Assessing the Impacts of Aerosol on the Growth of Cumulus Congestus Clouds

Tropical convection has been observed to contain three modes of convection, the middle mode of which is cumulus congestus clouds. This study investigates the impacts of aerosol, specifically those aerosols that can serve as cloud condensation nuclei, on the growth and development of congestus clouds observed within idealized cloud-resolving model (CRM) simulations conducted under a state of radiative-convective equilibrium. The Regional Atmospheric Modeling System (RAMS) is used here with simulations completed using a large two-dimensional domain (7200 km) at fine resolution (1 km) and long duration (100 days).

Results indicate that congestus in more polluted conditions extend to greater heights more frequently than those developing in clean cases. Greater cloud water mass and ice mass forms in more polluted conditions, though ice forms at a fraction of the rate of the cloud mass. The importance of the warm phase processes, especially vapor diffusional growth of cloud droplets, in the more polluted conditions is highlighted as one such process contributing to congestus vertical development through latent heat release.