1501 OCTOBER 2002 AMERICAN METEOROLOGICAL SOCIETY | T he workshop on Urban Boundary Layer Param- eterizations was organized as an activity within COST 715 (Meteorology Applied to Urban Air Pollution Problems) by Working Groups 1 and 2 of this COST action. COST (an acronym translated from the French for European Cooperation in the Field of Scientific and Technical Research) is a European framework for the coordination of nationally funded research within Europe. A “COST action” operates within a bottom-up structure that is administered by individual scientists through working groups and a so-called management committee. This particular workshop was held in Zurich, Switzerland, on 24– 25 May 2001 and consisted of a series of scientific pre- sentations and an extensive discussion by all the par- ticipants (about 50 people from 18 countries). Extended abstracts of the individual presentations will be published as a proceedings volume by the Euro- pean Commission. They can be downloaded from the Web site of Working Group 1 (www.iac.ethz.ch/en/ research/cost715/cost715_2.html). In this contribu- tion a short outline of each presentation is given and the discussion is summarized. OVERVIEW OF THE PRESENTATIONS. S. E. Belcher (University of Reading) presented a new model for the flow in the lowest part of the urban boundary layer, that is, the roughness sublayer. The approach does not resolve individual buildings but rather treats the spatially averaged flow field with all its consequences. Scaling considerations were pre- sented as well as an approach for the turbulence clo- sure (mixing length approach). The model was shown to favorably correspond to available datasets (mainly from regular array wind tunnel or “semi-full-scale” physical modeling). An overview of various modeling approaches for urban applications in numerical models was given by R. Bornstein (San Jose State University). In broad terms, three types of approaches can be distinguished. • the “traditional” approach (termed the flat sand- box type by the author), in which only parameter COST 715 WORKSHOP ON URBAN BOUNDARY LAYER PARAMETERIZATIONS BY MATHIAS W. ROTACH, BERNHARD FISHER, AND MARTIN PIRINGER State-of-the-art parameterizations of the urban atmospheric boundary layer applied to air pollution dispersion modeling were reviewed by leading experts. Current theories with modifications just survive critical appraisal. AFFILIATIONS: ROTACH—Swiss Federal Institute of Technology, Institute for Atmospheric and Climate Science, Zurich, Switzerland; FISHER—Environment Agency, London, United Kingdom; PIERINGER— Central Institute for Meteorology and Geodynamcis, Vienna, Austria CORRESPONDING AUTHOR: Mathias Rotach, Institute for Atmospheric and Climate Science ETH, Swiss Federal Institute of Technology, Winterhurerstrasse 190, Zurich CH-8057, Switzerland E-mail: rotach@geo.umnw.ethz.ch DOI: 10.1175/BAMS-83-10-1501 In final form 20 May 2002 ©2002 American Meteorological Society