Disentangling Driver Interactions Governing Cloud Radiative Effect in Stratocumulus over the DOE ARM ENA site

At any time, boundary layer stratocumulus clouds cover much of the earth, modulating heat, moisture, and radiative fluxes at boundary layer top. As important as they are, they remain one of the least understood components of the earth system and are responsible for much of the uncertainty in climate simulations. This is partially due to aerosol-cloud interactions, which can profoundly impact cloud dynamics and how clouds interact with radiation. Aerosols can brighten clouds and increase their lifetime, though feedbacks within the system often buffer these effects.

Because so many interactions govern radiative effect of stratocumulus, we use a fully nonlinear causal framework which can disentangle interactions and implicate sources of missing physics. The method identifies processes such as activation, condensation, collection, and entrainment. Comparing drizzling stratocumulus with non-drizzling stratocumulus, many processes, such as liquid water content conservation, act similarly, but the tendency to large-scale liquid water path equilibrium manifests vastly differently, related to the high importance of collection in drizzling clouds. Furthermore, when a known driver, e.g. drizzle, is purposely excluded, the framework accurately identifies it as a missing driver.

In this presentation we will discuss these effects in detail, highlighting the multiple pathways from aerosols to cloud radiative effect, mediated by meteorology and micro-physics. Emphasis will be on how these pathways differ between drizzling and non-drizzling clouds. We will also discuss the completeness of our causal study and how the causal framework helps us in identifying missing variables and processes.