Explorations of Processes That Affect Cloud Susceptibility to Aerosol in Global Models (Invited Presentation)

Aerosol cloud interactions continue to be a source of large uncertainties in estimates of historical responses of the earth system to anthropogenic forcing agents. Recent studies e.g. (Malavelle et al, 2017) provide hints that some models are very sensitive to changing aerosols, while others are much less susceptible (and appear to agree more closely to observations). Those results are particularly intriguing because models with widely disparate responses appear to be using very similar treatments of cloud microphysics. We explore choices made by global modelers that can contribute to this strong sensitivity, including cloud microphysics, aerosol physics and chemistry, model resolution, implementation details, and choices influencing the natural background aerosol field that modulate cloud responses to aerosol perturbations.