Calculation of the impacts of aerosols on cloud microphysical properties by combining ground- and space-based measurements

Abstract. The effect of aerosols on cloud properties remains poorly constrained, in part because ground-based measurements are highly local while space-based retrievals are spatially imprecise. Here, we show how the two viewpoints can be combined using colocated surface aerosol measurements and thermodynamic profiling from the peri-urban ATOLL (ATmospheric Observatory in LiLLe) site and geostationary-satellite cloud microphysical retrievals from the SEVIRI instrument. Focusing on low-level stratiform clouds that formed under thermodynamically stable conditions, we relate cloud properties to aerosol light scattering as a proxy for cloud condensation nucleus concentrations for two cloud liquid water path bins of 20–100 and 100–200 g m^–2. Relative changes of cloud droplet number concentrations and effective radii are compared to relative changes in aerosol light scattering coefficient to find respective susceptibilities. The susceptibility of the cloud droplet number concentration to the aerosol scattering coefficient (S_n), also called nucleation efficiency, is retrieved around 0.29 for LWP (Liquid Water Path, from 20 to 100 g m^-2) and around 0.30 for higher LWP (between 100 to 200 g m^-2). For the same LWP ranges, the susceptibility of the effective radii to the aerosol burden (S_re) is around 0.08 and 0.07, respectively. These values are consistent with, although on the lower side of, prior studies of continental stratus. Uncertainties in this study are dominated by a small sample size and satellite retrieval biases. However, the approach is readily extensible to other ground-based sites measuring boundary layer aerosol concentrations pointing towards a method for better constraining susceptibility calculations globally.