Roughness length parameterisation in urban boundary layers

In an attempt to develop an improved model for the wind-speed profile valid for urban boundary layers, the role played by the roughness length z
0
, i.e., the constant of integration of the vertical gradient of the wind speed, is extended. z
0
is assumed here as a ‘dynamic’ variable rather than as a ‘geometric’ parameter independent of the flow properties. On the basis of experiments conducted in a park located within the city of Rome and in the laboratory, it is found that in neutral conditions the ‘vertical’ profile of the roughness length shows a nearly exponential decrease with height.

Keywords: Monin-Obukhov similarity theory, MOST, similarity, boundary-layer, canopy layer, buildings, displacement height, inertial sublayer, ISL, urban heat island, roughness length, CEDVAL