Novel insights into aerosol-cloud interactions enabled by analysing the temporal evolution of strong anthropogenic cloud perturbations

Anthropogenic aerosol particles affect clouds by serving as cloud condensation nuclei, thus significantly influencing Earth’s energy balance. The magnitude of aerosol-induced changes in cloud properties is still uncertain. This is primarily due to the meteorological covariability between aerosols and clouds, which hinders inferring causal relationships. Industrial air pollution sources serve as natural experiments to study strong anthropogenic cloud perturbations (Toll et al. 2019 Nature https://doi.org/10.1038/s41586-019-1423-9) and allow us to infer causal relationships between aerosols and clouds.

 

We use geostationary satellite observations to study the temporal evolution of polluted clouds. Polluted clouds are usually thinner than nearby unpolluted clouds. But in some cases, the polluted clouds grow much thicker in the afternoon than the nearby unpolluted clouds. We find that continental polluted cloud tracks are relatively long-lived, with a median lifetime of 18 hours. Moreover, there are many cases where polluted cloud tracks are visible for multiple consecutive days. This means polluted cloud tracks live long enough for clouds to fully adjust to aerosol-increased cloud droplet numbers. Future work is needed to combine geostationary and polar orbiting satellite observations of polluted cloud tracks to develop stronger observational constraints for aerosol-cloud interactions.