Geofisica pura e applicata

, Volume 43, Issue 1, pp 227–242 | Cite as

The nuclei of natural cloud formation part I: The chemical diffusion method and its application to atmospheric nuclei

  • S. Twomey


Condensation nuclei which grow into droplets in natural clouds constitute only a small fraction of the total population of nuclei, since they must be activated at low supersaturations (<1%). Such nuclei cannot readily be measured by the usual expansion methods. A chemical diffusion method is described in which water vapour and HCl vapour diffuse between a water surface and an aqueous HCl solution; this produces the continuous small supersaturations required to study these «cloud nuclei». Nucleus numbers are obtained photographically. Results of observations made by this method during the period April–August 1958 are presented and discussed; they suggest that the main source of cloud nuclei is the dry land surface.


Water Vapour Land Surface Supersaturation Expansion Method Formation Part 
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Copyright information

© Istituto Geofisico Italiano 1959

Authors and Affiliations

  • S. Twomey
    • 1
  1. 1.C.S.I.R.O., Division of RadiophysicsUniversity GroundsSydneyAustralia

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