An Investigation of the Representativeness of Wind Measurements Made in a Complex Terrain Region of Southern Virginia

Many air quality and dispersion models require representative meteorological data as input to produce accurate results. Data used as meteorological input for air quality and dispersion models should reflect the actual conditions over the entire modeled region. Site selection for representative meteorological measurements in certain landscapes (i.e. urban, land/sea interface, complex terrain) is not always straightforward, and requires further investigation. In particular, meteorological variables can be highly affected by the underlying topography in complex terrain. Complex terrain can cause certain meteorological variables, such as wind speed and wind direction, to vary over small spatial scales. These variations are of particular concern during stable conditions, when the topographic influence over the local winds is the strongest. A proposed mining and milling operation in Southern Virginia has motivated a study about the representativeness of wind measurements made at a single baseline site in the region. The objective of this study is to determine the representativeness of wind measurements made at this site. To fulfill this objective, four 10-m meteorological towers were set up surrounding a 10-m meteorological tower at the baseline site. Data collected in a 17-month period were used in thorough statistical and wind rose analyses to qualitatively and quantitatively investigate the meteorological factors affecting the representativeness of the baseline tower. The factors that were analyzed include stability, synoptic wind speed, and synoptic wind direction. The results from these analyses show that the representativeness of the baseline tower is reduced during stable conditions in the presence of topographically induced flows. It was found that topographically induced drainage flows exist to some extent at all the sites from the northwest, but are most pronounced at the baseline site. These flows impact the representativeness of the baseline site most under stable and synoptically quiescent conditions, irrespective of synoptic wind direction. Intensive field campaigns were conducted at the baseline site and one additional site to investigate the temporal and spatial characteristics of these topographically induced flows over the region. Results from the field campaigns indicate that the onset of drainage flows occurs earlier in the night at the baseline site compared to the additional site when synoptic flows are relatively weak. This study will contribute to the development of better guidelines for collecting representative wind measurements in areas of moderately complex terrain.