Wind input data for urban dispersion modeling – Activities of Working Group 1 within COST 715

In 1998, the European COST action 715 on ‘Meteorology Applied to Urban Air Pollution Problems’ was initiated and in the mean time 15 countries have signed the contract. The overall goal of this COST action is to ‘...increase knowledge of the main meteorological parameters which determine urban pollution levels’. The present contribution focuses on the activities of working group 1 (WG1) on the ‘Urban Wind Field’. Due to the large size of the roughness elements, the urban boundary layer has a more structured layering than boundary layers over smoother surfaces. In particular, the surface layer, i.e. the ‘lowest‘ atmospheric layer over relatively smooth surfaces is split up into the inertial sublayer and the roughness sublayer and the latter contains the so-called canopy layer. This vertical structure has to be taken into account when attempting to estimate input variables for urban dispersion modeling purposes from nearby observations (e.g., from an airport). WG1 has identified five areas of interest, namely i) the roughness sublayer, ii) the (remaining part of the) urban boundary layer, iii) the rural – urban transition, iv) the intra-urban spatial inhomogeneity and v) the design of urban meteorological networks. For each of these ‘tasks‘, the existing knowledge is being reviewed and a hypothesis is formulated how to use this knowledge in order to estimate the wind field in an urban boundary layer. Also, a collection of data sets is identified for testing the above conjectures. Clearly, these hypotheses and the presented examples based on the existing data sets by no means reflect final and approved results but rather the present status of an ongoing work. Special emphasis will therefore also be given to the gaps in our knowledge and the respective needs for further research (and data).