Modeled aerosol-cloud indirect effects and processes based on an observed partially glaciated marine deep convective cloud case

Abstract

A tropical maritime case of deep convective clouds was studied using a state-of-the-art aerosol-cloud model in order to evaluate the microphysical mechanisms of aerosol indirect effects (AIE). The aerosol-cloud scheme used is a hybrid bin/bulk model, which treats all phases of clouds and precipitation allowing a detailed analysis of process-level aerosol indirect effects on targeted cloud types. From the simulations, a substantially huge total AIE on maritime clouds of −17.44 ± 6.1 Wm−2 was predicted primarily because maritime clouds are highly sensitive to perturbations in aerosol concentrations because of their low background aerosol concentrations. This was evidenced by the conspicuous increases in droplet and ice number concentrations and the subsequent reductions in particle mean sizes in the present-day. Both the water-only (−9.08 ± 3.18 Wm−2) and the partially glaciated clouds (−8.36 ± 2.93 Wm−2) contributed equally to the net AIE of these maritime clouds. As for the partially glaciated clouds, the mixed-phase component (−14.12 ± 4.94 Wm−2) of partially glaciated clouds was dominant, whilst the ice-only component (5.76 ± 1.84 Wm−2) actually exhibited a positive radiative forcing at the top of the atmosphere (TOA). This was primarily because ice water contents aloft were diminished significantly owing to increased snow production in the present-day.