Global variation of column droplet concentration in low-level clouds



Cloud droplet concentration is a very important parameter in model studies. However, no global observation is available because it is hard to retrieve by current satellite remote sensing techniques. This study introduces another parameter, column droplet concentration, which can be retrieved by satellite data and used in models. The column droplet concentration (Nc) is the product of cloud geometrical thickness and droplet volume number concentration. This paper presents a method and the results of retrieving column droplet concentration for low-level clouds. The first near-global survey (50°S to 50°N) of Nc reveals more clearly the effect of aerosol concentration variations on clouds. The survey shows the expected increase of column droplet concentrations between ocean and continental clouds and in tropical areas during dry seasons where biomass burning is prevalent. Therefore, column droplet concentration is demonstrated as a good indication of available CCN populations in certain areas.