Fit-for-purpose assessment of satellite aerosol and cloud datasets for constraining and monitor aerosol–cloud interactions

Abstract. Aerosol-cloud interactions (ACI) remain one of the dominant sources of uncertainty in estimates of anthropogenic effective radiative forcing. Robust observational constraints on these processes require satellite datasets that are not only physically consistent but also demonstrably fit for the intended scientific purpose. Within the framework of the "Satellite observations to improve our understanding of aerosol–cloud interactions" (SATACI) project, we perform a comprehensive fit-for-purpose (F4P) assessment of existing satellite aerosol and cloud datasets used to (i) quantify aerosol indirect effects on liquid and mixed-phase clouds and (ii) support the feasibility study of a novel aerosol–cloud climate indicator. For each application, scientific and technical requirements are defined in terms of variables, spatial and temporal resolution, co-location capability, validation evidence, and the availability of uncertainty information. Candidate datasets from geostationary and polar-orbiting satellites are evaluated against these criteria, including datasets resulting from the ESA Climate Change Initiative and Copernicus Climate Change Service. Overall, the study highlights the importance of application-specific dataset evaluation and emphasises the complementary roles of geostationary and polar-orbiting satellite observations. While geostationary sensors provide new opportunities to investigate the temporal evolution of aerosol–cloud systems, polar-orbiting climate data records remain essential for long-term monitoring and climate indicator development. Together, these observations provide a robust basis for advancing satellite-based constraints on aerosol–cloud interactions.