Aerosol Vertical Distribution Influences the Cloud-Top Entrainment of Marine Stratocumulus Clouds over the Southeast Atlantic

This study utilizes aircraft observational data from the ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) campaign to investigate how aerosol vertical structure influences the cloud microphysics of marine stratocumulus by modulating the cloud-top entrainment. It is found that the existence of an above-cloud aerosol layer increases the cloud droplet number concentration and effective radius near cloud top. This indicates aerosols may be entrained into clouds and activated as cloud droplets. The cloud-top entrainment is most evident when above-cloud aerosol is separated from cloud tops. Under such profiles cloud radiative flux is reduced, enhancing the cloud-top cooling, inhibiting inversion, increasing the wind sheer and turbulence. In contrast, an above-cloud aerosol layer in contact with the clouds absorbs solar radiation, warms the cloud top, and introduces opposite effects. This work improves our understanding of aerosol-cloud interactions and helps reducing uncertainties in climate models.