The evolution of droplet spectra by condensation and coalescence in cumulus clouds

✍ Scribed by P. R. Jonas; B. J. Mason

• Publisher: John Wiley and Sons
• Year: 1974
• Tongue: English
• Weight: 603 KB
• Volume: 100
• Category: Article
• ISSN: 0035-9009
• DOI: 10.1002/qj.49710042503

✦ Synopsis

Abstract

The paper describes calculations of the development of droplet‐size spectra in cumulus clouds under the combined effects of condensation and coalescence. It is demonstrated that the concentration of condensation nuclei is a more important factor in controlling the onset of precipitation than is the updraught, at least for small clouds. It is shown that condensation can indirectly affect the growth rate of droplets larger than 25 μm radius by enhancing the growth of the smaller droplets which are then captured more efficiently by the larger ones. The overall result is to produce more rapid distortion of the droplet spectrum and more rapid growth of the largest drops than would occur by condensation and coalescence acting separately to produce an apparent barrier to the growth of droplets between 20 μm and 30 μm in radius. The onset of precipitation in continental clouds containing a high nucleus concentration depends rather critically on the values used for the collection efficiencies of droplets of radius < 40 μm and may be considerably accelerated if the collection efficiencies are increased by small‐scale atmospheric turbulence.