Anthropogenic aerosol effects on convective cloud microphysical properties in southern Sweden

Abstract

In this study, we look for anthropogenic aerosol effects in southern Scandinavia’s clouds under the influence of moderate levels of pollution and relatively weak dynamic forcing. This was done by comparing surface aerosol measurements with convective cloud microphysical profiles produced from satellite image analyses. The results show that the clouds associated with the anthropogenic-affected air with high PM_0.5, had to acquire a vertical development of ∼3.5 km before forming precipitation-sized particles, compared to less than 1 km for the clouds associated with low PM_0.5 air-masses.

Additionally, a comparison of profiles with precipitation was done with regard to different potentially important parameters. For precipitating clouds the variability of the cloud thickness needed to produce the precipitation (Δh₁₄) is directly related to PM_0.5 concentrations, even without considering atmospheric stability, the specific aerosol size distribution or the aerosols’ chemical composition. Each additional 1 μg m−3 of PM_0.5 was found to increase Δh₁₄ by ∼200–250 m.

Our conclusion is that it is indeed possible to detect the effects of anthropogenic aerosol on the convective clouds in southern Scandinavia despite modest aerosol masses. It also emphasizes the importance of including aerosol processes in climate-radiation models and in numerical weather prediction models.