Coupling between Cloud and Land Surface Modulated Aerosol-Cloud Interactions

Aerosol-cloud interactions (ACI) are vital for regulating Earth's climate by influencing energy and water cycles. Yet, the magnitude of these impacts is still fraught with large uncertainties, especially systematic discrepancies between observed and modeled ACI estimates. A major source of bias is identified in this study in the determination of aerosols interacting with clouds, as conventional measurements are made from the surface or space, neither reflecting the aerosol at the cloud level unless the cloud is coupled with the surface. This study introduces a novel approach of determining the ACI by accounting for the state of cloud-surface coupling, that has been missing in previous studies, incurring significant biases. We combine field observations, satellite data, and model simulations to reveal a drastic alteration in both aerosol vertical transport and the magnitude of ACI caused by cloud-surface coupling. In coupled states, aerosols mix thoroughly with clouds, enhancing cloud droplet number concentration and brightness, leading to stronger ACI than previously estimated. On the other hand, in decoupled states, the aerosol concentrations decrease significantly with height, yielding weaker ACI with substantial uncertainties. Our findings underscore the impact of cloud-surface coupling on ACI, advancing our ability to constrain aerosol indirect radiative forcing and may help refine climate change projections.