Alongwind dispersion - A simple similarity formula compared with observations at 11 field sites and in one wind tunnel

Observations of alongwind dispersion of clouds were collected from 11 held sites and from one wind tunnel and were used to test simple similarity relations. Because most of the observations consist of concentration time series from fixed monitors, the basic observed variable is sigma (t), the standard deviation of the concentration time series. The observed sigma (t)s range from 0.3 to 9000 s. The concentration rime series observations also allow the travel time t from source to receptor to be estimated, from which the cloud advective speed u(e) can be determined. Observed is range from 2 to 40 000 s, and observed u(e)s range from 0.5 to 16 tn s(-1). The alongwind dispersion coefficient sigma (x) is then calculated from u(e)sigma (t). The resulting sigma (t) and sigma (x) observations support the similarity relations sigma (t) = 0.1t and sigma (x) = 2u(*)t, where u(*) is friction velocity. About 50% of the observations are within a factor of 2 of these similarity relations.