to neutral atmospheric flow over heterogeneous land surfaces. This LES is faithful to the physics of the interaction of the lower atmosphere and the land surface based on classical validation tests of the simulated mean wind profile and the atmospheric turbulence. Simulations of the atmospheric boundary layer (ABL) over heterogeneous land surfaces with a range of characteristic lengths and surface roughness values are performed, each simulated surface consisting of equal-size stripes of different roughness. The simulated mean wind profiles are analyzed to identify the height of the blending layer and used to develop a relationship between blending layer height and characteristic surface length scales. For hydrologic and atmospheric applications where the regional-scale surface roughness needs to be known, the analysis is extended to derive an effective surface roughness knowing local surface patch roughness values.