Siting and Exposure of Meteorological Instruments at Urban Sites
There is a growing need for meteorological data in urban areas in support of air pollution research and management, but measurement poses substantial challenges. Most densely-developed sites make it impossible to conform to the standard WMO Guidelines for site selection and instrument exposure (WMO, 1996) due to obstruction of airflow and radiation exchange by buildings and trees, unnatural surface cover and waste heat and water vapour from human activities. New guidelines (Oke, 2004) to assist in this task form the basis of the first part of this paper. Here emphasis is on those variables of greatest use in air pollution applications. Valid and repeatable results can be obtained despite the heterogeneity of cities, but it requires careful attention to principles and concepts specific to urban areas. Guidelines must be applied intelligently and flexibly, rigid ‘rules’ have little utility. It is necessary to consider exposures over non-standard surfaces at non-standard heights, splitting observations between more than one location, or being closer to buildings or anthropogenic heat and vapour sources than is normal WMO recommended practice.
KeywordsStreet Canyon Urban Site Wind Profile Urban Station Internal Boundary Layer
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