Effects of terrain roughness on downburst wind profile characteristics

Terrain roughness is an important index of reflecting ground undulation and shape in the atmosphere boundary layer, and is also the key factor affecting the near-ground wind field characteristics. In order to study the effects of terrain roughness on downburst wind profiles characteristics, a three-dimensional full-scale downburst model was established and validated by physical experiments. The variable terrain roughness was achieved by compiling program to adjust the uniform roughness element height and distribution density. The downburst wind fields with variable terrain roughness were numerical simulated. The results indicate that, at a close position from the center of the storm (r ≤ 1.0D_jet), the effects of surface roughness for downburst wind field are not significant. The value and position of the maximal wind velocity are hardly affected by the terrain roughness. With the downburst impacting the ground and diffusing along the radial direction, the energy dissipation is significantly affected by the surface roughness, resulting in different vertical wind profile characteristics at different terrain roughness. The radial wind profiles are affected evidently by the terrain roughness near the ground, and it has a large range of affected area. The wind velocity of the downburst in the radial direction decreases rapidly as the rough length of the ground increases. With the height from ground increasing, the affected area of terrain roughness in the radial wind profile are mainly reflected far from the center of the storm. Although there is a natural intensity attenuation process in the radial diffusion, the near ground strong wind induced by the downburst is still threatening and destructive. The effect of ground roughness on the downburst wind profile cannot be ignored. It is necessary to consider the correction of terrain roughness in the downburst wind profile model.