A Near-Global Diagnostic Study of Apparent Morning Aerosol Effects on Afternoon Clouds, Precipitation, and Radiation

The presentation will focus on the results of a “high volume” study to diagnose relationships between aerosol and cloud properties or cloud-affected quantities (precipitation, radiation). Due to its near-global and multi-year nature, the analysis is based on gridded (“Level-3”) daily data. It uses as framework a systematic cloud classification in terms of “cloud regimes” (CRs, derived by clustering cloud top pressure – cloud optical thickness joint histograms from MODIS). Aerosol optical depth (AOD) variations come either from MODIS or MERRA-2 re-analysis and are defined relative to a region’s local seasonal climatology. A centerpiece of our analysis approach is the exploitation of the 3-hour difference between Terra (morning) and Aqua (afternoon) overpasses. Specifically, our presentation will assess whether Aerosol-Cloud-Precipitation-Radiation interactions (ACPRI) can be diagnosed by investigating: (a) The dependence on morning AOD percentile of afternoon cloud-affected quantities composited by afternoon or morning CRs; and (b) whether clouds represented by ensemble cloud top pressure – cloud optical thickness joint histograms appear sufficiently distinct under low and high AOD conditions when preceded by specific CRs. We will explain how our approach addresses long-standing aspects of the ACPRI problem such as the optimal ways to decompose the problem by cloud class, the prevalence and detectability of 1st/2nd aerosol indirect effects and invigoration, and the effectiveness of aerosol changes in inducing cloud modification at different segments of the AOD population.