Influence of Rainfall on the Seasonal Variations of Cloud Condensation Nuclei Concentrations in a Sub-Equatorial Climate

Abstract

Systematic measurements of cloud condensation nuclei (CCN) concentration have been carried out in the Abidjan area from December 1977 to June 1978, at 0700 local time (corresponding to a daily maximum). In that period of the year, from the main dry season to the main rainy season, a general decrease of CCN concentrations has been noted. This decrease is more marked for the more active CCN. In May and June 1978, during the continuous monsoon rains, the concentrations substantially increased, this effect being more important for the fraction of the less active CCN. Nuclei of continental origin accompanying dust haze in December 1977 were progressively eliminated from the atmosphere by dry or wet deposition. They wore replaced by smaller nuclei. originating in vegetation, the production of which was increased by the continuous monsoon rains.