Stratocumulus-cumulus transitions in present and future climates
Stratocumulus clouds occurring over eastern subtropical ocean basins dominate climatological cloudiness at low latitudes and are important for Earth’s global radiative energy budget. Further west, there is an observed transition to scattered cumulus cloud cover, the so-called stratocumulus-cumulus transition (SCT). To explore the mechanisms driving the SCT, I will present an extension of the traditional bulk boundary layer model for stratocumulus-topped boundary layers that explicitly considers cloud decoupling from the surface and subsequent cloud fraction reduction. I will then use this model to consider cloud decoupling and breakup in response to increased CO2 concentrations in an idealized two-column framework. Finally, I embed this representation of decoupling-induced cloud breakup in CESM2 to explore the direct effect of CO2 on low cloud cover while retaining a realistic representation of the large-scale circulation and thermodynamic state of the free-troposphere. I will show preliminary results from these experiments and discuss the implications of these results for nonlinear cloud feedbacks and direct cloud adjustments.
