Virtually all atmospheric flows in nature are, to some extend, flows over rough surfaces with
roughness sizes from the sub-millimeter to meter scale. Roughness as an inherent feature of
the atmospheric boundary layer (ABL) enhances drag, mixing and transport properties of the
flow (w.r.t. pollutants, moisture, temperature . . . ). To study the effect of roughness on the
ABL, we perform direct numerical simulations (DNS) of the turbulent neutral Ekman flow over
rough surfaces. The lower boundary of the simulation domain is covered with fully resolved
three-dimensional cubical roughness elements of varying mean heights (small compared to the
boundary layer thickness).
In this poster, we display the logarithm of the magnitude of the passive scalar gradient to highlight the eddies in the boundary layer. At the same time, we want to emphasize the meaning of the small-scale roughness by showing two detailed views, the closest zoom-in even with the computational grid.