Extended Abstract (2.4M)4.5
Atmospheric turbulence and diffusion estimates derived from plume image analysis
Carmen J. Nappo, NOAA/ARL/ATDD, Oak Ridge, TN; and D. Miller and A. L. Hiscox
Gifford's 1959 paper on the use of smoke plumes as quantitative air pollution indices was one of the first to exploit Roberts' 1923 opacity theorem, i.e., the visible edge of a smoke plume represents a constant integrated-line-of-sight concentration of light scattering particles. Gifford assumed a normal cross-section concentration distribution of scattering particles and used the opacity theorem to define the relative concentration along the visible edge of a time-averaged smoke plume. Because the shape of a smoke plume is determined by the downwind variations of cross-wind dispersion parameters, Gifford reasoned that one can ‘invert' the problem and estimate the dispersion parameters and their downwind variations using the observed plume shape. Since then, this technique has been extended to estimate turbulence parameters using time-averaged and instantaneous photographs of smoke plumes. Most recently, the method has been applied to LIDAR scans of smoke plumes in the nighttime boundary layer when photography is not possible or when the concentrations of light scatterers in the daytime boundary layer are too low to visibly show a plume. In this paper, the details of the smoke-plume analysis are reviewed, and some results form the Joint Observational Research on Nocturnal Atmospheric Dispersion of Aerosols (JORNADA) program are presented. Specifically, LIDAR images of a smoke plume released about 11 m AGL were used to measure dispersion parameters in the stable boundary layer. Time-averaged and near-instantaneous dispersion estimates about 60 m downwind of the plume's source were calculated. Dispersion parameters had a median value of about 2.3 m with values ranging between 0.6 and 5.4 m. Of particular interest, was the observation of increased dispersion during a period of intense gravity wave activity. These observations could not have been made using time-averaged sampling at the ground surface.
Session 4, Frank Gifford Memorial Session
Monday, 21 January 2008, 4:00 PM-5:30 PM, 220
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