Large-Eddy Simulations of Convective Boundary Layers over Flat and Urbanlike Surfaces

The effects of urbanlike surfaces with a block array on the dry convective boundary layer (CBL) are numerically investigated using the parallelized large-eddy simulation model. Five cases representing a free CBL, a sheared CBL, and a strongly sheared CBL over flat surfaces, a sheared CBL over a block array, and a sheared CBL over a modeled canopy layer are simulated and compared. In the sheared CBL over a block array, mixed-layer flow is decelerated because of increased surface shear and horizontal convective rolls appear in the mixed layer. In contrast, convection cells and intermediate structures between cells and rolls occur in the free and sheared CBLs over flat surfaces, respectively. Horizontal convective rolls and the traces of block-induced turbulent eddies are detected in the spectral density fields of vertical velocity and in the vertical profiles of vertical velocity skewness in the sheared CBL over a block array. The decelerated mixed-layer flow in the sheared CBL over a block array le...