Measurements of condensation nuclei over the North Atlantic

Abstract Measurements of the total concentration of condensation nuclei and of the concentration and size distribution of large sea‐salt nuclei have been made on board an Ocean Weather Ship in the North Atlantic over a period of three weeks. Total nucleus counts varied between 77/cm 3 and 2,460/cm 3 , the numbers decreasing with increase in the intensity of vertical mixing as indicated by cloud type. The concentration of large nuclei (mass > 10 −11 g) was found to increase markedly with wind speed and wave height, but no corresponding increase was found for the total nucleus population. An analysis of the visibility observations at the Ocean Weather Ship Stations ‘Item’ and ‘Jig’ shows that the opacity for a given humidity increases with wind speed and wave height and that this increase can be accounted for by the observed increase in the concentration of large nuclei. Consequently if the rate of production of small nuclei at the sea surface increases with wind speed, such increase (for wind speeds up to 18 m/sec) does not materially affect the total nucleus population a few metres above the surface.