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Preliminary studies of the distribution of particles at medium range from a ground‐level point source
Author(s) -
Pasquill F.
Publication year - 1955
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49708135024
Subject(s) - environmental science , meteorology , range (aeronautics) , atmospheric sciences , ground level , inversion (geology) , wind direction , wind speed , geology , geodesy , physics , materials science , seismology , composite material , tectonics , architectural engineering , ground floor , engineering
As a basis for planning a comprehensive study of the diffusion of airborne material over distances up to 100 mi a small number of exploratory experiments was carried out during February‐April 1955, using as a tracer a fluorescent pigment similar to that described by Braham et al. in Trans. Amer. Geophys. Un. , December 1952. Samples were taken at distances up to 40 mi downwind of a ground‐level source and at heights up to 4,000 ft, using an impactor with a receiving surface in the form of a drum, the instrument being carried across the cloud in a Land‐Rover and a Hastings aircraft of the Meteorological Office Research Flight based at R.A.E., Farnborough. The direction and speed of travel of the clouds were on the average closely in accordance with the measured vector mean wind over the first 2,000 or 3,000 ft, individual deviations therefrom being ± 5° in direction and ± 4 mi hr −1 in speed. The conditions were mainly moderately unstable in the lower layers with overhead inversions at heights ranging from 2,000 to 7,500 ft. Effective extreme cloud widths ranged from about 40° (angle subtended at source) at 5 mi to about 20° at 40 mi. Vertical diffusion in the layer between the ground and the inversion appeared to be an order of magnitude more rapid than in the lower atmosphere in neutral conditions of stability. No decisive evidence was found as regards the effect of an overhead inversion in limiting the extent of vertical diffusion. The difficulties encountered in obtaining and interpreting the distribution downwind of a source of short duration emphasize that it would be more profitable to use a longer duration source and to carry out the sampling operations away from the leading and trailing edges of the cloud.