The effect of polluted and continental airmasses on stratocumulus cloud

Publisher Summary This chapter uses the data collected by the Met Research Flight's C-130 aircraft during flights around the UK and Europe in air masses with various levels of pollution in order to extend the parameterization presented by Martin, referred to as MJS94. This parameterization hinges on the use of the effective radius, a measure of the ratio of absorption to scattering for an ensemble of cloud droplets. Bulk aerosol and cloud droplet measurements and the droplet size distribution derived quantity κ show that a parameterization, treated as an extension to the MJS94 parameterization, for the effective radius of cloud droplets within highly polluted air masses, including those over land surfaces, is possible. Such a parameterization can be envisaged as the evolution of an air mass away from the source region (over land) over the sea as the aerosol dilutes, sediments out, and is processed. The processing of aerosol by cloud could also be parameterized—in terms of the nucleation, accumulation, and coarse mode mass or number concentration, as a function of distance or time. Changes in number concentration, within the accumulation mode especially, has implications for the direct scattering of solar radiation (direct forcing effect) and CCN characteristics (indirect forcing effect).