On relationships between urban and rural near-surface meteorology for diffusion applications

Dispersion of releases in urban areas can be estimated with information on micrometeorological variables in the urban boundary layer. However, this information is not generally available. On the other hand, meteorological measurements are routinely made in rural surroundings (e.g. airports). We examine empirical relationships between urban and rural meteorological variables using data from the Basel UrBan Boundary Layer Experiment (BUBBLE), conducted during June and July 2002 around Basel, Switzerland, and present two methods to estimate urban micrometeorology using measurements from rural sites. The first method is based on a two-dimensional internal boundary-layer model that uses rural variables as upwind inputs. It assumes that the urban Obukhov length is the same as that in the rural area in unstable conditions and that it is very large (neutral) in stable rural conditions. The second method uses a three-dimensional prognostic model called TAPM in which upwind rural observations are assimilated. Urban variables estimated from TAPM compare well with observations. This performance is slightly better than that of the internal boundary-layer model.