Sensitivity of Stratocumulus–Cumulus Transitions in a Cloudy Energy Balance Model

Abstract Stratocumulus (Sc) clouds have high impact on the climate system because of their strong cooling effect (albedo). In the subtropical oceans they naturally break up into cumulus (Cu) as environmental conditions change, a phenomenon called Stratocumulus–Cumulus Transition (SCT). SCT results in significant loss of cooling due to reduction in cloud cover, and it could be triggered more frequently under future environmental conditions. To better understand the physical processes and environmental conditions influencing most this transition, we develop a conceptual mixed layer model with dynamic cloudiness and sea surface temperature (SST). In this model Sc and Cu states are two alternative attractors of the dynamics. We tested various different parameterizations, and in most configurations the model broadly reproduces observed variability in cloud fraction, SST, heat fluxes, and moisture. In this isolated system we robustly show that transitions between Sc and Cu are most sensitive to changes in circulation. In climate change scenarios we show that SCT is enhanced due to direct radiative effects of increasing CO 2 and due to weakening subtropical subsidence deepening the boundary layer. We also highlight the differences between linear and nonlinear response of clouds to weakening subsidence. This positive feedback of climate‐change‐amplified SCT is a potentially high impact effect that warrants further study. Our work is accompanied by a flexible and easy‐to‐use codebase that allows performing further studies with similar or derived conceptual frameworks based on the DynamicalSystems.jl software library.