Horizontal Variability in 10 m Wind Velocities as Observed at Two Prairie Sites Separated by a Distance of 7.5 km

Abstract

It is important to assess the representativeness of mesoscale wind data because most short range pollution models assume that wind velocity will remain constant over distances in the order of 10 km. Previous observational studies have shown that average hourly mesoscale differences in wind directions and speeds might be typically about 25 degrees and 1 m s?1. Initial results of this study using all available data, tended to agree with the above findings. Further analyses, however, were performed for periods to which most pollution models are restricted. These periods are usually characterized by the absence of mesoscale wind phenomena and terrain effects associated with katabatic winds. Hourly wind direction differences for these periods were found to be typically only about 10 degrees regardless of atmospheric stability. Wind speed differences were still typically about 1 m s?1. Differences of both wind speed and direction were normally distributed, suggesting that horizontal mesoscale wind velocity differences occur randomly. For this reason it may be impractical to attempt the development of short-range plume dispersion models that physically account for horizontal inhomogeneities.