Mesoscale Processes of Trade-Cumulus Clouds - A Review Framework and Diagnostics for Model Benchmarking

Trade-wind shallow convection, a major source of uncertainty in cloud-feedback estimates, exhibits pronounced meso-scale (O(10-100 km)) variability, with organization patterns that depart strongly from the canonical “popcorn” cumuli and has thus gained the attention of many investigations in the past decade. We review these advances and present them in a unifying framework which highlights how mesoscale heterogeneities emerge from interactions between internal processes and external forcings. The internal processes include meso-scale circulations, cold-pools and convection-scale elements such as thermals, whereas external forcings are conventional large-scale cloud controlling factors (CCFs) such as sea-surface temperature gradients, wind speed and shear, the stability and humidity at inversion levels, etc. The interactions between these internal processes and external forcings result in a ubiquitous presence of mesoscale organized systems of shallow cumuli which crucially regulate cloud fraction, radiative effects and precipitation. The process-studies over the years allows provides diagnostic means to validate the representation of these processes in models. From literature, we thus also collate diagnostics to be used as a benchmark dataset on meso-scale processes and their large-scale imprint as reference for the validation of simulations, development of new parameterizations and establishment of new constrains. The benchmark dataset is based on high-resolution simulations and observations and contains products and software code to facilitate the inter-comparison with additional sources.