Simulating aerosol lifecycle impacts on the subtropical stratocumulus-to-cumulus transition using large eddy simulations

Abstract

Low marine clouds are the most widespread clouds on Earth, and they significantly affect the Earth's radiation balance by strongly reflecting sunlight (Wood, 2012). They are also a main source of uncertainty in cloud feedback across global climate models (Bony & Dufresne, 2005;IPCC, 2013;Zelinka et al., 2017), largely due to the necessary use of physics parameterizations that represent subgrid processes in those models. Stratocumulus (Sc) clouds are the predominant type of low marine cloud over the eastern subtropical oceans where the shallow and often well-mixed marine boundary layer (MBL) lies between cold surface ocean water and a strong capping inversion induced by the strong subsidence of warm and dry air aloft (Bretherton et al., 2004;Wood, 2012).As Sc clouds are transported westward and equatorward by Trade winds, the warmer ocean water enhances surface latent heat fluxes, making the MBL deeper and promoting a decoupled state, with shallow cumulus (Cu) clouds rising into an Sc layer below the inversion. Enhanced buoyancy within the Sc layer, penetrative entrainment by Cu updrafts, and weakened subsidence above the inversion cause stronger entrainment of dry air from the free troposphere (FT) and the eventual dissipation of the Sc cloud (