Abstract
Concentration fluctuations in a dispersing plume are investigated theoretically for situations in which the instantaneous plume is much narrower than the ensemble mean plume (defined here, somewhat imprecisely, as an average over an ensemble of realizations in which the large-scale meteorology is fixed but the boundary layer turbulence varies—the imprecision is a consequence of the difficulty of clearly distinguishing turbulence and changes in meteorology). It is shown that in such situations there is a range of scales that lies in the inertial subrange and that also contribute to plume meandering. Over such scales, the theory implies that a power-law regime should occur in the concentration spectrum, with the spectrum being proportional to wavenumber (or frequency) to the power of −1/3. Experimental results showing evidence for the regime are presented, and the regime is related to the ideas of F. Pasquill.
Corresponding author address: Dr. David J. Thomson, Meteorological Office, Room 171, London Road, Bracknell, Berkshire RG12 2SZ, United Kingdom.E-mail: djthomsonmeto.gov.uk
