Alongwind Dispersion—A Simple Similarity Formula Compared with Observations at 11 Field Sites and in One Wind Tunnel

Abstract

Observations of alongwind dispersion of clouds were collected from 11 field 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 σt, the standard deviation of the concentration time series. The observed σts range from 0.3 to 9000 s. The concentration time series observations also allow the travel time t from source to receptor to be estimated, from which the cloud advective speed ue can be determined. Observed ts range from 2 to 40?000 s, and observed ues range from 0.5 to 16 m s?1. The alongwind dispersion coefficient σx is then calculated from ueσt. The resulting σt and σx observations support the similarity relations σt = 0.1t and σx = 2u?t, where u? is friction velocity. About 50% of the observations are within a factor of 2 of these similarity relations.