upper ‘cut-off frequency which decreases as the time of travel of the particles increases, i.e. as we go further from the source. Thus the dispersion a t large distances from the source is determined mainly by the larger eddies in the flow and the smaller, high-frequency eddies do not contribute to the permanent lateral displacement of a particle although they are, of course, still present in the tur- bulence.

Although we have considered only a point source of pollution here, the extension of these ideas to larger, more complex sources presents no conceptual difficulties. In practice, of course, it is not possible to use this simple method as a means of predicting dispersion, as too many important meteorological factors have been omitted (the shear of the wind in the boundary layer, and the effect of static stability on vertical dispersion, among others). However, this simple model does show how the real problem must be tackled, and its essentials are incorpora- ted in one of the practical methods of predicting atmospheric dispersion (see e.g. Pasquill 1962).

This article was intended to provide only an introduction to some of the simpler aspects of the description of turbulent flow, without looking at its dynamics. Hopefully it has also indicated how information about the structure of turbulence can assist in solving some of the environmental problems with which meteorologists must be concerned. Unfortunately, any further examination of turbulence must involve more mathematics, but interested readers may like to sample the references given below, none of which is too demanding mathemat- ically.

ACKNOWLEDGEMENTS

I should like to thank Mrs K. Daykin for her preparation of the diagrams, Dr M. A. Pedder and Mr G. K. Thwaites for assistance in computing spectra, and Dr J. R . Milford for his helpful comments on the manuscript.

REFERENCES

OWEN, P. R.

PASQUILL, F. 1962 Atmospheric diffusion, Van Nostrand SUTTON, 0. G. 1949 Atmospheric turbulence, Methuen

1971 Buildings in the wind (Symons Memorial Lecture). Quart. J . R. Met. Sac., 97, pp. 396413

ROYAL METEOROLOGICAL SOCIETY SYMONS MEMORIAL GOLD MEDAL

HE 1977 award of the Symons Memorial Gold Medal was made to T Professor K. Ya. Kondratyev (Institute of Physics, Leningrad University, U.S.S.R.). The award was made to Professor Kondratyev for his fundamental contributions in the fields of solar and atmospheric radiation. In the photo- graph opposite, Professor Kondratyev (left), Professor E. P. Borisenkov (Director, Main Geophysical Observatory, Leningrad, U.S.S.R.), Mrs Kondratyev and Professor R. Hide (right) (Past President of the Royal Meteorological Society) are seen leaving the Main Geophysical Observatory after the Syinons Medal Presentation Ceremony there on 23 June 1978.

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ALPINE MORNING

Photograph by W. U . L. Weimann Alpine morning at Morgins, Val de Morgins, Switzerland (1250 m)

SYMONS MEDALLIST, 1977

Professor K. Ya. Kondratyev (left) after the ,Symons Veda1 Presentation Ceremony in

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Leningrad on 23 June 1978. See text opposite for details