A Ternary Framework for Marine Stratocumulus Morphology and Cloud Susceptibility

We introduce a new framework for defining marine stratocumulus cloud morphologies using a ternary diagram. The method is applied to one year of satellite observations of stratocumulus clouds and reveals the frequency of occurrence of different morphologies across the ternary space. Large-eddy simulations complement the satellite analysis and show that cloud evolution tends to follow preferred pathways across the ternary space, explaining why observations are concentrated within a limited range of morphologies. We further investigate the susceptibility of cloud liquid water path (LWP) and cloud albedo to variations in droplet number concentration, conditioned on cloud morphology. For the most frequently observed morphologies, LWP and cloud albedo susceptibilities largely offset each other, resulting in a net in-cloud albedo response close to zero. These findings have important implications for marine cloud brightening, whose effectiveness should be evaluated in a morphology-dependent framework, as well as for estimates of cloud radiative forcing due to aerosol–cloud interactions, which should be based on morphology-weighted averages.